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Synthesis and Catalytic Applications of a Triptycene-Based Monophosphine Ligand forPalladium-Mediated Organic TransformationsLeung, King-Chi; Ishiwari, Fumitaka; Shoji, Yoshiaki; Nishikawa, Tsuyoshi; Takeda, Ryohei;Nagata, Yuuya; Suginome, Michinori; Uozumi, Yasuhiro; Yamada, Yoichi M. A.; Fukushima,TakanoriPublished in:ACS Omega

DOI:10.1021/acsomega.7b00200

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Citation for published version (APA):Leung, K-C., Ishiwari, F., Shoji, Y., Nishikawa, T., Takeda, R., Nagata, Y., Suginome, M., Uozumi, Y.,Yamada, Y. M. A., & Fukushima, T. (2017). Synthesis and Catalytic Applications of a Triptycene-BasedMonophosphine Ligand for Palladium-Mediated Organic Transformations. ACS Omega, 2(5), 1930−1937.https://doi.org/10.1021/acsomega.7b00200

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Synthesis and Catalytic Applications of a Triptycene-BasedMonophosphine Ligand for Palladium-Mediated OrganicTransformationsFranco King-Chi Leung,†,‡ Fumitaka Ishiwari,† Yoshiaki Shoji,† Tsuyoshi Nishikawa,§ Ryohei Takeda,§

Yuuya Nagata,§ Michinori Suginome,§ Yasuhiro Uozumi,‡,∥ Yoichi M. A. Yamada,*,‡

and Takanori Fukushima*,†

†Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta,Midori-ku, Yokohama 226-8503, Japan‡RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako 351-0198, Japan§Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura,Nishikyo-ku, Kyoto 615-8510, Japan∥Institute for Molecular Science and The Graduate School for Advanced Studies, Myodaiji, Okazaki 444-8787, Japan

*S Supporting Information

ABSTRACT: 1-Methoxy-8-(diphenylphosphino)triptycene (1), featuringhigh structural rigidity and steric bulkiness around the phosphinefunctionality, was synthesized as a new chiral monophosphine ligand fortransition metal-catalyzed reactions. In the presence of 5−10 mol ppm (i.e.,0.0005−0.001 mol %) Pd(OAc)2 and 1 (2 equiv for Pd), Suzuki−Miyauracross-coupling reactions of aryl bromides and arylboronic acids proceededeffectively under mild atmospheric conditions to give the correspondingbiaryl compounds in a high yield. The single-crystal X-ray analysis of aPd(II) complex of 1 revealed its coordination structure, in which twohomochiral molecules form a dimer, suggesting that triptycene couldprovide a chiral environment for asymmetric organic transformations. Infact, optically active 1 obtained by optical resolution showed goodenantioselectivity in the palladium-catalyzed asymmetric hydrosilylation ofstyrene, which represents, for the first time, the asymmetric catalytic activityof triptycene-based monophosphine ligands.

■ INTRODUCTION

Triptycene is a propeller-shaped molecule composed of three120°-oriented phenylene blades (Figure 1a).1 Along with thishigh molecular symmetry, triptycene provides a large freevolume around the aromatic skeleton. These structural featuresof triptycene have inspired chemists to develop organic,2−4

polymeric,5 and supramolecular6,7 functional materials, whichhave mainly focused on the use of the free volume in terms ofhost−guest chemistry. For this purpose, a large number oftriptycene derivatives with functional groups at the metaposi-tions of the bridgehead carbons (e.g., 2-, 3-, 6-, 7-, 14-, and 15-positions) have been synthesized. Meanwhile, regiospecificfunctionalization of triptycene at the three ortho positions (i.e.,1-, 8-, 13- or 4-, 5-, 16-positions) of the bridgehead carbon canforce the attached functional groups to assemble in proximity toeach other at a distance of approximately 4.5 Å (Figure 1b).Although this type of triptycene is relatively rare, itsstereochemistry would be useful in the design of ligands fortransition metal catalysis.8,9

To date, several 1,8-substituted triptycene-based bisphos-phine ligands have been developed, so as to take advantage ofthe particular bite angle and geometry of chelation.8 In thiscontext, 1,8-substituted triptycene-based monophosphineligands should also be interesting because sterically bulky andrigid monodentate ligands generally show a high catalyticactivity for various transition metal-catalyzed reactions.10

Furthermore, when different functional groups are incorporatedinto these positions, the resultant substituted triptycene shouldbecome chiral (Figure 1c). However, to the best of ourknowledge, only one previous report has described thesynthesis of a triptycene-based chiral monophosphine ligand,and the catalytic activity of its transition metal complex has notbeen investigated.9 Here, we report the synthesis of 1-methoxy-8-(diphenylphosphino)triptycene (1, Figure 1c, Scheme 1) as aprototype of a triptycene-based chiral monophosphine ligand.

Received: February 20, 2017Accepted: April 28, 2017Published: May 9, 2017

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© 2017 American Chemical Society 1930 DOI: 10.1021/acsomega.7b00200ACS Omega 2017, 2, 1930−1937

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Using Pd-catalyzed Suzuki−Miyaura cross-coupling and asym-metric hydrosilylation as model reactions, we demonstrate forthe first time the catalytic activity of a monophosphineconsisting of a sterically bulky and structurally rigid triptycenescaffold.

