Trichloroisocyanuric Acid/Triphenylphosphine-MediatedSynthesis of Benzimidazoles, Benzoxazoles,and Benzothiazoles

Soodabeh Rezazadeh,A Batool Akhlaghinia,A,B and Nasrin RazaviA

ADepartment of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad,

Mashhad 9177948974, Iran.BCorresponding author. Email: akhlaghinia@um.ac.ir

A new and efficient method for preparation of benzimidazoles, benzoxazoles, and benzothiazoles from reactions ofdifferent carboxylic acids with o-phenylenediamine, o-aminophenol, and o-aminothiophenol in the presence of

triphenylphosphine/trichloroisocyanuric acid system is presented. The desired products have been characterised on thebasis of spectral (infrared, NMR, mass spectrometry) data, and the mechanism of their formation is proposed. Theremarkable advantages are the inexpensive and readily available reagent, simple procedure, mild conditions, and good-to-

excellent yields.

Manuscript received: 26 January 2014.Manuscript accepted: 24 April 2014.

Published online: 25 June 2014.

Introduction

Benzimidazoles, benzoxazoles, and benzothiazoles, as impor-tant N-heterocyclic compounds, have always remained a major

source for therapeutic drugs and have received significantattention.[1] They are considered as privileged structures inthe medicinal chemistry field[2] and are found in a large variety

of natural products.[3] They have been used as antiviral,[4]

antimicrobial,[5] anti-tumour,[6] antibiotic,[7] antifungal,[8]

anticonvulsant,[9] anti-inflammatory,[10] anti-ulcer,[11a] anti-helminthic,[11a] antihypertensive,[11b] and anti-analgesic,[11c]

agents. Moreover, their application in the field of advancedmaterials is worthy of note.[12] A thorough retrospect over thereported routes for the synthesis of benzimidazoles, benzox-

azoles, and benzothiazoles reveals plenty of synthetic methodsthat involve two common approaches. These involve reactionbetween either an appropriate aromatic amine and an aldehyde,

followed by oxidative cyclisation of the imine intermediate, orbetween o-phenylenediamine/o-aminophenol/o-aminothiophenol,as the starting substrates, and a carboxylic derivative understrong acidic conditions.[1b,1d,13–17] However, the above men-

tioned methods suffer from several disadvantages such as harshreaction conditions including the use of corrosive acids, toxiccatalysts, high catalyst costs (often not recoverable and reus-

able), occurrence of side reactions, additional oxidation step(which leads to poor yield and difficulty in the work-up proce-dure), low functional group tolerance, and the need to use

reagents in large excess and long reaction times.Therefore, because of the wide range of pharmacological

properties, commercial and synthetic applications of these hetero

cycles, in addition to overcoming all of the above mentionedproblems, investigating an efficient and straightforward proce-dure for the synthesis of 1, 3-benzazoles is highly sought after.

Results and Discussion

In continuation of our interest to explore the use of trichloro-isocyanuric acid/triphenylphosphine systems,[18] we decided to

study the synthesis of benzimidazoles, benzoxazoles, andbenzothiazoles from the reaction between o-phenylenediamine,o-aminophenol, and o-aminothiophenol and a variety of

substituted carboxylic acids using the trichloroisocyanuric acid/triphenylphosphine system (Scheme 1).

In order to establish the optimum conditions for thepreparation of benzimidazoles, various molar ratios of tri-

chloroisocyanuric acid:PPh3 (triphenylphosphine):PhCOOH:o-phenylenediamine were examined for the synthesis of2-phenyl-1H-benzimidazole in using different solvents and

temperatures as a model reaction (Table 1). As observed, basedon the data, CH3NO2, THF, toluene, and DMF are not appropri-ate solvents for this transformation (Table 1, entries 1–5). We

observed that very low yields of the desired product wereobtained under reflux in CH2Cl2, acetone, CHCl3, and 1,2-dichloroethane (Table 1, entries 6–9). Applying 0.3 : 1 :1 : 1and 0.3 : 1 : 1 : 1.5 molar ratios of trichloroisocyanuric acid:

PPh3 : PhCOOH : o-phenylenediamine under reflux in CH3CNproduced 2-phenyl-1H-benzimidazole in 80% isolated yieldafter 4 h (Table 1, entries 10 and 11). Using anisole as solvent

at 1308C resulted in the desired product in 80% yield after 3 h(Table 1, entry 12). The best yield of 2-phenyl-1H-benzimidazolewas obtained under reflux in 1,4-dioxane. Interestingly, increas-

ing the molar ratio of o-phenylenediamine under reflux in 1,4-dioxane has no influences on the reaction rate (Table 1, entries13 and 14). The effect of reaction temperature on the yield of the

product is another important factor that was studied. Thereaction yield decreased to 10% when the temperature wasdecreased to room temperature (Table 1, entry 15).

CSIRO PUBLISHING

Aust. J. Chem. 2015, 68, 145–155

http://dx.doi.org/10.1071/CH14037

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Full Paper

After establishing the methodology for benzimidazoles, wenext focussed our attention on the synthesis of another importantN-heterocycle benzoxazoles. We examined the reaction between

benzoic acid and o-aminophenol as the model reaction in thepresence of the trichloroisocyanuric acid/triphenylphosphine(TCCA/TPP) system using the same reaction conditions as

above (Table 2). Based on the proposedmechanism in Scheme 2and the results obtained from Table 2, formation of VII byintramolecular cyclisation of V and subsequent dehydration ofVIwas considered as a difficult step towards the construction of

N-heterocyclic compounds. In the presence of CH3NO2 andDMF, IIwas formed in low concentrations, and did not have anytendency to react with o-aminophenol (Table 2, entries 1 and 2).

No product formationwas observedwhen the reactionwas carriedout in 1,2-dichloroethane, acetone, CH3CN, CHCl3, CH2Cl2,THF, toluene, and anisole using a 0.3 : 1 : 1 : 1.5 molar ratio

of trichloroisocyanuric acid : PPh3 : PhCOOH : o-aminophenol(Table 2, entries 3–10). After long periods of time, only V wasformed in the above-mentioned solvents with different isolated

yields. As observed from Tables 1 and 2, 1,4-dioxane seemed tobe a better solvent in termsof obtaining the desiredN-heterocycliccompound. Under reflux in 1,4-dioxane, only the amide inter-mediate V was obtained with 95% isolated yield. However, at

this temperature formation of VII from cyclisation and dehy-dration of V were not observed (Table 2, entry 11). Hence, theresults obtained fromTable 2 lead us to conclude that cyclisation

and dehydration steps are strongly dependent on temperature.

To achieve good yields of the desired product, the reaction wasperformed in 1,4-dioxane at various temperatures. According tothe results obtained from Table 2, increasing the reaction

temperature benefited the yield of 2-phenyl-benzoxazole. Forexample, when the reaction was performed at 1308C and 1608C(the reaction was performed in a sealed tube), the desired

product was obtained after an extended reaction period in30% and 85% isolated yields, respectively (Table 2, entries12 and 13). The rate of reaction was efficiently increased whenthe reaction was carried out at 1908C, producing 97% isolated

yield of 2-phenyl-benzoxazole (Table 2, entry 14). It seems thatthe choice of temperature was crucial for cyclisation of theamide intermediateV. To investigate the effect of molar ratio of

o-aminophenol, the reaction was carried out in 1,4-dioxane inthe presence of 0.3 : 1 : 1 : 1 molar ratio of trichloroisocyanuricacid : PPh3 : PhCOOH : o-aminophenol at 1908C. According to

this study, decreasing the molar ratio of o-aminophenol leads to80% yield of the desired product and 10% of the amideintermediate V (Table 2, entry 15).

To widen the applicability of the present protocol, weinvestigated the synthesis of thia-analogues of benzimidazoles:benzothiazoles (whose structures are found in various bioactivemolecules) using the TCCA/TPP system. Under the optimised

reaction conditions established for preparation of benzimida-zoles and benzoxazoles, 2-phenylbenzothiazole was synthesisedfrom the reaction between benzoic acid and o-aminothiophenol

under reflux in 1,4-dioxane, using a 0.3 : 1 : 1 : 1 molar ratio of

PPh3,

N

O

N

ON

O

Cl

Cl

ClRO

HO�

NH2

XH1, 4-dioxane, reflux or 190�C

N

XR

X � NH, O, SR � aryl, alkyl, heteroaryl

Scheme 1. Synthesis of benzimidazoles, benzoxazoles, and benzothiazoles.

