the preparation and oxidation of disulfides as a route to sulfone-sulfides

The preparation and oxidation of disulfides as a route to sulfone-sulfides

T E R E U C ~ PATRICK A H E R ~ . HARVEY OWEY FOYG, RICHARD FRAUCIS LAUGLER,'

A N D PETER MICHAEL MA SO^ Chetnlstrt Depnrtment, Dulhousle U t z~cer~~ t \ , Hnl~fnx , N S , Cat~udn B3H4J3

Received December 3 , 1979

TERENCE PATRIC K AHERN. HARVEY OWEN F o ~ G . RICHARD FRANCIS LANGLER. and PETER MICHAEL MA SO^. Can. J. Chem. 58, 878 (1980).

Mercaptidelaikoxide competition in substitution and addition reactions is discussed as it applies to the preparation of disulfides. Oxidation of an asymmetric disulfide with H 2 0 2 is shown to exhibit high regioselectivity which may be rationalized in the same terms employed for other sulfide oxidations. viz. substituent electron withdraming ability (X,) and steric effects.

TERENCE PATRICK AHERN. HARVEY OWEY FOYG, RICHARD FRANCIS LAYGLER et PETER MICHAEL MASON. Can. J. Chem. 58, 878 (1980).

On discute de la competition existant entre les thiolates et les alcoolates 10:s des reactions d'addition et de substitution, telles qu'elles sont appliquees a la preparation des disulfures. On a montre que l'oxydation d'un disulfure asymetrique par H 2 0 2 est hautement regioselective et qu'elle peut &re expliquee comme dans le cas des oxydations d'autres sulfures. par I'effet des substituants electroattracteurs (X,) et des effets steriques.

[Traduit par le journal]

Introduction In connection with our work on the chlorinolyses

of sulfur compounds (I-lo), we have become in- terested in the preparation of p-sulfone-sulfides. These compounds permit the assessment of sul- fonyI moieties as directing groups in asymmetric sulfide chlorinations (3). We have recently reported (2) the results generated by our approach to sulfone-sulfide synthesis via mercaptosulfone intermediacy.

cblorosulfides may be cleanly condensed in an alcoholic medium (41, eq. [ I ] illustrates one possible complication.

CH,SH [ I ] CH3S02CH2SCHC1CH3 +

CH30H /CH,ONa 1

CH3S02CH2SCHCH3 + CH3S02CH2SCHCH3 I SCH,

I OCH,

2 (22%) 3 (78%)

The present reporr details On the prep- The results shown in eq. [ I ] can be rationalized by aration and oxidation of disulfides with a view to presuming an S,I mechanism which becomes do- obtaining the corresponding P-sulfone-sulfides. minant due to the enhanced stability of an aikyl The conversion of a disulfide to a P-sulfone-sulfide substituted sulfenium ion over an unsubstituted requires the intermediacy of a P-sulfoxide-sulfide. sulfenium ion Consistent with this proposal. 6 is While there are a variety of reagents (1 1-16) which formed, without in acetone. permit the conversion of disulfides to p-sulfoxide- sulfides, very few reagents will accbmplish the PhSNa conversion of a sulfoxide-sulfide to a sulfone- P I CH~SOZCHZSCHC~CH~ sulfide. I

CH3S02CH2SCHCH3 Results and Discussion I

Disulfides may be prepared by condensation of a mercaptan with an aldehyde or ketone (17-19) or by base catalyzed condensation of a mercaptan and an ol-chlorosuifide .'

Although some mercaptide anions and a-

'Enquiries should be directed to Dr. R. F. Langler, Chemistry Department. Mount Allison University, Sackville, N.B., Canada EOA 3C0.

2The desired cr-chlorosulfide may be prepared by chlorination of the desired sulfide with sulfuryl chloride or N- chlorosuccinimide, provided due consideration is given to substituent electronegativities. (3).

In a related Michael addition reaction (eq. [3]) a similar complication has been observed.