■ RESULTS AND DISCUSSIONSynthesis of 1-Methoxy-8-(diphenylphosphino)-

triptycene (1). In the light of the structures of axially chiralmonodentate phosphine (MOP) ligands11 and a simplegeometrical model (Figure 1d), we designed monophosphineligand 1 (Figure 1c), which was successfully synthesized from1,8-dihydroxytriptycene (2)13 using procedures similar to thosefor MOP ligands11,12 (Scheme 1). Thus, compound 2 was

reacted with trifluoromethanesulfonic anhydride (4.0 equiv) in1,2-dichloroethane at 60 °C in the presence of pyridine (8.0equiv) to give 1,8-bis(trifluoromethanesulfonyloxy)triptycene(3) in 75% yield. Monophosphinylated triptycene 4 wasobtained as a racemic mixture in 90% yield through the reactionof 3 with diphenylphosphine oxide (2.0 equiv) in the presenceof Pd(OAc)2 (5.0 mol %) and 1,4-bis(diphenylphosphono)-butane (5.0 mol %) in dimethyl sulfoxide (DMSO) at 100 °C.Upon treatment with NaOH, the triflate group of 4 wasconverted into a hydroxy group, which was subjected tomethylation with MeI (2.9 equiv) in the presence of K2CO3(2.9 equiv) to give 6 in 89% yield (two steps). The phosphineoxide group of 6 was reduced by HSiCl3 in the presence oftriethylamine in toluene at 120 °C, to allow the isolation of 1 in90% yield. All compounds were unambiguously characterizedby 1H and 13C NMR spectroscopies, infrared (IR) spectrosco-py, and high-resolution atmospheric pressure chemicalionization time-of-flight (APCI-TOF) mass spectrometry(Figures S5−S16).Many attempts to achieve the optical resolution of 1 using

chiral high-performance liquid chromatography (HPLC) undervarious conditions were not successful. Instead, we found thatchiral HPLC (CHIRAL ART Amylose-SA column, CHCl3/hexane = 1/2 v/v) of 6 (the precursor of 1) gave rise to well-separated fractions from which enantiomers of 6 (Figure 2a)

were isolated. The circular dichroism (CD) spectra of theenantiomers were complete mirror images (Figure 2b);hereafter, each enantiomer of 6 is expressed as 6CD(+) or6CD(−) based on the sign of the CD signal at 300 nm. As in thecase of racemic 6, reduction of optically active 6, for example,6CD(+), with HSiCl3 gave optically active 1CD(+), which displayedclear CD peaks (Figure S1).

Pd-Catalyzed Suzuki−Miyaura Cross-Coupling UsingRacemic 1. With racemic 1, we examined the catalytic activityof the triptycene-based monophosphine ligand for Pd-catalyzedSuzuki−Miyaura cross-coupling (Table 1). As a typicalexample, when p-bromotoluene (7a, 1.0 mmol) was reactedwith phenylboronic acid (8a, 1.25 mmol) in 2-methoxyethanolfor 2 h at 60 °C under aerobic conditions in the presence of 1.0mol % Pd(OAc)2, 2.0 mol % 1, and K3PO4 (2.0 mmol), 4-methyldiphenyl (9a) was isolated in 99% yield (entry 1, Table1). We investigated the effects of the solvent (Table S1), base(Table S3), and Pd source (Table S2) on the cross-coupling of

Figure 1. (a) Perspective and (b) top view of triptycene and itsnumbering. (c) Structures of chiral 1,8,13-substituted triptycenes and(d) their geometrical models.

Scheme 1. Synthesis of 1a

aReagents and conditions: (a) Tf2O, pyridine, 1,2-dichloroethane, 60°C, 75%; (b) diphenylphosphine oxide, Pd(OAc)2, 1,4-bis-(diphenylphosphino)butane, diisopropylethylamine, DMSO, 100 °C,90%; (c) NaOH, 1,4-dioxane, MeOH, 25 °C, 94%; (d) MeI, K2CO3,acetone, 25 °C, 95%; and (e) HSiCl3, triethylamine, toluene, 120 °C,90%.

Figure 2. (a) Chiral HPLC traces of racemic 6, 6CD(−) and 6CD(+)(CHIRAL ART Amylose-SA column, YMC CO., LTD.; diameter: 4.6mm; length: 250 mm; eluent: CHCl3/hexane = 1/2, v/v; flow rate: 0.5mL/min; detection: UV absorption at 250 nm). (b) CD and UVspectra of 6CD(−) (50 μM) and 6CD(+) (50 μM) in CH2Cl2 at 25 °C.