Table 1. Conversion of benzoic acid into 2-phenyl-1H-benzimidazole using the TCCA/TPP/benzoic acid/o-phenylenediamine

system under different reaction conditions

Entry Trichloroisocyanuric acid : PPh3 :

PhCOOH : o-phenylenediamine

Solvent Temperature [8C] Time [h] Isolated yield [%]

1 0.3 : 1 : 1 : 1 CH3NO2 reflux 24 0

2 0.3 : 1 : 1 : 1.5 CH3NO2 reflux 24 0

3 0.3 : 1 : 1 : 1.5 THF reflux 24 0

4 0.3 : 1 : 1 : 1.5 Toluene reflux 18 0

5 0.3 : 1 : 1 : 1.5 DMF 150 22 0

6 0.3 : 1 : 1 : 1.5 CH2Cl2 reflux 18 10

7 0.3 : 1 : 1 : 1.5 Acetone reflux 24 10

8 0.3 : 1 : 1 : 1.5 CHCl3 reflux 24 30

9 0.3 : 1 : 1 : 1.5 1,2-C2H4Cl2 reflux 24 40

10 0.3 : 1 : 1 : 1 CH3CN reflux 4 80

11 0.3 : 1 : 1 : 1.5 CH3CN reflux 4 80

12 0.3 : 1 : 1 : 1.5 PhOMe 130 3 80

13 0.3 : 1 : 1 : 1.5 1,4-Dioxane reflux 1 90

14 0.3 : 1 : 1 : 1 1,4-Dioxane reflux 1 90

15 0.3 : 1 : 1 : 1 1,4-Dioxane rtA 24 10

ART: room temperature

146 S. Rezazadeh, B. Akhlaghinia, and N. Razavi

trichloroisocyanuric acid : PPh3 : PhCOOH : o-aminothiophenol,in high yields (Table 3).

Under the optimised reaction conditions established, asobserved in Table 4, heterocyclisations of differently substituted

aromatic carboxylic acids, hetero-aromatic, and aliphaticcarboxylic acids with o-phenylenediamine, o-aminophenol,and o-aminothiophenol were carried out. In general, most of

the reactions proceeded smoothly to give corresponding

products in good-to-excellent yields. o-Aminophenol showeda lower reactivity than that of o-phenylenediamine ando-aminothiophenol towards carboxylic acids. Most probably,because of the low nucleophilicity of the attached hydroxyl

group to the phenyl ring in o-aminophenol, the nucleophilicattack of OH on amide intermediate V (Scheme 2) was per-formed at a higher reaction temperature and also a longer

reaction time was used when compared with the reactions

Table 2. Conversion of benzoic acid into 2-phenylbenzoxazole using the TCCA/TPP/benzoic acid/o-aminophenol

system under different reaction conditions

Entry Trichloroisocyanuric acid : PPh3 :

PhCOOH : o-aminophenol

Solvent Temperature [8C] Time [h] Isolated yield

of V/VII [%]A

1 0.3 : 1 : 1 : 1.5 CH3NO2 reflux 24 0/0

2 0.3 : 1 : 1 : 1.5 DMF 150 24 0/0

3 0.3 : 1 : 1 : 1.5 1,2-C2H4Cl2 reflux 15 20/0

4 0.3 : 1 : 1 : 1.5 Acetone reflux 20 60/0

5 0.3 : 1 : 1 : 1.5 CH3CN reflux 21 80/0

6 0.3 : 1 : 1 : 1.5 CHCl3 reflux 22 90/0

7 0.3 : 1 : 1 : 1.5 CH2Cl2 reflux 22 90/0

8 0.3 : 1 : 1 : 1.5 THF reflux 15 90/0

9 0.3 : 1 : 1 : 1.5 Toluene reflux 15 95/0

10 0.3 : 1 : 1 : 1.5 PhOMe 130 22 95/0

11 0.3 : 1 : 1 : 1.5 1,4-Dioxane reflux 15 95/0

12B 0.3 : 1 : 1 : 1.5 1,4-Dioxane 130 21 60/30

13B 0.3 : 1 : 1 : 1.5 1,4-Dioxane 160 8 10/85

14B 0.3 : 1 : 1 : 1.5 1,4-Dioxane 190 4 0/97

15B 0.3 : 1 : 1 : 1 1,4-Dioxane 190 6 10/80

AV and VII correspond to amide intermediate V and final product in Scheme 2.BReactions were performed in a sealed tube.

NN

N

O

O

O Cl

Cl

Cl3 PPh33 RCOOH

HNNH

NH

O

O

O

O

R OPPh3

HX

H2N

Cl3 O � PPh3 � 3 HCl�

HN

O

R

HX

X

HN OH

R

�H2O

X

NR

X � NH, O, S

3

� NN

N

O

O

O

PPh3Cl

PPh3Cl

NN

N

HO

OH

HO

III

IV

�

I

II V

VI

PPh3Cl�

�

�

�

�

�

�

�

VII

Scheme 2. Synthesis mechanism of 1,3-benzazoles.

Synthesis of 1,3-Benzazoles 147

Table 3. Conversion of benzoic acid into 2-phenylbenzothiazole using the TCCA/TPP/benzoic acid/o-aminothiophenol

system under different reaction conditions

Entry Trichloroisocyanuric acid : PPh3 :

PhCOOH : o-aminothiophenol

Solvent Temperature [8C] Time [min] Isolated yield [%]

1 0.3 : 1 : 1 : 1 1,4-Dioxane rtA 2 h 80

2 0.3 : 1 : 1 : 1 1,4-Dioxane 60 1 h 80

3 0.3 : 1 : 1 : 1 1,4-Dioxane reflux 5 90

4B 0.3 : 1 : 1 : 1 1,4-Dioxane 150 5 90

ART: room temperature.BThe reaction was performed in a sealed tube.

Table 4. Synthesis of different structurally benzimidazoles, benzoxazoles, and benzothiazoles using the TCCA/TPP system

Entry Substrate Product Time [h]/Isolated yield [%]

1 Benzoic acidN

X 1/90 X¼NH (1a)

4/97 X¼O (1b)

5(min)/90 X¼S (1c)

2 4-Nitrobenzoic acidN

XNO2

2/70 X¼NHA (2a)

2/90 X¼O (2b)

2/85 X¼SA (2c)

3 3-Nitrobenzoic acid

N

XNO2

2/90 X¼NHA (3a)

4/95 X¼O (3b)

3/80 X¼SA (3c)

4 3,5-Dichlorobenzoic acid

N

XCl

Cl

40(min)/95 X¼NH (4a)

5/95 X¼O (4b)

15(min)/95 X¼S (4c)

5 4-Chlorobenzoic acidN

XCl

1/97 X¼NH (5a)

5/95 X¼O (5b)

5(min)/95 X¼S (5c)

6 2-Chlorobenzoic acid

N

XCl

2/80

7/70

5(min)/80

X¼NH (6a)

X¼O (6b)

X¼S (6c)

7 4-Bromobenzoic acidN

XBr

1.5/95 X¼NH (7a)

5/90 X¼O (7b)

15(min)/95 X¼S (7c)

8 4-Methylbenzoic acidN

X 2/85 X¼NH (8a)

5/95 X¼O (8b)

3/80 X¼S (8c)

9 3,5-Dimethylbenzoic acidN

X 2.5/80

6/90

3/95

X¼NH (9a)

X¼O (9b)

X¼S (9c)

10 4-Methoxybenzoic acidN

XOMe

3/90 X¼NH (10a)

6/95 X¼O (10b)

2/80 X¼S (10c)

11 (E)-Cinnamic acid N

X 3/80 X¼NH (11a)

6/95 X¼O (11b)

3/70 X¼S (11c)

(Continued )

148 S. Rezazadeh, B. Akhlaghinia, and N. Razavi

involving the two other nucleophiles (NH and SH groups) ino-phenylenediamine and o-aminothiophenol. Based on the

results from Table 4 and the proposed mechanism in Scheme 2,amide intermediates V and VI can be referred as two keyintermediates of the heterocyclisation reaction. In all reactions,

amide intermediate V was formed by nucleophilic attack ofNH of the corresponding amine on II, regardless of the typeof carboxylic acids. Cinnamic acid and aliphatic carboxylic

acids, as well as benzoic acid and substituted benzoic acidsreacted smoothly with o-phenylenediamine, o-aminophenol,and o-aminothiophenol, and produced the corresponding hetero-cycle compounds (Table 4, compare entries 1–10 with entries

11–17). Heteroaromatic carboxylic acids were converted readilyinto the corresponding heterocycle compounds when comparedwith the other mentioned carboxylic acids (Table 4, entries

18 and 19).