PhSH [3] CH2=CH-C02CH3 b

CH,0H/CH30Na

The results in eq. [3] may be rationalized by presuming that mercaptide anion addition is rever-

W8-4042/80/090878-06$0 I .OOlO @ 1980 National Research Council of CanadaIConseil national de recherches du Canada

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AHERK ET AL. 879

sible while alkoxide anion addition is not.3 In any case it is clear that alcoholic media may present unwelcome complications in these condensation reactions.

We have selected the svmmetric disulfide 7 to begin our examination of disulfide oxidations

The formation of 8 from oxidation of 7 as shown in eq. [4] is rather surprising since peroxidic oxidations normally give exclusively disulfoxides as outlined in eq. [5].

The twofold oxidation of 9 ~ r o d u c e d no detectable amount of sulfone-sulfide in accord with a previous study of sulfide oxidations (22). Clearly, the oxidation of disulfides with peroxides is an unsuitable approach to the preparation of sulfone- sulfide^.^

Sodium permanganate in aqueous dioxane has been reported (23) to permit the selective oxidation of sulfoxides in preference to sulfides. In that paper some difficulty was encountered with solvent oxidation. We have elected to employ potassium permanganate in aqueous TMFS as a reagent system with somewhat improved availability and stability. To test this modified reagent system we have pre- pared6 and oxidized the sulfoxide-sulfide 11. The results are depicted in Scheme 1. The conversion of 11 to 13 illustrates the importance of the reaction conditions.

It was our objective to examine the oxidation of 6 which could, in principle. form a pair of re- gioisomeric sulfone-sulfoxide-sulfides each of which would exist as a pair of diastereomers. We have chosen to begin this portion of the work by examining a simpler system in order to establish a way to distinguish between regioisomers and dia- stereorners. We, therefore, subjected the sulfone- sulfide 1 to oxidation with one equivalent of tn- chloroperbenzoic acid (mCPBA) as shown in

3The sulfide ester 4 was prepared in good yield when the reaction was conducted in pyridine (2).

4A paper has appeared (21) which reports that KMnO, in cold acetone furnishes sulfone-sulfides from symmetric disulfides. Reaction times are 8-10 days.

5Even dioxane freshly distilled from MMnO, reacted significantly faster with permanganate than THF.

6Sulfoxide-sulfides may also be obtained from sulfinate esters (24).

Scheme 2. Nuclear magnetic resonance indicated that the sulfone-sulfoxide 14' was an equimolar mixture of two compounds. Oxidation of 14 furnished the homogeneous disulfone 15 in greater than 90% yield, thereby establishing that 14, as expected (25-271, was a mixture of diastereomers.

We were now prepared to examine the oxidation of 4 to assess regioselectivity in that reaction. While the problem of regioselectivity in 1.3- disulfide oxidations does not appear to have been scrutinized previously, that of regioselectivity in 1.2-disulfide oxidations has been.

Bhattacharya and Hortmann (28) have reported the disulfide oxidations shown in eq. [6] to be re- giospecific.

They have concluded that "oxidation appeared to occur (in the absence of steric effects) at the sulfur atom farthest removed from the relatively

more electron withdrawing group." Oxidation d 1.2-disulfides, as these authors point out. may pro- ceed through 1,2-disulfoxides (29). In the closely related sodium metaperiodate oxidations of 1,2- disulfides Oae et (11. (30) report no indication of 1,2-disulfoxide formation. These same factors, viz. steric effects and the electron withdrawing ability of substituents. have been cited to rationalize peroxydisulfate oxidations of simple sulfides (31).

Application of these factors to 6 leads to the expectation that oxidation should occur with high regioselectivity, at the sulfur bearing the phenyl group on the grounds that (i) a mesylmethyl group is more electronegative than a phenyl group (X,CH,SO,CH, = 2.85, X,Ph = 2.49 (3)), and (ii) the central sulfur atom is much closer to the bulky mesyl groupqhan is the thiophenyl sulfur atom.