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7a and 8a with 1.0 mol % PdCl2, 2.0 mol % 1, and K3PO4 (2.0mmol). The cross-coupling reaction in 2-methoxyethanol or amixture of tetrahydrofuran (THF)/H2O (1/1 in vol) led to thehighest yield of 9a (99%, entries 4 and 13, Table S1), whereasthat in methanol or isopropyl alcohol resulted in 9a in less than10% yield. Among the various bases examined, the use ofK3PO4, in combination with 2-methoxyethanol, gave the bestresult (entry 1, Table S3). For the Pd(II) source, PdCl2 andPd(OAc)2 allowed the quantitative conversion of 7a and 8ainto 9a (entries 1 and 4, Table S2), whereas the use ofPdCl2(PPh3)2 or Pd2(dibenzylideneacetone)3 under identicalconditions lowered the yield of 9a (entries 2 and 3, Table S2).Based on the above experimental results, we set 2-methoxyethanol, K3PO4, and Pd(OAc)2 as the standardcombination for Pd-catalyzed Suzuki−Miyaura cross-couplingwith 1.Remarkably, the use of only 0.001 mol % (i.e., 10 mol ppm)

Pd(OAc)2 and 1 (2 equiv for Pd) could achieve the quantitativeformation of 9a from 7a and 8a (entry 2, Table 1), whichindicates that the turnover number (TON) of the catalyticsystem is as high as 99 000. An even higher TON (108 000)was obtained when the cross-coupling was performed with a 5mol ppm Pd loading, though the yield of 9a decreased to 54%(entry 3, Table 1). In sharp contrast, when the cross-couplingreaction was conducted using Pd(OAc)2 alone (10 mol ppm ofPd loading), 9a was obtained in only 15% yield (entry 4, Table1). In the presence of PPh3 (2 equiv for Pd), the yield of 9a wasincreased to some extent (35%; entry 5, Table 1). When asterically bulky phosphine ligand such as (2-biphenylyl)-diphenylphosphine was used (2 equiv for Pd) in place ofPPh3, the yield of 9a was greatly improved (70%; entry 6, Table1), yet it was lower than that achieved in the cross-couplingreaction with Pd(OAc)2/1. Therefore, we consider that asynergetic effect, arising from the steric bulkiness around thephosphine group and the rigidity of the triptycene scaffold,would lead to the excellent catalytic activity of 1.10

Substrate Scope of Pd(OAc)2/1 Catalyst for Suzuki−Miyaura Cross-Coupling. Table 2 shows the substrate scopeof the catalytic system of Pd(OAc)2/1 for the Suzuki−Miyauracross-coupling of various aryl bromides (7b−7j, 1.0 mmol) andphenylboronic acid (8a, 1.25 mmol) with Pd(OAc)2 (10 molppm), 1 (20 mol ppm), and K3PO4 (2.0 mmol) in 2-

methoxyethanol under aerobic conditions. Biaryl products 9b−9e were formed quantitatively (99% yield) from aryl bromides7b−7e with an electron-withdrawing substituent such as NO2,CF3, COMe, or CHO (entries 1−4). On the other hand, theefficiency of the cross-coupling between 8a and aryl bromides7f−7h containing an electron-donating substituent (NH2, p-OMe, m-OMe, or o-OMe) was slightly decreased, giving rise tobiaryls 9f−9h in 80−85% yield (entries 5−7). Notably, when 7iand 7j bearing relatively sterically demanding o-OMe and o-CH3 substituents, respectively, were subjected to Pd(OAc)2/1-catalyzed cross-coupling, the corresponding products wereobtained in good yields (9i: 85% and 9j: 93%, entries 8 and 9).Meanwhile, the cross-coupling of p-chlorotoluene with 8a didnot proceed under the reaction conditions, resulting incomplete recovery of the starting materials.

Table 1. Pd(OAc)2/1-Catalyzed Suzuki−Miyaura Cross-Coupling of p-Bromotoluene 7a with Phenylboronic Acid 8a underVarious Reaction Conditionsa

entry Pd (mol ppm)b 1 (mol ppm)b temperature (°C) time (h) yield (%)c TON TOF (h−1)

1 10 000 20 000 60 2 99 99 502 10 20 100 24 99 99 000 41253 5 10 100 24 54 108 000 45004d 10 0 100 24 15 15 000 6255e 10 0 100 24 35 35 000 14586f 10 0 100 24 70 70 000 2917

aReaction conditions: 1 (2 equiv for Pd), 4-bromotoluene (1.0 mmol), phenylboronic acid (1.25 mmol), K3PO4 (2.0 mmol), 2-methoxyethanol (6mL), 100 °C, 24 h. b1 mol ppm equals 0.0001 mol %. cIsolated yield. dIn the absence of 1. eIn the presence of 20 mol ppm PPh3.

fIn the presence of20 mol ppm (2-biphenylyl)diphenylphosphine.

Table 2. Scope of Aryl Bromides 7b−7j for Pd/1-CatalyzedSuzuki−Miyaura Cross-Coupling with Phenylboronic Acid8aa

entry R1 product yield (%)b

1 p-NO2 (7b) 9b 992 p-CF3 (7c) 9c 993 p-COMe (7d) 9d 994 p-CHO (7e) 9e 995c m-NH2 (7f) 9f 806 p-OMe (7g) 9g 857 m-OMe (7h) 9h 808c o-OMe (7i) 9i 859 o-Me (7j) 9j 93

aReaction conditions: Pd(OAc)2 (10 mol ppm), 1 (20 mol ppm), arylbromide (1.0 mmol), phenylboronic acid (1.25 mmol), K3PO4 (2.0mmol), 2-methoxyethanol (6 mL), 100 °C, 24 h. bIsolated yield.cPd(OAc)2 (50 mol ppm) and 1 (100 mol ppm).