To further expand the scope of the reaction, substitutedo-phenylenediamine and o-aminophenol were employed as

substrates to react with benzoic acid in the presence of theTCCA/TPP system. The reaction was significantly affected bythe substituents on the aromatic ring of o-phenylenediamine

and o-aminophenol. When 4-chlorobenzene-1,2-diamine wasreacted with benzoic acid, amide intermediate V and corre-sponding benzimidazole were obtained after 1 h with a yield of

50/50%. Considerable progress was not achieved at 1908C in1,4-dioxane after 21 h. Under optimised conditions, no desiredbenzoxazole was detected from the reaction between 2-amino-5-chlorophenol and benzoic acid. The amide intermediateVwas

formed in 30% yield, which remained unchanged followingreaction at 1908C in 1,4-dioxane for 20 h. It must be pointed outthat the presence of an electron-deficient substituent slowed the

reactions and decreased the yields.

Table 4. (Continued)

Entry Substrate Product Time [h]/Isolated yield [%]

12 4-Chlorocinnamic acid N

X

Cl

1/95 X¼NH (12a)

6/90 X¼O (12b)

2/75 X¼S (12c)

13 Phenylacetic acid N

X1/70

6/85

3/90

X¼NHA (13a)

X¼O (13b)

X¼S (13c)

14 4-Methoxyphenylacetic acidN

X

OMe

6/85 X¼O (14b)

15 Diphenyl acetic acidN

X 2/85

7/65

2/80

X¼NHA (15a)

X¼O (15b)

X¼S (15c)

16 Oleic acidN

XCH2(CH2)6CH � CH(CH2)7CH3 6/85 X¼O (16b)

17 Stearic acidN

XCH2(CH2)15CH3

2.5/98 X¼NH (17a)

6/90 X¼O (17b)

1/90 X¼S (17c)

18 3-Thiophene carboxylic acidN

X S1/80 X¼NH (18a)

5/70 X¼O (18b)

1/90 X¼S (18c)

19 4-Pyridine carboxylic acidN

XN

0.5/80 X¼NH (19a)

2/90 X¼O (19b)

20 Benzoic acidN

O

1/95 X¼O (20b)

AMolar ratio of RCOOH/o-phenylenediamine (1 : 1.5).

Synthesis of 1,3-Benzazoles 149

The presence of an electron-donating substituent (CH3) on

the para-position of the phenyl ring accelerates the formation ofamide intermediate V that leads to formation of the desiredproduct in shorter reaction times (Table 4, entry 20).

In our experiments, completion of the reaction was con-firmed by the disappearance of the carboxylic acids and thenamide intermediateV on TLC, followed by the disappearance ofacidic OH stretching frequency at 3400–2400 cm�1 in the

Fourier transform infrared (FTIR) spectra. The resultingN-heterocycle compounds, after purification via either crystal-lisation or column chromatography were characterised using

FTIR, NMR, and mass spectrometry (MS). Absorption bands at3395–2400, 1679–1590, and 1388–1306 cm�1, correspondingto NH, C¼N, and C–N groups of benzimidazoles, respectively

confirmed the formation of benzimidazoles. Formation ofbenzoxazoles were also confirmed by the appearance of absorp-tion bands at 1639–1597 and 1250–1225 cm�1 that correspondto C¼N and C–O groups of benzoxazoles, respectively.

Absorption band at 1748–1511 cm�1 confirmed the presenceof C¼N group of benzothiazoles. In the 1H NMR spectrum, theNH proton of benzimidazoles showed a downfield shift at

12.70–12.38 ppm. In the 13C NMR spectrum, signals around150.9–148.6, 165–159, and 168.60–164.90 ppm that wereassigned to the quaternary carbon atom of benzimidazole,

benzoxazole, and benzothiazole, respectively, were observed.All of the products obtained were known compounds andcharacterised by comparison of their melting points with those

of reported compounds.According to the above observations and previous report in

the literature,[18] a pathway for the overall process wasproposed, as shown in Scheme 2. The initial attack at the

halogen in TCCA by triphenylphosphine leads to the halogen–phosphonium salt I. The reaction between the halogen–phosphonium salt and carboxylic acid yields the activated

carboxylic acid species II and [1,3,5]triazine-2,4,6-triol (III),which is in equilibrium with [1,3,5]triazinane-2,4,6-trione(IV). As soon as II is formed, a nucleophilic attack occurs

between II and the corresponding amine to form triphenylpho-sphine oxide and amide intermediate V (at room temperature).Upon heating the reaction mixture (101–1908C), amide inter-mediate V may be gradually transformed into VI by intra-

molecular cyclisation. Subsequently thermal dehydration of VIgives the corresponding N-heterocyclic compound VII. Toelucidate the reaction path more clearly, we attempted to

isolate and identify III, IV, and V.FTIR spectra of the two tautomeric forms [1,3,5]triazine-

2,4,6-triol (III) and [1,3,5]triazinane-2,4,6-trione (IV) showed a

broad absorption band at 3350–3100 cm�1, owing to OH andNH stretching vibration of III and IV. The presence of C¼NandC¼O was confirmed by the appearance of absorption bands at

1613 and 1755–1713 cm�1, respectively.Amide intermediate V was also isolated, purified, and

identified by melting point analysis and FTIR spectroscopy.Absorption bands at 3272/3056–2594/3360 (X¼NH/O/S) and

1644/1644/1598 (X¼NH/O/S) cm�1, corresponding to NH andC¼O groups, confirmed the formation of the amide linkages ofamide intermediate V. In addition, two absorption bands,

corresponding to the stretching vibration of NH2 (X¼NH),were observed at 3444 and 3370 cm�1. A broad absorption at3411 (X¼O) and a weak absorption band at 2586 (X¼S) cm�1

confirmed the respective presence of OH and SH groups of thecorresponding amide intermediate V. Further investigation ofthe reaction mechanism is ongoing in our group.

Conclusion

We have developed a simple, practical, highly efficient, andconvenient method for the synthesis of benzimidazoles,benzoxazoles, and benzothiazoles via the condensation of

o-phenylenediamine, o-aminophenol, and o-aminothiophenolwith various carboxylic acids. By using carboxylic acids as thestarting materials, we have eliminated the need for toxic oxi-

dants that are necessary for the reaction to proceed when eitheralcohols or aldehydes are used. Moreover, the present protocolaffords several significant advantages (i) good-to-excellent

product yields, (ii) high level of generality and applicability toa broad range of substrates, (iii) mild reaction conditionsrequirements in the absence of harsh activating reagents, (iv)

the use of inexpensive and readily available reagents andpromoters, thereby increasing the level of usefulness ofthe reaction, and (v) easy purification procedure. Owing to theadvantages of the current method, the latter presents a valid

contribution to the existing methodologies.

Experimental

General

The products were purified by column chromatography.Determination of the product purity was accomplished by TLCon silica gel poly gram STL G/UV 254 plates. The melting

points of products were determinedwith an Electrothermal Type9100 melting point apparatus. The FTIR spectra were recordedon an Avatar 370 FT-IR Thermal Nicolet spectrometer. The

NMR spectra were recorded on a Brucker Avance 400MHzinstrument in [D6]DMSO and CDCl3. All of the products wereknown compounds and characterised by the IR, and 1HNMRand13CNMR spectroscopies, and comparison of their melting pointswith those of known compounds. Elemental analyses wereperformed using a Thermo Finnegan Flash EA 1112 Series

instrument.Mass spectra were recordedwith a CH7AV ariamatBremem instrument at 70 eV.

Typical Procedure for the Preparation of2-Phenyl-1H-benzimidazole

To a cold solution of triphenylphosphine (0.262 g, 1mmol)in 1,4-dioxane (6mL), trichloroisocyanuric acid (0.076 g,0.3mmol) was added with continuous stirring. Benzoic acid

(0.122 g, 1mmol) was added, and stirring was continued for30min. The temperature was raised to room temperature.o-Phenylenediamine (0.108 g, 1mmol) was added, and stirring

of the pale yellow suspension was continued for 1 h underrefluxing conditions. The progress of the reaction wasmonitoredby TLC. Upon completion of the reaction, the crude product was

filtered, washed with CHCl3 (10mL), and re-crystallised fromethanol. 2-Phenyl-1H-benzimidazole was obtained in 90% yield(0.174 g).