Oxidation of 6 with an equivalent of H,O, afforded a mixture 16 of two compounds which dis- played different chemical shifts for all corresponding non-aromatic protons, e.g., two doublets (all lines approximately equal in intensity) appeared at 6 1.23 and two singlets appeared at 6 3.03 in the nmr spectrum. Oxidation of the mixture with MMnO,/H,O/THF afforded an homogeneous disulfone-sulfide, tentatively assigned structure 17 in about 50% yield. Crude 16 from another run was

'Compound 14 was shown to be free of unreacted P and disulfone 15 by the addition of authentic samples of each to 14 which gave rise to the expected new signals in the nmr.

8The nature of the steric effect of the mesyl (or methylsul- fonyl) group has been discussed previously ( 1 ) .

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CAN. J. CHEM. VOL. 58 . 1980

30%H 0 (CH,02CCH2S)2CH2 A C H 3 0 2 C C H 2 . S O . C H 2 S C H 2 C 0 2 C H ,

9 11

( C H , 0 2 C C H 2 S 0 2 ) 2 C H 2 CH,02CCH2. SO,. C H 2 S C H 2 C 0 2 C H ,

13 12 SCHEME 1

m C P B A CH,. SO2. CH2SCHCICH, CH, . SO,. C H 2 . S O . CHCICH,

P CHCI, 14

1 30'7' H 2 0 2 1 CH, . SO2. CH2SCHSPh + C H , SO2. C H 2 S C H . S O . Ph

6 16

subjected to column chromatography which furnished a homogeneous sample of one diastereomer. Permanganate oxidation of the homogeneous diastereomer furnished the same disulfone-sulfide 17 in essentially the same yield as obtained from the diastereomeric mixture (oide Scheme 3). These results establish that 16 was indeed a diastereomeric mixture and that oxidation of 6 was highly regioselective.

The first evidence concerning which sulfur atom of 6 was oxidized to yield 16 was obtained from the mass spectrum of 16. A moderate intensity ion was observed at mle 125 (relative abundance ca. 50%) in accord with the presence of a phenylsulfinyl group. The mass spectrum of 17 showed the base peak at mle 153 (Mt - PhSO,). The loss of substituted sulfonyl groups as neutral fragments from molecular ions has been amply precedented (32-34). Furthermore, the arokatic regions In the nmr spectra of 6 and 16 show broad singlets whereas the nmr of 17 shows two distinct aromatic

signals in accord with the presence of an electronegative SO, group attached directly to the phenyl ring.

A brief deuterium exchange experiment furnished polydeuterated 17. The nmr and mass spectrum indicated about 78% exchange at C4 and 11% exchange at C2. This result is clearly inconsistent with the alternative disulfone-sulfide structure for 17. The selectivity in the exchange experiment on 17 could be rationalized on the basis of a slightly greater acidity for the methylene protons than for the methine proton.

In conclusion we have found that ji) nucleophilic competitions make substitution and addition reactions in alcohols unreliable when mercaptide anions are the intended nucleophiles, and (ii) regioselectivity in a I ,3-disulfide oxidation appears to be subject to the same considerations advanced for 1.2-disulfide oxidations, i.e.. the electron withdrawing ability (Pic',) of subsrituents and steric effects.

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A H E R N ET AL. 88 1

Experimenbl General

The ir spectra were recorded on a Perkin-Elmer 237B grating spectrophotometer. The nmr spectra were obtained on a Varian T60 instrument using TMS as the internal standard. The mass spectra were recorded on a Dupont-CEC model 21-104 mass spectrometer. Samples were directly introduced using an all glass probe and the spectra run at 30 eV with a source temperature of 150°C. Melting points were determined on a Fisher-Johns melting point apparatus and are uncorrected.