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As summarized in Table 3, we further examined Pd(OAc)2/1-catalyzed Suzuki−Miyaura cross-coupling using aryl bromides

(7b, 7d, and 7g) and substituted phenylboronic acids (8b−8d).Under conditions identical to those described in Table 2, thecross-coupling of electron-deficient aryl bromides (7b and 7d)with 8b bearing an electron-withdrawing CF3 group gave thecorresponding biaryls in high yields (86−99%, entries 1 and 2).A similar result was obtained when electron-rich arylboronicacid 8c was used in place of 8b (entries 3 and 4). Asrepresented by entries 5 and 6, the catalytic system ofPd(OAc)2/1 worked very efficiently for cross-coupling evenwith sterically demanding o-methylphenylboronic acid (8d).Meanwhile, for electron-rich aryl bromides such as 7g, toachieve a satisfactory yield of biaryl products, the reactionshould be conducted with a larger amount of the Pd source, forexample, 50 mol ppm of Pd(OAc)2 (entry 7) or in the presenceof tetra-n-butylammonium bromide (entries 8 and 9), which isa promising additive for improving Pd-catalyzed reactions.14

Single-Crystal X-ray Structural Analysis of a PdComplex with Racemic 1. To gain insight into the structureof the catalytic species, we attempted to crystallize a Pd/1complex directly from a mixture of Pd(OAc)2 and racemic 1.Although this attempt was not successful, a dark orange-coloredblock-shaped single crystal suitable for X-ray crystallographywas obtained when a 1:1 mixture of Pd(OAc)2 and 1 wastreated with NaBr and recrystallized from a mixture of CH2Cl2and diethyl ether (see the Supporting Information).15 The X-ray diffraction analysis of the single crystal revealed theformation of a dimer of PdBr2/1 (10), where Pd atoms arebridged by μ-Br atoms (Figure 3). The dimer formation is incontrast to the case of a previously reported mononuclearPdCl2 complex of chiral 1-p-tolylthio-8-(diphenylphosphino)-triptycene,9 where the PdCl2(II) is simply ligated with the Patom of the triptycene and a THF molecule without formingsuch a dimeric structure. In the crystal structure of 10, the

phosphorous atoms of 1 bind to Pd with interatomic Pd−Pdistances of 2.2493(12) and 2.2456(12) Å (Figure 3).16

Notably, although 1 exists as a racemic mixture in the unitcell (space group = P21/c, Z = 4), each molecule of PdBr2/1 iscomposed of homochiral 1. This structural feature suggests that1 could provide a chiral environment around the coordinationsphere of Pd for asymmetric organic transformations.For reference, we tested the Suzuki−Miyaura cross-coupling

of 7a and 8a using complex 10 (10 mol ppm) as a catalystunder otherwise identical conditions to those in Table 1. Asshown in Scheme S1, the coupling reaction took place veryefficiently to give 9a in 95% yield. Given that the 1:1 complexof PdBr2 and 1 (10) exhibits an excellent catalytic activity, a 1:1complex of other Pd source and 1 would be the active speciesin the catalytic system for the Suzuki−Miyaura cross-coupling.

Pd-Catalyzed Asymmetric Reactions Using OpticallyActive 1CD(+). Because of the limited variation in the chiralMOP ligands in comparison with the large variation inbidentate phosphine ligands, 1 seemed to be promising as anew candidate for the chiral MOP ligand. First, we conductedthe Suzuki−Miyaura cross-coupling of 1-bromo-2-methylnaph-thalene (7k) or 1-bromo-2-methoxynaphthalene (7l) with 2-methylphenylboronic acid (8d) in the presence of opticallyactive 1CD(+) (Scheme 2).17 Although these reactions showedhigh or moderate yields (9t: 86% and 9u: 63%), noenantiomeric excesses (ee) of these products were observed(Figures S2 and S3).Next, we conducted a Pd-catalyzed hydrosilylation reac-

tion11,18 by using 1CD(+) as a chiral ligand (Scheme 3). Styrenewas reacted with HSiCl3 in the presence of [PdCl(π-allyl)]2(0.25 mol %) and 1CD(+) (0.60 mol %) in toluene at 25 °C togive 11 in 52% isolated yield. The Tamao oxidation of 11 usingH2O2, KF, and KHCO3 afforded an optically active 1-phenylethanol (12), whose ee value was determined to be58% with R configuration (Figure S4). Although theenantioselectivity was moderate in this reaction, this result