Typical Procedure for the Preparation of 2-Phenyl-benzoxazole

To a cold solution of triphenylphosphine (0.262 g, 1mmol) in1,4-dioxane (6mL), trichloroisocyanuric acid (0.076 g,

0.3mmol) was added with continuous stirring. Benzoic acid(0.122 g, 1mmol) was added, and stirring was continued for30min. The temperature was raised to room temperature.

o-Aminophenol (0.164 g, 1.5mmol) was added, and stirring wascontinued in a sealed tube for 4 h at 1908C. The progress of thereaction was monitored by TLC. Upon completion of the

150 S. Rezazadeh, B. Akhlaghinia, and N. Razavi

reaction, the reaction mixture was cooled and the resulting

mixture was purified by thin layer chromatography using ethylacetate/n-hexane (1 : 1, v/v) as eluent; 2-phenyl-benzoxazolewas obtained in 97% yield (0.188 g).

Typical Procedure for the Preparationof 2-Phenyl-benzothiazole

To a cold solution of triphenylphosphine (0.262 g, 1mmol) in1,4-dioxane (6mL), trichloroisocyanuric acid (0.076 g,0.3mmol) was added with continuous stirring. Benzoic acid

(0.122 g, 1mmol) was added, and stirring was continued for30min. The temperature was raised to room temperature.o-Aminothiophenol (0.125 g, 1mmol) was added and stirring

was continued for 5min at reflux. The progress of the reactionwas monitored by TLC. Upon completion of the reaction, thereaction mixture was cooled and the resulting mixture waspurified by thin layer chromatography using ethyl acetate/

n-hexane (1 : 3, v/v) as eluent; 2-phenyl-benzothiazole wasobtained in 90% yield (0.190 g).

2-Phenyl-1H-benzo[d]imidazole (1a): mp 287–2888C (lit.

287–2888C[19]). nmax (KBr)/cm�1 3150–2530 (NH), 1625(C¼N), 1510, 1460, 1379 (C–N), 1231, 872, 752, 698, 622,527. dH ([D6]DMSO, 400MHz) 8.21–8.18 (2H, m, Ar), 7.75–

7.71 (2H, m, Ph), 7.68–7.62 (3H, m, Ph), 7.41–7.37 (2H, m, Ar).m/z (EI (electron impact)) 194 (62.5%, [M]þ).

2-Phenyl benzo[d]oxazole (1b): mp 102–1038C (lit. 102–

1038C[14b]). nmax (KBr)/cm�1 3060, 1617 (C¼N), 1552, 1472,

1446, 1343, 1241 (C–O), 1200, 1052, 1022, 924, 804, 745, 687.dH (CDCl3, 400MHz) 8.28 (2H, dd, J 6.4, 4, Ph), 7.82–7.79 (1H,m,Ar), 7.60–7.57 (1H,m,Ar), 7.54–7.50 (3H,m, Ph), 7.39–7.34

(2H, m, Ar). dC (CDCl3, 100MHz) 163.0 (–C¼N), 150.7(¼C–O), 142.1 (¼C–N), 131.5, 128.9, 127.6, 127.1, 125.1,124.5, 120.0, 110.6. m/z (EI) 195 (87%, [M]þ).

2-Phenyl benzo[d]thiazole (1c): mp 113–1148C (lit. 112–1148C[20]). nmax (KBr)/cm�1 3060, 3019, 2929, 2847, 1511(C¼N), 1477, 1432, 1313, 1224, 1160, 1074, 963, 764, 730,

688, 624. dH (CDCl3, 400MHz) 8.13–8.11 (1H, m, Ph), 8.11–8.09 (2H, m, Ar), 7.93 (1H, d, J 8.0, Ar), 7.54–7.50 (4H, m, Ph),7.41 (1H, td, J 8.4, 1.2, Ar). m/z (EI) 211 (63%, [M]þ). Anal.Calc. for C13H9NS: C 73.90, H 4.29, N 6.63, S 15.18. Found:

C 73.62, H 4.06, N 6.36, S 15.06%.2-(4-Nitrophenyl)-1H-benzo[d]imidazole (2a): mp 302–

3058C (lit. 304–3068C[21]). nmax (KBr)/cm�1 3141–2400 (NH),

1629 (C¼N), 1605, 1525, 1450, 1401, 1381 (C–N), 1351, 1229,1111, 1000, 868, 853, 754, 702, 617, 544, 493. dH ([D6]DMSO,400MHz) 8.67 (2H, d, J 8.8, Ph), 8.37 (2H, d, J 8.8, Ph), 7.85

(2H, dd, J 6.4, 3.2, Ar), 7.54 (2H, dd, J 6.0, 3.2, Ar).m/z (EI) 239(78%, [M]þ).

2-(4-Nitrophenyl) benzo[d]oxazole (2b): mp 269–2728C (lit.

271–2738C[22]). nmax (KBr)/cm�1 3113, 3092, 1597 (C¼N),1554, 1521, 1450, 1347, 1225 (C–O), 1106, 1056, 855, 752,706, 493. dH (CDCl3, 400MHz) 8.46 (2H, dt, J 9.2, 2.0, Ph), 8.41(2H, dt, J 9.2, 2.0, Ph), 7.86–7.84 (1H,m, Ar), 7.67–7.65 (1H,m,

Ar), 7.49–7.42 (2H, m, Ar).2-(4-Nitrophenyl) benzo[d]thiazole (2c): mp 229–2308C (lit.

228–2308C[23]). nmax (KBr)/cm�1 3060, 1599 (C¼N), 1521,

1425, 1343, 1313, 1108, 970, 855, 766, 728, 686. dH (CDCl3,400MHz) 8.36 (2H, dt, J 8.8, 2.0, Ph), 8.27 (2H, dt, J 8.8, 2.0, Ph),8.15 (1H, d, J 7.8, Ar), 7.97 (1H, d, J 7.8, Ar), 7.57 (1H, td, J 7.2,

1.2, Ar), 7.48 (1H, td, J 7.2, 1.2, Ar). m/z (EI) 256 (11%, [M]þ).2-(3-Nitrophenyl)-1H-benzo[d]imidazole (3a): mp185–

1878C (lit. 185–1878C[24]). nmax (KBr)/cm�1 3313–2500 (NH),

1634 (C¼N), 1530, 1486, 1348 (C–N), 1233, 1123, 918, 811,

739, 703, 620, 540. dH ([D6]DMSO, 400MHz) 9.03 (1H, s, Ph),8.64 (1H, d, J 7.6, Ph), 8.32 (1H, d, J 8.0, Ph), 7.84 (1H, t, J 8.0,Ph), 7.65 (2H, dd, J 6.0, 3.2, Ar), 7.24 (2H, dd, J 4.4, 3.2, Ar). dC([D6]DMSO, 100MHz) 149.6 (–C¼N), 148.8 (¼C–NO2),139.1 (¼C–N), 132.9, 132.3, 131.1, 124.6, 123.0, 121.3, 115.9.

2-(3-Nitrophenyl) benzo[d]oxazole (3b): mp 205–2078C (lit.2078C[25]). nmax (KBr)/cm�1 3096, 2921, 2859, 1609 (C¼N),

1528, 1472, 1451, 1351, 1245 (C–O), 1098, 1053, 807, 765, 743,705, 665. dH (CDCl3, 400MHz) 9.12 (1H, t, J 1.6, Ph), 8.61 (1H,dt, J 7.6, 1.2, Ph), 8.40 (1H, dt, J 7.2, 1.2, Ph), 7.85–7.83 (1H, m,

Ar), 7.76 (1H, t, J 8.0, Ph), 7.67–7.65 (1H, m, Ar), 7.47–7.41(2H, m, Ar). m/z (EI) 240 (12%, [M]þ).

2-(3-Nitrophenyl) benzo[d]thiazole (3c): mp185–1868C (lit.