Reaction of I with Sodium itlethyl Merraptide in Metizcinol Sodium metal (0.155 g) was dissolved in methanol (25 mL)

and the solution cooled to 5°C. Methanethiol(3 mL) was slowly distilled into the solution. The a-chlorosulfide l(1.236 g) (3) was added and the reaction mixture stirred at ambient temperature for 24 h. Water (25 mL) was added and the resultant-mixture washed with chloroform (five 50 mL aliquots). The combined organic layers furnished a mixture of the sulfone-sulfide-ether 3 and the sulfone-disulfide 2. The mixture was chromatographed on silicagel (100 g) with diethyl ether elution (1W mLaliquots).

Fraction 3 (108.2 mg) was sulfone-disulfide 2. ir (CHCl,): 1315and 1110 cm-';nmr(CDCI,)G: 4 . 4 6 ( 1 H . q , J = 6 Hz).4.30 (1W. d. J = 14 Hz), 3.90 ( I N , d . J = 14 Hz). 2.96 (3H. s), 2.03 (3H. s), and 1.60(3H, d. J = 6 Hz); msmle: 200(Mt. 23.9%)and 75 (100%).

Fraction 4 (194.6 mg) was an equimolar mixture of 2 and 3. Fractions 5-8 were combined and concentrated affording the sulfone-sulfide-ether 3 (585 mg), ir (CHCI,): 1315 and 11 15 cm-'; nmr (CDC1,)G: 5.03 ( I H , q. J = 6 Hz), 3.96(2H. s), 3.36(3H, s). 3.00(3H. s) ,and 1.53(3W,d, J = 6 H z ) ; m s m l e : 184(Mt, 1.556) and 59 (1007~).

Reaction of (Methyl Ac.r.ylare and Sodiurn Thiophenoxide in Methanol

Sodium metal (4.224 g) was dissolved in methanol (200 mL) and benzenethiol (19.8 g) added. The solution was cooled and methyl acrylate (15.62 g) in methanol (50 mL) was added dropwise over 0.5 h. The reaction mixture was refluxed 1 h. Water (250 mL) was added and the resultant mixture washed with methylene chloride (four 200 mL aliquots). The combined organic layers afforded a mixture of the ether-ester 5 and the sulfide-ester 4. The mixture was rectified at reduced pressure affording 5 (9.949 g. bp 32-34"C/3 Torr) and 4 (4.524 g).

The sulfide-ester 4 was identical with previously described material (2).

The ether-ester 5 had ir (CHCI,): 1730 c m ' ; nmr (CDCI,) 6: 3.73 (3H. s). 3.73 (2H, t), 3.39 (3H. s) and 2.60 (2H. t); ms rnle: 118 (My, 28.5%). 59 (28.5%), and 45 (100%).

triethylamine (10 mL). and water (I0 mL). After stirring overnight the reaction mixture was diluted with chloroform, acid washed. dried. and rectified at reduced pressure affording acid free disulfide (7.76 g. bp 144"C/5 Torr).

The disulfide (4.661 g) was dissolved in dioxane (50 mL) and H , 0 2 ( 3 0 9 , 2.870 g) added. The reaction mixture was refluxed for 0.5 h, after which it was concentrated and chromatographed on silica gel (400 g). Elution of the column with chloroform (100 mL aliquots) furnished the sulfone-sulfide 8 (0.438 g) from fractions 20-28. After recrystallization from 95% ethanol the sulfone-sulfide had mp 109-1 11°C and R f 0.25 (with chloroform development); ir (CHC1,): 1320 and 1120 cm-I; nmr (CDCL,) G: 7.43(5H,s).4.86(1H,s).2.86(3H.s).and2.46(3H,s);msm/': 137 (100%) and 121 (25%). Anal. calcd. forC,H120,S2: C 49.97. H 5.59; found: C 50.17. H 5.48.