Table 3. Scope of Arylboronic Acids 8b−8d for Pd/1-Catalyzed Suzuki−Miyaura Cross-Coupling with ArylBromides 7b, 7d, and 7ga

entry R1 R2 product yield (%)b

1 p-NO2 (7b) p-CF3 (8b) 9k 992 p-COMe (7d) p-CF3 (8b) 9l 863 p-NO2 (7b) m,p-(OMe)2 (8c) 9m 994 p-COMe (7d) m,p-(OMe)2 (8c) 9n 905 p-NO2 (7b) o-Me (8d) 9o 996c p-COMe (7d) o-Me (8d) 9p 997c p-OMe (7g) p-CF3 (8b) 9q 998c,d p-OMe (7g) m,p-(OMe)2 (8c) 9r 979c,d p-OMe (7g) o-Me (8d) 9s 86

aReaction conditions: Pd(OAc)2 (10 mol ppm), 1 (20 mol ppm), arylbromide (1.0 mmol), arylboronic acid (1.25 mmol), K3PO4 (2.0mmol), 2-methoxyethanol (6 mL), 100 °C, 24 h. bIsolated yield. cInthe presence of n-Bu4NBr (2.0 mmol).

dPd(OAc)2 (50 mol ppm) and1 (100 mol ppm).

Figure 3. Molecular structure of dimeric complex 10 (50% probabilityellipsoids). Hydrogen atoms and solvent molecules are omitted forclarity. Selected bond distances (Å) and angles (deg): P(2)−O(2) =4.495(4), P(1)−O(1) = 4.424(4), P(2)−Pd(2) = 2.2493(12), P(1)−Pd(1) = 2.2456(12), Pd(1)−O(1) = 3.446(4), Pd(2)−O(2) =4.580(4), P(2)−Pd(2)−Br(3) = 93.6(4), and P(1)−Pd(1)−Br(3) =93.6(4).

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clearly indicated that 1CD(+) could serve as a chiral mono-phosphine ligand.

■ CONCLUSIONSIn conclusion, inspired by a geometrical model (Figure 1d), wedesigned a triptycene-based monophosphine ligand, 1-me-thoxy-8-(diphenylphosphino)triptycene (1), for the develop-ment of a new catalytic system for transition metal-catalyzedorganic transformation. Surprisingly, there has been noprevious report on the catalytic application of a triptycene ofthis type. Compound 1 was obtained in a manner similar to thesynthesis of well-known MOP.11,12 Using Pd-catalyzed Suzuki−Miyaura cross-coupling, we demonstrated the catalytic activityof 1 complexed with Pd(II). The catalytic system workedefficiently for cross-coupling reactions between a wide variety ofaryl bromides and arylboronic acids and gave the correspondingbiaryls in good to excellent yields (80−99%), even when the Pdloading was as low as 0.001 mol %. The successful chiral HPLCseparation of the precursor of 1 allowed the synthesis ofoptically active 1. Although this chiral ligand was unable toinduce chirality in Suzuki−Miyaura cross-coupling, it wasapplicable to a Pd-catalyzed asymmetric hydrosilylationreaction. The ee of the product was moderate (58% ee), butthis was surprising considering the rather simple stereo-chemistry of 1, which may be described as a triangle withthree dif ferent poles at the apexes (Figure 1d). These resultsshow the potential of this triptycene-based monophosphineligand with structural rigidity and steric bulkiness around thephosphine group. Thus, proper modifications of this prototype,in terms of the triptycene skeleton itself and substituents of

phosphine and alkoxy groups, might lead to new highly efficientcatalytic systems to give a particular stereoselectivity.

■ EXPERIMENTAL SECTIONMaterials. Unless otherwise noted, all commercial reagents

were purchased from commercial suppliers (Sigma-Aldrich andTokyo Chemical Industry) and used without purifications.Anhydrous CH2Cl2 and toluene were dried by passing themthrough an activated alumina column and a Q-5 column (NikkoHansen). 1,8-Dihydroxytriptycene13 was prepared according topreviously reported procedures and unambiguously charac-terized by nuclear magnetic resonance (NMR) spectroscopyand APCI-TOF mass spectrometry.

General. Column chromatography was carried out usingWakogel silica C-300 (particle size: 45−75 μm). Recyclingpreparative chiral HPLC was carried out on an LC-9210 NEXTrecycling preparative HPLC system (Japan Analytical Industry),equipped with CHIRAL ART Amylose-SA column, YMC Co.,Ltd. (diameter: 20 mm; length: 250 mm) and a multi-wavelength detector (MD-2010Plus). Analytical chiral HPLCwas carried out on a JASCO HSS-1500 system, equipped withCHIRAL ART Amylose-SA column, YMC Co., Ltd. (diameter:4.6 mm; length: 250 mm) or CHIRALCEL OD-H column,DAICEL Co., Ltd. (diameter: 4.6 mm; length: 250 mm).Melting points (mp) and decomposition points (dp) wererecorded on a Yanaco MP-500D melting-point apparatus. IRspectra were recorded at 25 °C on a JASCO FT/IR-660PlusFourier transform IR spectrometer. CD spectra were recordedon a JASCO J-820 spectropolarimeter. NMR spectroscopymeasurements were taken at 25 °C on a Bruker AVANCE IIIHD500 spectrometer (1H: 500.0 MHz, 13C: 125.0 MHz, 19F:470.5 MHz, and 31P: 202.0 MHz) or on a Bruker AVANCE-400 spectrometer (1H: 400.0 MHz and 13C: 100.0 MHz) or ona Varian 400-MR (1H: 400.0 MHz and 13C: 100.0 MHz).Chemical shifts (δ) are expressed relative to the resonances ofthe residual nondeuterated solvent for 1H (CDCl3:

1H (δ) =7.26 ppm and DMSO-d6:

1H (δ) = 2.50 ppm), 13C (CDCl3:13C (δ) = 78.0 ppm and DMSO-d6:

13C (δ) = 39.5 ppm),external CF3CO2H in CDCl3 for

19F (19F (δ) = −78.5 ppm),and external H3PO4 in CDCl3 for 31P (31P (δ) = 0.0 ppm).Absolute values of the coupling constants are given in hertz,regardless of their sign. Multiplicities are abbreviated as singlet(s), doublet (d), triplet (t), quartet (q), and multiplet (m).APCI-TOF mass spectrometry measurements were taken on aBruker micrOTOF II mass spectrometer equipped with anatmospheric pressure chemical ionization (APCI) or electro-spray ionization (ESI) probe. Specific optical rotations ofoptically active compounds were measured on a JASCO P-2200digital polarimeter in a 5 cm quartz cuvette at 25 °C.

1,8-Bis-(trifluoromethanesulfonyloxy)triptycene (3). At 25°C, triflic anhydride (3.0 mL, 18 mmol) was added to a 1,2-dichloroethane solution (50 mL) of a mixture of 1,8-dihydroxytriptycene 2 (1.30 g, 4.55 mmol) and pyridine(3.00 mL, 37.3 mmol). The resultant mixture was stirred at 60°C for 18 h, allowed to cool to 25 °C, poured into water (100mL), and extracted with CHCl3 (100 mL, three times). Theorganic extract was washed successively with water and brine,dried over anhydrous MgSO4, and evaporated to dryness underreduced pressure. The residue was subjected to columnchromatography on SiO2 (hexane/CHCl3; v/v = 3/1) toallow the isolation of 3 as a white powder (1.88 g, 3.42 mmol)in 75% yield: mp: 191 °C. FT-IR (KBr) v (cm−1): 3078, 1613,1579, 1465, 1429, 1251, 1212, 1135, 1098, 996, 958, 892, 862,

Scheme 2. Asymmetric Suzuki−Miyaura Cross-CouplingUsing Optically Active 1CD(+)

a,b

aIsolated yield. bThe ee values were determined by HPLC(CHIRALCEL OD-H with n-hexane, see the Supporting Information).

Scheme 3. Asymmetric Hydrosilylation Reaction UsingOptically Active 1CD(+)

a,b

aIsolated yield. bThe ee value was determined by HPLC(CHIRALCEL OD-H with n-hexane/2-PrOH = 95/5, see theSupporting Information).18

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821, 792, 752, 733, 712, 666, 648, 629, 608, 571, 517, 499. 1HNMR (500 MHz, CDCl3): δ (ppm) 7.50−7.49 (m, 1H), 7.43−7.41 (m, 3H), 7.11−7.07 (m, 4H), 6.98 (d, J = 10.5 Hz, 2H),6.15 (s, 1H), 5.58 (s, 1H). 13C NMR (125 MHz, CDCl3): δ(ppm) 148.7, 144.3, 144.1, 141.6, 136.0, 127.5, 126.2, 126.1,125.2, 124.0, 123.7, 122.5, 120.0, 118.8, 117.4, 114.9, 53.7, 42.4.19F NMR (470 MHz, CDCl3): δ (ppm) −73.2. High-resolutionACPI-TOF mass: calcd for C22H12O6F6S2 [M]+: m/z =549.9974; found, 549.9953. 1H and 13C NMR spectra of 3are shown in Figures S7 and S8, respectively.8-Trifluoromethanesulfonyltriptycene-1-diphenylphos-

phine Oxide (4). Under argon at 25 °C, N,N-diisopropylethyl-amine (0.63 mL, 3.6 mmol) was added to a DMSO solution(4.0 mL) of a mixture of 3 (0.50 g, 0.91 mmol),diphenylphosphine oxide (0.38 g, 1.88 mmol), Pd(OAc)2(10.2 mg, 0.045 mmol), and 1,4-bis(diphenylphosphino)butane(19.4 mg, 0.045 mmol). The resultant mixture was stirred at100 °C for 12 h, allowed to cool to 25 °C, poured into water(100 mL), and extracted with ethyl acetate (100 mL, threetimes). The organic extract was washed successively with waterand brine, dried over anhydrous MgSO4, and evaporated todryness under reduced pressure. The residue was subjected tocolumn chromatography on SiO2 (ethyl acetate/CH2Cl2; v/v =9/1) to allow the isolation of a racemic mixture of 4 as a whitepowder (0.49 g, 0.81 mmol) in 90% yield: mp: 206 °C. FT-IR(KBr) v (cm−1): 3419, 3073, 2959, 2932, 2834, 2345, 2216,1941, 1701, 1613, 1580, 1480, 1465, 1428, 1322, 1206, 1135,1098, 1067, 996, 958, 892, 862, 822, 791, 752, 722, 708, 696,679, 666, 647, 629, 608, 570, 543, 517, 499, 458. 1H NMR (500MHz, CDCl3): δ (ppm) 7.71−7.67 (dd, J = 7.5, 4.5 Hz, 4H),7.56−7.54 (m, 3H), 7.47−7.44 (m, 4H), 7.34−7.32 (dd, J =7.5, 2.5 Hz, 2H), 7.02−6.95 (m, 3H), 6.86−6.85 (m, 3H), 6.57(d, J = 7.5 Hz, 1H), 6.52 (s, 1H), 5.51 (s, 1H). 13C NMR (125MHz, CDCl3): δ (ppm) 149.1, 148.3, 148.2, 146.9, 146.8,144.8, 144.3, 142.0, 136.3, 133.1, 132.7, 132.3, 132.2, 132.1,132.0, 131.9, 131.8, 131.7, 129.4, 129.3, 129.2, 128.8, 128.7,128.6, 128.5, 128.4, 127.5, 127.4, 126.9, 125.6, 125.5, 125.2,125.1, 125.0, 123.4, 123.3, 119.9, 118.7, 117.3, 54.0, 46.0. 19FNMR (470 MHz, CDCl3): δ (ppm) −73.3. 31P NMR (202MHz, CDCl3): δ (ppm) 29.2. High-resolution ACPI-TOFmass: calcd for C33H22O4F3PS [M]+: m/z = 602.0934; found:602.0922. 1H and 13C NMR spectra of 4 are shown in FiguresS9 and S10, respectively.8-Hydroxytriptycene-1-diphenylphosphine Oxide (5). An