185–1868C[23]). nmax (KBr)/cm�1 3092, 1580 (C¼N), 1529,1433, 1346, 1315, 1225, 1102, 984, 886, 761, 739, 671. dH(CDCl3, 400MHz) 8.96 (1H, t, J 2.0, Ph), 8.44 (1H, dt, J 7.6, 1.4,Ph), 8.37–8.34 (1H, m, Ph), 8.14 (1H, d, J 8.0, Ar), 7.97 (1H, dd,

J 4.6, 0.4, Ar), 7.71 (1H, t, J 8.0, Ph), 7.57 (1H, td, J 8.0, 1.2, Ar),7.48 (1H, td, J 8.0, 1.2, Ar). dC (CDCl3, 100MHz) 164.9(–C¼N), 153.9 (¼C–N), 148.7 (C–NO2), 135.3 (¼C–S),

135.1, 133.0, 130.1, 126.8, 126.0, 125.2, 123.7, 122.3, 121.8.2-(3,4-Dichlorophenyl)-1H-benzo[d]imidazole (4a): mp

225–2278C (lit. 2298C[26]). nmax (KBr)/cm�1 3395–2520 (NH),

1629 (C¼N), 1515, 1464, 1447, 1428, 1229, 1325 (C–N), 1141,1030, 894, 820, 738, 677, 506 cm�1. dH ([D6]DMSO, 400MHz)8.47 (1H, s, Ph), 8.19 (1H, d, J 8.4, Ph), 7.90 (1H, d, J 8.4, Ph),

7.69 (2H, s, Ar), 7.35 (2H, s, Ar). dC ([D6]DMSO, 100MHz)148.6 (–C¼N), 140.0 (¼C–N), 137.3, 133.9, 132.4, 131.9,129.0, 127.4, 124.2, 115.5, 115.4. m/z (EI) 263 (98%, [M]þ),265 (28%, [Mþ2]þ).

2-(3,4-Dichlorophenyl) benzo[d]oxazole (4b): mp 143–1458C (lit. 144–1458C[1d]). nmax (KBr)/cm

�1 3084, 3051, 1621(C¼N), 1546, 1465, 1453, 1394, 1377, 1241 (C–O), 1134, 1064,

1029, 886, 820, 741, 676, 440. dH (CDCl3, 400MHz) 8.38 (1H,d, J 2.0, Ph), 8.10 (1H, dd, J 8.4, 2.0, Ph), 7.81–7.79 (1H, m, Ar),7.64 (1H, s, Ph), 7.62–7.60 (1H, m, Ar), 7.42–7.38 (2H, m, Ar).

m/z (EI) 264 (34%, [M]þ), 266 (3%, [Mþ2]þ).2-(3,4-Dichlorophenyl) benzo[d] thiazole (4c): mp 122–

1238C (lit. 123–1248C[20]). nmax (KBr)/cm�1 3101, 1555(C¼N), 1504, 1463, 1432, 1374, 1310, 1229, 1136, 1028, 984,

865, 824, 757, 725, 692, 669, 432. dH (CDCl3, 400MHz) 8.23(1H, d, J 2.0, Ar), 8.10 (1H, d, J 8.2, Ar), 7.94 (1H, d, J 0.4, Ph),7.91 (1H, dd, J 8.4, 2.4, Ph), 7.58 (1H, d, J 8.4, Ph), 7.54 (1H, td,

J 7.8, 1.2, Ar), 7.44 (1H, td, J 8.0, 1.2, Ar).2-(4-Chlorophenyl)-1H-benzo[d]imidazole (5a): mp 281–

2848C (lit. 282–2858C[27]). nmax (KBr)/cm�1 3313–2529 (NH),

1627 (C¼N), 1602, 1489, 1458, 1379 (C–N), 1232, 1092, 1012,837, 749, 616, 528, 501. dH ([D6]DMSO, 400MHz) 8.38 (2H,dd, J 4.8, 2.0, Ar), 7.84–7.81 (4H,m, Ph) 7.53 (2H, dd, J 6.2, 2.8,

Ar). m/z (EI) 228 (90%, [M]þ), 229 (11%, [Mþ 1]þ).2-(4-Chlorophenyl) benzo[d]oxazole (5b): mp 150–1528C

(lit. 150–1528C[28]). nmax (KBr)/cm�1 3092, 3060, 1617 (C¼N),

1484, 1452, 1405, 1343, 1244 (C–O), 1091, 1056, 1011, 927,

832, 758, 739, 497. dH (CDCl3, 400MHz) 8.21 (2H, dt, J 8.8,2.4, Ar), 7.80–7.77 (1H, m, Ph), 7.61–7.58 (1H, m, Ph), 7.52(2H, dt, J 8.8, 2.4, Ar), 7.41–7.36 (2H, m, Ph).

2-(4-Chlorophenyl) benzo[d]thiazole (5c): mp 113–1148C(lit. 114–1168C[20]). nmax (KBr)/cm

�1 3056, 2925, 2851, 1585(C¼N), 1474, 1433, 1398, 1315, 1233, 1089, 1008, 969, 828,

756, 730, 691, 482. dH (CDCl3, 400MHz) 8.09 (1H, d, J 8.0, Ar),8.05 (2H, dt, J 8.8, 2.0, Ph), 7.92 (1H, d, J 8.0, Ar), 7.55–7.53(1H, m, Ar), 7.49 (2H, dt, J 8.8, 2.0, Ph), 7.42 (1H, td, J 8.0, 1.2,

Synthesis of 1,3-Benzazoles 151

Ar). m/z (EI) 245 (82.5%, [M]þ), 247 (27.5%, [Mþ2]þ). Anal.Calc. for C13H8ClNS: C 63.54, H 3.28, N 5.70, S 13.05. Found:C 63.26, H 3.18, N 5.61, S 12.95%.

2-(2-Chlorophenyl)-1H-benzo[d]imidazole (6a): mp 226–

2288C (lit. 227–2298C[24]). nmax (KBr)/cm�1 3100–2500 (NH),

1590 (C¼N), 1443, 1404, 1373, 1316 (C–N), 1274, 1054, 973,751, 731. dH ([D6]DMSO, 400MHz) 2.7 (1H, br s, NH), 7.72–7.24 (8H, m, Ph, Ar). m/z (EI) 228 (32%, [M]þ), 229 (6%,

[Mþ 1]þ).2-(2-Chlorophenyl) benzo[d]oxazole (6b): mp 68–708C (lit.

69–708C[29]). nmax (KBr)/cm�1 3068, 1609 (C¼N), 1568, 1535,

1452, 1430, 1343, 1311, 1249 (C–O), 1086, 1021, 918, 813, 761,746, 729, 461. dH (CDCl3, 400MHz) 8.17 (1H, dd, J 7.4, 2.0,Ph), 7.89–7.86 (1H,m, Ph), 7.65–7.62 (1H,m, Ph), 7.59 (1H, dd,

J 8.0, 1.6, Ph), 7.49–7.38 (4H, m, Ar).2-(2-Chlorophenyl) benzo[d]thiazole (6c): mp 80–828C (lit.

80–828C[20]). nmax (KBr)/cm�1 3056, 1556 (C¼N), 1479, 1427,

1315, 1270, 1221, 1059, 1036, 967, 865, 758, 729, 684. dH(CDCl3, 400MHz) 8.23 (1H, dd, J 5.6, 3.6, Ph), 8.16 (1H, d,J 8.4, Ar), 7.98 (1H, d, J 8.0, Ar), 7.57–7.53 (2H, m, Ar), 7.48–7.43 (3H,m, Ph).m/z (EI) 245 (41%, [M]þ) 247 (7%, [Mþ2]þ).

2-(4-Bromophenyl)-1H-benzo[d]imidazole (7a): mp 291–2938C (lit. 292–2938C[30]). nmax (KBr)/cm

�1 3325–2528 (NH),1626 (C¼N), 1599, 1490, 1456, 1378 (C–N), 1231, 1073, 1010,

830, 739, 616. dH ([D6]DMSO, 400MHz) 8.26 (2H, d, J 8.8,Ar), 7.94 (2H, d, J 8.8, Ar), 7.81–7.78 (2H, m, Ph), 7.50 (2H, dd,J 6.0, 3.2, Ph).m/z (EI) 273 (50%, [M]þ), 275 (33%, [Mþ2]þ).

2-(4-Bromophenyl) benzo[d]oxazole (7b): mp 157–1588C(lit. 157–1588C[1b]). nmax (KBr)/cm

�1 3084, 3051, 1614 (C¼N),1591, 1548, 1483, 1451, 1400, 1343, 1244 (C–O), 1180, 1069,1052, 1008, 925, 830, 740, 716, 494. dH (CDCl3, 400MHz) 8.14

(2H, dt, J 8.8, 2.0, Ar), 7.80–7.78 (1H,m, Ph), 7.69 (2H, dt, J 8.8,2.0, Ar), 7.61–7.59 (1H, m, Ph), 7.41–7.37 (2H, m, Ph).m/z (EI)274 (90%, [M]þ), 272 (100%, [M–2]þ).