Peroxidation of 9 The disulfide-diester 9 (5.007 g) (35) was dissolved in dioxane

(25 mL) and H 2 0 , (3@%, 2.522g) was added. The reaction was refluxed for 0.5 h and the solvent evaporated. The residue was recrystallized from methanol affording disulfoxide-diester 10 (3.347 g, mp 90-94°C); ir (CHCl,): 1740 and 1050 cm-I; nmr (CDCI,)G: 4.36(6H. m)and 3.86(6H. s): mstnle: 106(16.9%). 74 (33.8%), 59 (61.9%). and 45 (100%). Anal. calcd. for C,Hl,O,S,: C 32.80. H 4.71;foundC 32.76. H 4.59.

Preparation of 11 The disulfide-diester 9 (5.005 g) (35) was dissolved in dioxane

(25 mL) and H 2 0 2 (30%. 2.522 g) was added. The reaction was refluxed for 0.5 h and the solvent evaporated. The crude product was chromatographed on silica gel (350 g) employing 9: l diethyl ether - methanol (100 mL aliquots) as eluent. Fractions 13-17 were combined and concentrated affording clean diester- sulfoxide-sulfide 11 (2.376 g) as an oil; ir (CHCl,): 1745. 1740. and 1050 cm-I: nmr (CDCI,) 6 : 4.30 ( I H . d , J = 12 Hz). 4.20 ( l H , d , J = 12 Hz), 3.90 ( l H , d , J = 12 Hz). 3.80 ( I H , d , J = 12 Hz), 3.80 (3H. s), 3.76 (3H, s). and 3.57 (2H. s); ms tnle: 119 (84.7%), 91 (23.6%), and 45 (100%).

Permanguni~ft~ Oxidutiotl o f l l in THF The diester-sulfuxide-sulfide 11 (1.000 g) in T H F (5 mL) was

added to a mixture of KMnO, (0.444 g) in 2m vlv aqueous T H F (100 mL). The reaction mixture was stirred at ambient temperature for 10 min. Water (100 mL) was added and the resultant mixture washed with chloroform (four 100 mL aliquots). The combined organic layers were dried and concentrated. The crude diester-sulfone-sulfide (0.962 g) was chromatographed on silica gel employing diethyl ether (50 mL fractions) as eluent. Fractions 7-12 were combined and concentrated affording clean

Preparation of 6 diester-sulfone-sulfide 12 (0.680 g) as an oil; ir (CHCI,). 1750, A solution of sodium thiophenate (0.912 g) in acetone (3 mL) 1328% and 1110 cm-'; nmr (CDCl,) 6: 4.37 (2H, $1, 4.33 (2H. 31,

was added to a solution of the chlorosulfone-sulfide 1 (1.000 g) 3.83 (3H. s). 3.77 (3H, s), and 3.67 (2H. s); ms mle: 197 (7.5%). (3) in acetone (9 mL) and the reaction mixture stirred at ambient 119 (loo%), 91 (3wo). and 45 (88.6%). temperature for 24 h. Water (25 mL) was added and the resultant mixture washed with chloroform (four 50 mL aliquots). The combined organic layers were dried and concentrated affording crude sulfone-disulfide 6 (1.282 g). The crude product was chromatographed on silica gel (100g) employing 4:l ether-chloroform (50 m L fractions). Fractions 6-8 were combined and concentrated and the residue recrystallized affording clean 6 (0.901 g. mp 40-41°C); ir (CHCI,): 1320 and 1120 c m l ; nmr (CDC1,) 6: 7.30 (5H, broad s). 4.80 ( I H , q . J = 6 Hz). 4.33 ( IH. d , J = 14 Hz), 3.90 ( JH, d. J = 14 Hz), 2.96 (3H, s), and 1.60 (3H. d , J = 6 Hz); ms tnle: 262 (My. 19.6%). 134 (86.0%). 109 (54.2%). and 73 (100%). Anal. calcd. for C,,H,,O,S,: C 45.77.13 5.37; found: C 45.63. H 5.59.