aqueous solution (10 mL) of NaOH (1.20 g, 30 mmol) wasdropwise added to a MeOH/1,4-dioxane solution (18 mL; v/v= 1/2) of 4 (0.40 g, 0.77 mmol), and the mixture was stirred at25 °C for 12 h. After the addition of an aqueous solution ofHCl (1 N, 20 mL) to the reaction mixture, a white precipitateformed was collected by filtration, washed with water (100mL), and dried under reduced pressure. The residue wassubjected to column chromatography on SiO2 (CH2Cl2) toallow the isolation of a racemic mixture of 5 as a white powder(0.34 g, 0.72 mmol) in 94% yield: mp: 313 °C. FT-IR (KBr) v(cm−1): 3071, 1592, 1474, 1455, 1437, 1418, 1238, 1169, 1142,1116, 930, 832, 790, 725, 706, 644, 611, 565, 542, 454. 1HNMR (500 MHz, CDCl3): δ (ppm) 8.87 (s, 1H), 7.78 (dd, J =7.5, 4.5 Hz, 1H), 7.67−7.65 (m, 3H), 7.64−7.49 (m, 6H), 7.40(d, J = 8.0 Hz, 1H), 7.00 (dd, J = 7.5, 7.5 Hz, 1H), 6.95 (d, J =7.0 Hz, 1H), 6.87−6.83 (m, 3H), 6.70 (d, J = 7.5 Hz, 1H), 6.41(dd, J = 7.5, 4.5 Hz, 1H), 6.41 (s, 1H), 6.39 (d, J = 7.5 Hz, 1H),5.45 (s, 1H). 13C NMR (125 MHz, CDCl3): δ (ppm) 152.5,150.9, 150.8, 148.3, 148.2, 146.6, 144.7, 142.6, 132.5, 132.5,

132.4, 132.3, 132.2, 132.1, 132.0, 130.9, 129.1, 128.9, 128.7,128.6, 127.9, 127.8, 127.7, 127.6, 126.3, 125.7, 124.3, 124.2,124.1, 123.5, 116.2, 116.1, 54.0, 46.2, 46.1. 31P NMR (202MHz, CDCl3): δ (ppm) 32.9. High-resolution ACPI-TOFmass: calcd for C32H23O2P [M]+: m/z = 470.1430; found:470.1428. 1H and 13C NMR spectra of 5 are shown in FiguresS11 and S12, respectively.