2-(4-Bromophenyl) benzo[d]thiazole (7c): mp 128–1298C(lit. 127–1298C[31]). nmax (KBr)/cm

�1 3064, 3031, 2913, 2851,1589 (C¼N), 1503, 1475, 1401, 1319, 1221, 1070, 1008, 969,

826, 752, 721, 681, 481. dH (CDCl3, 400MHz) 8.09 (1H, dd,J 8.0, 0.4, Ar), 7.98 (2H, dt, J 8.4, 2.4, Ph), 7.93 (1H, dd, J 8.2,0.4, Ar), 7.65 (2H, dt, J 8.4, 2.4, Ph), 7.53 (1H, td, J 8.0, 1.2, Ar),7.42 (1H, td, J 7.6, 1.2, Ar).

2-p-Tolyl-1H-benzo[d]imidazole (8a): mp 274–276 (lit.274–2768C[32]). nmax (KBr)/cm�1 3056–2500 (NH), 1621(C¼N), 1500, 1447, 1430, 1398, 1369 (C–N), 1274, 1229,

1123, 964, 821, 746, 726, 545, 489. dH ([D6]DMSO,400MHz) 12.81 (1H, br s, NH), 8.07 (2H, d, J 8.0, Ph), 7.58(2H, m, Ar), 7.35 (2H, d, J 8.0, Ph), 7.18 (2H, dd, J 6.3, 2.8, Ar),

2.38 (3H, s, Me). m/z (EI) 208 (100%, [M]þ).2-p-Tolyl benzo[d]oxazole (8b): mp 103–1058C (lit.105–

1068C[33]). nmax (KBr)/cm�1 3060, 3023, 2917, 2851, 1621

(C¼N), 1555, 1501, 1451, 1409, 1348, 1243 (C–O), 1172,1115, 1055, 1016, 820, 746, 726, 501. dH (CDCl3, 400MHz)8.17 (2H, d, J 8.0, Ph), 7.79–7.77 (1H,m, Ph), 7.60–7.58 (1H,m,Ph), 7.38–7.34 (4H, m, Ar), 2.46 (3H, s, Me).

2-p-Tolyl benzo[d]thiazole (8c): mp 83–848C (lit. 80–848C[20]). nmax (KBr)/cm�1 3060, 3023, 2908, 1609 (C¼N),1527, 1484, 1433, 1407, 1312, 1226, 1181, 959, 817, 761, 729,

691, 622, 482. dH (CDCl3, 400MHz) 8.08 (1H, d, J 8.0, Ar), 8.01(2H, d, J 8.4, Ph), 7.91 (1H, d, J 7.6, Ar), 7.50 (1H, td, J 8.4, 1.2,Ar), 7.39 (1H, td, J 8.4, 1.2, Ar), 7.32 (2H, d, J 8.0, Ph), 2.45 (3H,

s, Me). m/z (EI) 225 (57%, [M]þ).2-(3,5-Dimethylphenyl)-1H-benzo[d]imidazole (9a): mp

259–2618C (lit. 260–2638C[34]). nmax (KBr)/cm�1 3382–2504

(NH), 1626 (C¼N), 1564, 1515, 1458, 1369 (C–N), 1258, 1229,

874, 751, 624, 559. dH ([D6]DMSO, 400MHz) 10.00 (1H, br s,NH), 7.66 (1H, dd, J 6.0, 3.6, Ph), 7.56 (4H, s, Ar), 7.29 (1H, dd,J 6.2, 3.6, Ph), 7.23 (1H, s, Ph), 2.32 (6H, s, 2Me). m/z (EI) 222

(12%, [M]þ).2-(3,5-Dimethylphenyl) benzo[d]oxazole (9b): mp 119–

1218C (lit. 121–1228C[35]). nmax (KBr)/cm�1 3051, 2921,2855, 1601 (C¼N), 1551, 1472, 1450, 1376, 1242 (C–O),

1173, 1002, 928, 861, 742, 681, 534, 493. dH (CDCl3,400MHz) 7.91 (2H, s, Ar), 7.80–7.77 (1H, m, Ph), 7.61–7.58(1H, m, Ph), 7.38–7.35 (2H, m, Ar), 7.16 (1H, s, Ph), 2.44 (6H, s,

2Me). m/z (EI) 223 (67%, [M]þ).2-(3,5-Dimethylphenyl) benzo[d]thiazole (9c): mp 74–768C.

nmax (KBr)/cm�1 3072, 3011, 2908, 2855, 1772, 1748, 1683,

1601(C¼N), 1506, 1458, 1431, 1309, 1277, 1184, 1162, 877,842, 754, 724, 685. dH (CDCl3, 400MHz) 8.10 (1H, dd, J 8.0,0.4, Ar), 7.92 (1H, dd, J 8.0, 0.4, Ar), 7.73 (2H, s, Ph), 7.51 (1H,td, J 8.0, 1.2, Ar), 7.40 (1H, td, J 7.8, 1.2, Ar), 7.15 (1H, d, J 0.8,

Ph), 2.43 (6H, s, 2Me). dC (CDCl3, 100MHz) 168.6 (C¼N),154.0 (C–N), 138.7, 134.9 (C–S), 133.4, 132.7, 126.2, 125.3,125.0, 123.1, 121.6, 21.2.m/z (EI) 239 (67%, [M]þ). Anal. Calc.for C15H13NS: C 75.28, H 5.47, N 5.85, S 13.40. Found: C 75.23,H 5.20, N 5.40, S 13.04%.

2-(4-Methoxyphenyl)-1H-benzo[d]imidazole (10a): mp

228–2298C (lit. 228–2308C[36]). nmax (KBr)/cm�1 3325–2400(NH), 1634 (C¼N), 1608, 1506, 1461, 1306 (C–N), 1263, 1189,1021, 839, 750, 616. dH ([D6]DMSO, 400MHz) 8.31 (2H, dd, J

6.8, 2.0, Ar), 7.79–7.76 (2H,m, Ph), 7.51–7.47 (2H, m, Ar), 7.27(2H, d, J 9.2, Ph), 3.90 (3H, s, OMe).

2-(4-Methoxyphenyl) benzo[d]oxazole (10b): mp 95–97 (lit.96–988C[37]). nmax (KBr)/cm

�1 3051, 2982, 2839, 1618 (C¼N),

1605, 1589, 1503, 1453, 1327, 1255, 1243 (C–O), 1169, 1061,1019, 923, 831, 741, 729, 518. dH (CDCl3, 400MHz) 8.21 (2H,dd, J 7.2, 2.0, Ph), 7.77–7.75 (1H,m,Ar), 7.58–7.56 (1H,m,Ar),

7.37–7.32 (1H, m, Ar), 7.04 (2H, dd, J 6.8, 2.0, Ph), 3.91 (3H, s,OMe). m/z (EI) 225 (78%, [M]þ).

2-(4-Methoxyphenyl) benzo[d]thiazole (10c): mp 123–

1248C (lit. 123–1248C[20]). nmax (KBr)/cm�1 2991, 2934,2836, 1603 (C¼N), 1518, 1482, 1434, 1308, 1258, 1223,1171, 1110, 1027, 967, 832, 759, 626, 551. dH (CDCl3,400MHz) 8.06–8.04 (3H, d, J 8.4, Ar, Ph), 7.90 (1H, d, J 8.0,

Ph), 7.49 (1H, t, J 7.6, Ar), 7.37 (1H, t, J 7.2, Ar), 7.02 (2H, d,J 8.4, Ph), 3.90 (3H, s, OMe). m/z (EI) 241 (21%, [M]þ). Anal.Calc. for C14H11NOS: C 69.68, H 4.59, N 5.80, S 13.29. Found:

C 69.33, H 4.50, N 5.42, S 12.95%.(E)-2-Styryl-1H-benzo[d]imidazole (11a): mp 2008C (dec.)

(lit. 2008C[38]). nmax (KBr)/cm�1 3329–2500 (NH), 1644

(C¼N), 1624, 1560, 1447, 1384, 1311 (C–N), 1225, 974, 758,701, 616. dH ([D6]DMSO, 400MHz) 12.45 (1H, br s, NH), 8.00(2H, d, J 7.2, Ar), 7.70–7.30 (5H, m, Ph), 7.18 (2H, d, J 3.2, Ar),

6.87 (1H, d, J 13.2, CH), 6.58 (1H, d, J 13.2, CH). dC ([D6]DMSO, 100MHz) 149.6 (–C¼N), 136.1 (¼C–N), 135.8, 134.8,130.4, 129.4, 128.9, 128.5, 127.4, 123.1, 118.1.