Pero,ridation of 7 The disulfide 7 (10 g) (19) was dissolved in pyridine ( l W mL),

Concersiotz of d l to 13 A solution of the diester-sulfoxide-sulfide 11 (1.003 g) in

chloroform (25 mL) was added to 10% vv/ sulfuric acid in water (35 mL) dropwise over 15 min. During the addition KMnO, (5.024 g) was added in small portions. Upon completion of the additions, the reaction mixture was stirred at room temperature for 1 h. The reaction mixture was cooled and sodium bisulfite added until the mixture became colorless. The layers were sepa- rated and the aqueous layer washed with chloroform. The combined chloroform layers were dried and concentrated affording the diester-disulfone 13 (1.15 g). Upon recrystallization the disulfone 13 had ir (CHCI,): 1750, 1350, and 1120 cm-I; nmr (CDCI,) 6: 5.33 (2H, s), 4.46 (4H. s), and 3.90 (6H, s); ms m/e: 288 (Mt. 13%), 151 (lW%'c), 79 (46.5%), and 74 (60.5%). Other properties were in accord with a previous report (36).

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882 C A N . J . CHEM. VOL. 58, 1980

Preparatiot~ of 14 .4 solution of the chlorosulfone-sulfide 1 (2.241 g) (3) in

chloroform i5OmL) was cooled to -6°C and nz-chloroperbenzoic acid (85%. 2.534g) added in small portions. The ice in the cooling bath was allowed to melt and the reaction mixture was stirred overnight. Chloroform (150 mL) was added and the resultant solution washed with 1% NaOH (two 50 mL aliquots). The organic layer was dried and concentrated. The residue was recrystallized from 95410 ethanol affording diastereomeric chlorosulfone-sulfoxide 14 (0.799 g. mp 78-80°C); ir (CHCI,): 1325. 1150. and 1060 cm-'; nmr (CDCI,) 6: 5.26 (0.5H, q. J = 7 Hz), 5.00 (0.5H. q, J = 7 Hz), 4.33 (2H, broad s). 3.23 (3H, s). and 1.93 (3H. d. J = 7Hz); ms tnle: 141 (12.6%), 127 (11.5%). and 63 (lom).

Oxic/ritiorr of 14 The chlorosulfone-sulfoxide 14 (0.100 E) in glacial acetic acid

(1 mL) was added to a mixture of chromium tnoxide (0.065 g) in glacial acetic acid (2 mL). The reaction mixture was heated to 90-100°C for 0.5 h. Water (15 mL) was added and the resultant mixture washed with chloroform (three 25 mL aliquots). The combined organic layers here ~ a s h e d with 2.5% w/v NaOH (two 25 mL aliquots). dried. and concentrated. The product was hornogeneous chlorodisulfone I5 (by nmr) (0.097 g). Upon recrystallization it was shown to be identical with previously prepared chlorodisulfone 15 (3) by nmr. ir, mp, and mixture mp.

0-ridnti~e Coni.ersion o f 6 to 17 Hydrogen peroxide (30%, 0.432 g) was added to a solution of

the sulfone-disulfide 7 (0.500 g) in dioxane (25 mL) and the solution refluxed for 0.5 h. The solvent was evaporated and the residue chromatographed on silica gel (50 g) employing diethyl ether (50 mL fractions) as eluent. Fractions 5-7 were combined and concentrated affording the disulfone-sulfide 17 (0.137 g. mp 147-148°C): ir (CHCI,): 1320 and 1150 cm-I; nmr (CDCI,) 6: 8.03(2H,m).7.70(3H,m),4.86(1H,q,J=7Hz),4.73(1H.d,J = 14Hz) .3 .90 ( IH ,d , J= 14Hz),3.03(3H,s).and1.50(3H,d, J = 7 Hz); msm/e: 294(Mt. 1.9%). 153(100R). 125(28.2%), and 73 (96.1%). Anol. calcd. for C,,H,,O,S,: C 40.79, H 4.79; found: C40.83. H4.61.