(E)-2-Styryl benzo[d]oxazole (11b): mp 74–768C (lit. 77.5–

788C[39]). nmax (KBr)/cm�1 3060, 3031, 1639 (C¼N), 1575,1532, 1449, 1352, 1234 (C–O), 1176, 964, 931, 861, 840, 761,740, 702, 681, 498. dH (CDCl3, 400MHz) 7.82 (1H, d, J 16.4,

CH), 7.75–7.73 (1H, m, Ph), 7.62 (2H, d, J 8.4, Ar), 7.56–7.53(1H, m, Ph), 7.47–7.40 (3H, m, Ph), 7.39–7.33 (2H, m, Ar), 7.11(1H, d, J 16, CH).

(E)-2-Styryl benzo[d]thiazole (11c): mp 106–1078C (lit.106–1088C[40]). nmax (KBr)/cm�1 3056, 3031, 2921, 2847,1621 (C¼N), 1495, 1432, 1312, 1188, 958, 939, 853, 758,

152 S. Rezazadeh, B. Akhlaghinia, and N. Razavi

725, 689, 666, 433. dH (CDCl3, 400MHz) 8.02 (1H, d, J 8.0, Ar),

7.87 (1H, d, J 8.0, Ar), 7.62–7.53 (3H, m, Ph), 7.50 (1H, td,J 8.2, 1.2, Ar), 7.46–7.38 (5H, m, Ar, Ph, 2CH). m/z (EI) 237(65%, [M]þ).

(E)-2-(4-Chlorostyryl)-1H-benzo[d]imidazole (12a): mp227–229 (lit. 228–2298C[41]). nmax (KBr)/cm�1 3358–2500(NH), 1646 (C¼N), 1571, 1462, 1409, 1311 (C–N), 1229,1086, 973, 817, 755, 624, 502. dH ([D6]DMSO, 400MHz)

8.21 (1H, d, J 16.4, CH), 7.81–7.77 (2H, m, Ar), 7.76 (2H, d,J 8.8, Ph), 7.59 (2H, d, J 8.4, Ph), 7.54–7.50 (2H, m, Ar), 7.36(1H, d, J 16.4, CH). m/z (EI) 253 (3%, [M–1]þ).

(E)-2-(4-Chlorostyryl) benzo[d]oxazole (12b): mp 142–1448C (lit. 144–1458C[42]). nmax (KBr)/cm�1 3051, 1639(C¼N), 1593, 1527, 1487, 1449, 1348, 1286, 1239 (C–O),

1176, 1086, 968, 928, 811, 739, 719, 501. dH (CDCl3,400MHz) 7.76–7.72 (2H, m, CH, Ph), 7.55–7.52 (3H, m, Ph),7.42–7.33 (4H, m, Ar), 7.06 (1H, d, J 16.4, CH).

(E)-2-(4-Chlorostyryl) benzo[d]thiazole (12c): mp 177–

1788C (lit. 177–1788C[43]). nmax (KBr)/cm�1 3051, 3027,2990, 1625 (C¼N), 1589, 1493, 1454, 1403, 1313, 1234,1189, 1089, 1009, 957, 942, 811, 756, 723, 657, 491. dH (CDCl3,

400MHz) 8.02 (1H, d, J 8, Ar), 7.87 (1H, dd, J 8, 0.4, Ar), 7.52–7.46 (4H, m, Ar, Ph), 7.42–7.36 (4H, m, CH, Ph).

2-Benzyl-1H-benzo[d]imidazole (13a): mp 172–1748C (lit.

1758C[44]). nmax (KBr)/cm�1 3234–2851 (NH), 1679 (C¼N),1646, 1600, 1540, 1496, 1453, 1339 (C–N), 1290, 1180, 972,744, 696, 563. dH ([D6]DMSO, 400MHz) 9.53 (1H,m,Ar), 7.47

(1H, t, J 3.2, Ar), 7.32 (5H, m, Ph), 7.26 (1H, d, J 5.6, Ar), 7.14(1H, t, J 4, Ar), 3.61 (2H, s, CH2). m/z (EI) 208 (2%, [M]þ).

2-Benzyl benzo[d]oxazole (13b): mp 27–288C (lit. 288C[45]).nmax (neat)/cm

�1 3084, 3062, 3031, 2929, 1666, 1614 (C¼N),

1569, 1495, 1455, 1425, 1348, 1273, 1241 (C–O), 1140, 1104,1002, 955, 841, 747, 765, 721, 695. dH (CDCl3, 400MHz) 7.72–7.70 (1H, m, Ar), 7.50–7.47 (1H, m, Ar), 7.42–7.40 (2H, m, Ar),

7.39–7.35 (2H,m, Ph), 7.33–7.30 (3H,m, Ph), 4.30 (2H, s, CH2).2-Benzyl benzo[d]thiazole (13c): mp 157–1588C (lit. 158–

1608C[46]). nmax (KBr)/cm�1 3061, 3029, 2949, 2923, 2847,

1723, 1601(C¼N), 1516, 1494, 1454, 1435, 1311, 1242, 1107,1061, 861, 759, 729, 703, 639, 436. dH (CDCl3, 400MHz) 8.21(1H, d, J 8.0, Ar), 7.82 (1H, d, J 8.0, Ar), 7.49–7.45 (1H, m, Ar),7.41–7.30 (6H, m, Ph, Ar), 4.46 (2H, s, CH2).

2-(4-Methoxybenzyl) benzo[d]oxazole (14b): mp 43–458C.nmax (KBr)/cm�1 3035, 3007, 2966, 2928, 2904, 2833, 1899,1772, 1736, 1612 (C¼N), 1566, 1512, 1455, 1441, 1303, 1247

(C–O), 1179, 1140, 1029, 816, 743, 551. dH (CDCl3, 400MHz)7.70 (dd, 1H, J 6.2, 4, Ar), 7.48 (dd, 1H, J 5.8, 4, Ar), 7.33–7.28(4H, m, Ar, Ph), 6.91 (2H, d, J 8.4, Ph), 4.23 (2H, s, CH2), 3.81

(3H, s, OMe). dC (CDCl3, 100MHz) 165.0 (–C¼N), 158.8(¼C–OMe), 150.6 (¼C–O), 141.3 (¼C–N), 130.0, 126.7,124.6, 124.1, 119.8, 114.2, 110.4, 55.2 (OCH3), 34.4 (CH2).

m/z (EI) 239 (62%, [M]þ). Anal. Calc. for C15H13NO2: C 75.30,H 5.48, N 5.85. Found: C 74.90, H 5.18, N 5.19%.

2-Benzhydryl-1H-benzo[d]imidazole (15a): mp 209–2118C(lit. 210–2128C[17a]). nmax (KBr)/cm

�1 3252–2500 (NH), 1728,

1679, 1609 (C¼N), 1491, 1454, 1425, 1388 (C–N), 1270, 1172,1070, 1029, 753, 743, 701. dH ([D6]DMSO, 400MHz) 12.38(1H, br s, NH), 7.54–7.52 (1H, m, Ar), 7.43 (1H, m, Ar),

7.36–7.31 (8H, m, Ar, Ph), 7.27–7.22 (2H, m, Ph), 7.16–7.13(2H, m, Ph), 5.74 (1H, s, CH).

2-Benzhydryl benzo[d]oxazole (15b): mp 67–698C (lit.

69.5–70.58C[47]). nmax (KBr)/cm�1 3060, 3031, 2921, 1605(C¼N), 1563, 1492, 1449, 1236 (C–O), 1154, 1033, 1004,933, 867, 744, 696, 645, 473. dH (CDCl3, 400MHz) 7.79–7.76

(1H, m, Ar), 7.53–7.51 (1H, m, Ar), 7.39–7.29 (12H, m, Ar, Ph),

5.81 (1H, s, CH). m/z (EI) 285 (12%, [Mþ]).2-Benzhydryl benzo[d] thiazole (15c): mp 78–798C (lit.

78–798C[48]). nmax (KBr)/cm�1 3060, 3023, 2921, 2851, 1956,

1593 (C¼N), 1492, 1448, 1431, 1310, 1248, 1180, 1140, 1127,1025, 887, 762, 723, 702, 600. dH (CDCl3, 400MHz) 8.06 (1H,d, J 8.4, Ar), 7.84 (1H, d, J 8.4, Ar), 7.49 (1H, td, J 8.0, 1.2, Ar),7.40–7.28 (11H, m, Ar, 10Ph), 5.99 (1H, s, CH). m/z (EI) 301

(40%, [M]þ).2-(Heptadec-8-enyl) benzo[d]oxazole (16b): Liquid (lit.[47]).

nmax (neat)/cm�1 3056, 3004, 2925, 2853, 1615 (C¼N), 1572

(C¼C), 1456, 1374, 1242 (C–O), 1147, 1002, 928, 837, 744. dH(CDCl3, 400MHz) 7.70–7.67 (1H, m, Ar), 7.50–7.48 (1H, m,Ar), 7.32–7.30 (2H,m,Ar), 5.37–5.34 (2H,m, –CH¼CH–), 2.94

(2H, t, J 8, a to benzoxazole ring), 2.03–2.02 (4H, m,–CH2CH¼CHCH2–), 1.94–1.87 (2H,m,b to benzoxazole ring),1.44–1.28 (20H, m, chain CH2), 0.89 (3H, t, J 6.8, CH3).

2-Heptadecyl-1H-benzo[d]imidazole (17a): mp 87–888C(lit. 88–908C[49]). nmax (KBr)/cm�1 3317–2508 (NH), 1648(C¼N), 1531, 1470, 1370 (C–N), 1225, 894, 857, 744, 624. dH([D6]DMSO, 400MHz) 12.17 (1H, br s, NH), 7.44 (2H, s, Ar),

7.09 (2H, s, Ar), 2.77 (2H, t, J 6.8, a benzoimidazole ring), 1.76–1.72 (2H, m, b benzoimidazole ring), 1.28–0.95 (28H, m, CH2

chain), 0.83 (3H, t, J 6.8, CH3). m/z (EI) 356 (20%, [M]þ).2-Heptadecyl benzo[d]oxazole (17b): mp 53–558C (lit.

558C[50]). nmax (KBr)/cm�1 3056, 2953, 2920, 2849, 1614(C¼N), 1569, 1470, 1456, 1385, 1241 (C–O), 1142, 1111,

1008, 943, 898, 836, 746, 719. dH (CDCl3, 400MHz) 7.70–7.67 (1H, m, Ar), 7.51–7.47 (1H, m, Ar), 7.33–7.28 (2H, m, Ar),2.94 (2H, t, J 7.6, a benzoxazole ring), 1.94–1.86 (2H, m, bbenzoxazole ring), 1.46–1.27 (28H, m, CH2 chain), 0.90 (3H, t,

J 6.4, CH3). m/z (EI) 357 (27%, [M]þ).2-Heptadecylbenzo[d]thiazole (17c): mp 52–538C (lit.

538C[51]). nmax (KBr)/cm�1 3076, 2956, 2918, 2848, 2553,

1704 (C¼N), 1506, 1466, 1315, 1237, 1160, 1090, 890, 764,728, 628. dH (CDCl3, 400MHz) 8.00 (1H, d, J 8.0, Ar), 7.85 (1H,d, J 8.0, Ar), 7.46 (1H, td, J 8.0, 1.2, Ar), 7.36 (1H, td, J 8.0, 1.2,

Ar), 3.13 (2H, t, J 7.6, a benzothiazole ring), 1.93–1.85 (2H, m,b benzoimidazole ring), 1.49–1.27 (28H, m, CH2 chain), 0.90(3H, t, J 6.8, CH3). m/z (EI) 373 (19%, [M]þ).

2-(Thiophen-3-yl)-1H-benzo[d]imidazole (18a): mp 298–

3008C (lit. 3008C[52]). nmax (KBr)/cm�1 3272–2528 (NH),1649 (C¼N), 1597, 1528, 1448, 1428, 1315 (C–N), 1272,1115, 988, 878, 742, 604. dH ([D6]DMSO, 400MHz) 12.87

(1H, br s, NH), 8.26–8.25 (1H, m, thiophen), 7.79–7.78 (1H, m,thiophen), 7.74–7.72 (1H, m, thiophen), 7.56 (2H, m, Ar), 7.19–7.17 (2H, m, Ar). m/z (EI) 200 (85%, [M]þ).

2-(Thiophen-3-yl) benzo[d]oxazole (18b): mp 107–1088C(lit. 1088C[53]). nmax (KBr)/cm�1 3088, 1616 (C¼N), 1576,1450, 1405, 1276, 1241 (C–O), 1176, 1055, 1008, 935, 863,

801, 742, 714, 600. dH (CDCl3, 400MHz) 8.22 (1H, dd, J 3.2,1.2, thiophen), 7.82 (1H, dd, J 5.0, 1.2, thiophen), 7.78–7.76(1H, m, Ar), 7.59–7.56 (1H, m, Ar), 7.48 (1H, dd, J 5.0, 3.2,thiophen), 7.39–7.34 (2H, m, Ar). dC (CDCl3, 100MHz) 159.7

(–C¼N), 150.3 (¼C–O), 141.9 (¼C–N), 129.2, 128.0, 127.0,126.6, 125.0, 124.6, 119.9, 110.4.

2-(Thiophen-3-yl) benzo[d]thiazole (18c): mp 98–998C (lit.

99–1008C[46]). nmax (KBr)/cm�1 3080, 3051, 2917, 2851, 1540

(C¼N), 1474, 1432, 1372, 1312, 1238, 1188, 1164, 1075, 995,892, 870, 839, 785, 766, 731, 652. dH (CDCl3, 400MHz) 8.06

(1H, d,J8.4,Ar), 8.04 (1H,dd, J2.8, 1.2,Ar), 7.90 (1H,d, J8,Ar),7.73 (1H, dd, J 5, 1.2, Ar), 7.50 (1H, td, J 8, 1.2, thiophen), 7.45(1H, dd, J 5.2, 3.2, thiophen), 7.40 (1H, td, J 7.6, 0.8, thiophen).

Synthesis of 1,3-Benzazoles 153

2-(Pyridin-4-yl)-1H-benzo[d]imidazole (19a): mp 206–

2088C (lit. 207.3–2088C[54]). nmax (KBr)/cm�1 3382–2524(NH), 1634, 1614 (C¼N), 1544, 1429, 1318 (C–N), 1237,1015, 967, 835, 767, 750, 698, 559. dH ([D6]DMSO,

400MHz) 12.70 (1H, br s, NH), 8.76 (2H, d, J 6, Py), 8.11(2H, d, J 6Hz, Py), 7.66 (2H, dd, J 5.6, 3.2, Ar), 7.26 (2H, dd,J 6.0, 3.2, Ar). dC ([D6]DMSO, 100MHz) 150.9 (–C¼N), 149.2(–C¼N pyridine ring), 137.6 (¼C–N), 123.3, 120.7, 119.1.

2-(Pyridin-4-yl) benzo[d]oxazole (19b): mp 125–1278C (lit.127–1288C[55]). nmax (KBr)/cm�1 3047, 2958, 2929, 2851,1728, 1687, 1614 (C¼N), 1594, 1540, 1449, 1411, 1346, 1250

(C–O), 1057, 927, 833, 811, 751, 703, 690, 516. dH (CDCl3,400MHz) 8.85 (2H, s, Py), 8.12 (2H, d, J 6, Py), 7.86–7.84 (1H,m, Ar), 7.67–7.65 (1H, m, Ar), 7.48–7.42 (2H, m, Ar).

6-Methyl-2-phenyl benzo[d]oxazole (20b): mp 90–928C (lit.90–938C[56]). nmax (KBr)/cm

�1 3060, 3023, 2855, 1736, 1616(C¼N), 1553, 1484, 1447, 1336, 1290, 1249 (C–O), 1172, 1127,1051, 1020, 922, 832, 808, 700, 686, 604. dH (CDCl3, 400MHz)

8.27–8.24 (2H,m, Ph), 7.66 (1H, d, J 8.0, Ar), 7.55–7.52 (3H,m,Ph), 7.40 (1H, s, Ar), 7.19 (1H, d, J 8.0, Ar), 2.53 (3H, s,Me).m/z(EI) 209 (13%, [M]þ).

Supplementary Material

Details of analysis of 1,3-benzazoles derivatives are availableon the Journal’s website.

Acknowledgements

The authors gratefully acknowledge partial support of this study by Ferdowsi

University of Mashhad Research Council (Grant No. p/3/25246).

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