Preparation of 16 The sulfone-disulfide 6 (2.023 g) was added to a solution of

hydrogen peroxide (30%. 0.874 g) in dioxane (100 mL) and the reaction mixture refluxed for 0.5 h. The solvent was evaporated and the residue chromatographed on silica gel (200 g) employing diethyl ether (100 mL fractions) for elution. Fractions 34-36 were combined and concentrated affording one of the diastereomers of 16 as a pure oil (0.317 g): ir (CHCI,): 1320, 1110. and 1060 cm-I; nlnr (CDCI,) 8 : 7.63 (5H. broads). 4.60(1H, q , J = 6 Hz). 4.36(1H. d, J = 14 Hz). 3.90(1H,d. J = 14 Hz), 3.10 (3H. s). and 1.33 (3H. d. J = 6 Hz); ms m/e: 155 (40.3%), 125 (48.3%), 109 (100%). and 73 (32.2%).

The other diastereomer differed principally in its nmr spectrum which was obtained by subtraction of the nmr of the pure diastereo~ner from the nmr of a mixture of diastereomers. the second diastereomer had nmr (CDCI,) 6: 7.53 (SH, s. broad), 4 .43(1H,q . J=6Hz) ,4 ,36(1H,d , J= 14Hz) ,3 .80 (1H,d , J= 14 Hz). 2.96 (3H, s) , and 1.36 (3H, d, J = 6 Hz).

Oxidation of 6 (2 g) furnishes ca. 1 : 2 mixture of diastereomers (1.92 g).

Conbrrsion oj"l6to 17 Both the crude diastereomeric mixture 16 and the purified

diastereomer described above gave essentially the same results outlined below.

The sulfone-sulfoxide-sulfide 16 (0.202 g) in THF (5 mL) was added to potassium permanganate (0.076 g) in 2M v/v aqueous TI-IF(100 mL). The reaction was stirred at ambient temperature

for 10 min. Water (100 mL) was added and the mixture washed with chloroform (four 100 mL aliquots). The organic layers afforded disulfone-sulfide 17 (0.173 g) uhich was homogeneous by tlc and nmr. Recrystallization afforded 17 which was identi- cai with previously obtained inaterial by ir. nmr. mp. and mixture mp.

The authors are indebted to Mr. D. G. Kay and Mr. Z. A . Marini for some technical assistance. We thank Dr. J. H. Kim for running the mass spectra. We are grateful to Dalhousie University for finan- cial support in the form of agrant from the Research Development Fund.

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~ r r a t h m : Pseudozoankhoxanthins from gold coral i . s ,

IPOBER"~ E. SCHWARTZ, MARK B. Y U N K E R , A N D PAUL J . SCHEUER Department of Chemistrq., Unicersity of'Ha,r.aii at Manoa, Honolulrr, HI 96822, U.S.A

A N D

TOR OTTERSEN Deprirttnrnt of Ckerni.stry, Utricersity of Oslo, Blindern, Oslo 3, Norway

(Ref.: Can. J . Chem. 57, 1707 (1979)) Received February 4, 1980

In Table 1, the uv spectral data for compound 5 in MeOH and MeOH-H+ are incorrect. They should read:

Compound Solvent Wavelength. nm (log E)

5 MeOH 425(4.12) 306(4.22) 289(4.22) 259(4.3 1) 224(4.2 1) 5 MeOH-Hi 419(4.23) 291(4.35) 257(4.18) 226(4.18)

In Table 2, compound 4" does not have an NHMe 3H singlet at 6 3.42. In compound 9'. the two overlapping singlets at 6 3.62 and 6 3.54 are not 3W singlets, but rather 6H singlets.

W8-4042/80/090883-01$0 1 .00/0 a1980 National Research Council of CanadaIConseil national de recherches du Canada

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the preparation and oxidation of disulfides as a route to sulfone-sulfides

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