8-Methoxytriptycene-1-diphenylphosphine Oxide (6).Methyl iodide (0.1 mL, 1.2 mmol) was added to an acetonesolution (20 mL) of 5 (0.20 g, 0.43 mmol) and K2CO3 (0.24 g,1.2 mmol) and stirred at 25 °C for 3 h. The reaction mixturewas poured into water (100 mL) and extracted with ethylacetate (100 mL, three times). The organic extract was washedsuccessively with water and brine, dried over anhydrousMgSO4, and evaporated to dryness under reduced pressure.The residue was subjected to column chromatography on SiO2(CH2Cl2) to allow the isolation of 6 as a white powder (0.20 g,0.41 mmol) in 95% yield: mp: 224 °C. FT-IR (KBr) v (cm−1):3402, 3057, 3019, 2958, 2932, 2834, 2215, 1904, 1826, 1707,1590, 1481, 1458, 1436, 1415, 1323, 1267, 1190, 1159, 1145,1118, 1097, 1071, 1026, 997, 967, 927, 874, 831, 786, 752, 722,705, 696, 647, 608, 591, 566, 544, 475. 1H NMR (500 MHz,CDCl3): δ (ppm) 7.65−7.57 (m, 4H), 7.51 (dd, J = 7.5, 3.0 Hz,3H), 7.42−7.37 (m, 4H), 7.29 (d, J = 7.0 Hz, 1H), 6.98 (d, J =7.0 Hz, 1H), 6.95−6.82 (m, 6H), 6.56 (s, 1H), 6.41 (d, J = 8.0Hz, 1H), 5.43 (s, 1H), 3.41 (s, 3H). 13C NMR (125 MHz,CDCl3): δ (ppm) 154.7, 150.2, 150.1, 147.8, 147.7, 147.5,145.5, 144.2, 134.0, 133.1, 133.0, 132.4, 132.3, 132.2, 132.1,131.8, 131.7, 131.6, 131.4, 129.2, 129.1, 128.5, 128.4, 128.3,128.2, 127.5, 127.4, 127.3, 126.7, 126.3, 125.2, 124.9, 124.7,124.5, 124.4, 123.3, 116.0, 109.4, 108.0, 81.2, 55.3, 54.4, 44.8,24.9. 31P NMR (202 MHz, CDCl3): δ (ppm) 30.1. High-resolution ACPI-TOF mass: calcd for C33H25O2P [M + H]+:m/z = 485.1665; found: 485.1651. 1H and 13C NMR spectra of6 are shown in Figures S13 and S14, respectively. Opticallyactive 6CD(+) and 6CD(−), which were obtained by the opticalresolution using chiral HPLC (CHIRAL ART Amylose-SAcolumn, CHCl3/hexane = 1/2 v/v), showed specific opticalrotations ([α]D

25) of 24.8 and −25.0, respectively, in CHCl3 (c =0.04 g/dL).

8-Methoxytriptycene-1-diphenylphosphine (1). Underargon at 25 °C, HSiCl3 (0.16 mL, 1.6 mmol) was addeddropwise to a toluene solution (15 mL) of a mixture of 6 (0.15g, 0.31 mmol) and triethylamine (0.87 mL, 6.2 mmol), and theresultant mixture was stirred at 120 °C for 18 h and allowed tocool to 25 °C. An aqueous solution (50 mL) of NaHCO3 (4.2g, 50 mmol) was added slowly to the reaction mixture andextracted with diethyl ether (100 mL, three times). The organicextract was washed successively with water and brine, driedover anhydrous MgSO4, and evaporated to dryness underreduced pressure. The residue was subjected to columnchromatography on SiO2 (hexane/CH2Cl2; v/v = 3/1) toenable the isolation of 1 as a white powder (0.13 g, 0.28 mmol)in 90% yield: mp: 216 °C. FT-IR (KBr) v (cm−1): 3446, 3051,3001, 2952, 2928, 1589, 1480, 1457, 1432, 1416, 1324, 1267,1193, 1160, 1097, 1071, 1025, 964, 909, 786, 767, 746, 729,694, 679, 646, 591, 539, 500, 466. 1H NMR (500 MHz,CDCl3): δ (ppm) 7.35−7.20 (m, 12H), 7.00 (dd, J = 7.0, 7.0Hz, 2H), 6.94−6.85 (m, 4H), 6.49−6.41 (m, 3H), 5.41 (s, 1H),5.28 (s, 1H), 3.51 (s, 3H). 13C NMR (125 MHz, CDCl3): δ(ppm) 154.7, 149.9, 149.6, 147.7, 146.0, 145.8, 144.6, 136.7,136.6, 134.3, 134.1, 134.0, 133.9, 132.3, 131.8, 131.7, 128.9,128.6, 128.5, 128.4, 128.3, 128.2, 125.0, 124.9, 124.3, 124.1,

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123.3, 116.1, 108.2, 55.5, 54.5, 44.6, 44.5. 31P NMR (202 MHz,CDCl3): δ (ppm) −14.7. High-resolution ACPI-TOF mass:calcd for C33H25OP [M + H]+: m/z = 469.1716; found:469.1728. 1H and 13C NMR spectra of 1 are shown in FiguresS5 and S6, respectively. Optically active 1CD(+) that wasprepared from 6CD(+) showed a specific optical rotation ([α]D

25)of 77.9 in CHCl3 (c = 0.04 g/dL).[PdBr2-1]2 (10). At 25 °C, NaBr (100 mg, 0.97 mmol) was

added to a 2-methoxyethanol solution (4 mL) of a mixture ofracemic 1 (22 mg, 0.047 mmol) and Pd(OAc)2 (10.6 mg, 0.047mmol), and the mixture was stirred at 25 °C for 1 h and thenpoured into water (10 mL). The resultant brown precipitatewas collected by filtration, washed with water (20 mL), anddried under reduced pressure. The residue was recrystallizedfrom CH2Cl2 under diethyl ether vapor to give [PdBr2-1]2 10as dark orange single crystals (68 mg, 0.0465 mmol) in 99%yield: mp: 252 °C. FT-IR (KBr) v (cm−1): 3447, 3056, 2956,2931, 2832, 2356, 1590, 1481, 1457, 1435, 1416, 1314, 1267,1187, 1159, 1141, 1094, 1074, 998, 966, 924, 871, 828, 786,750, 730, 691, 646, 607, 591, 543, 514, 475. 1H NMR (500MHz, DMSO-d6): δ (ppm) 7.82 (dd, J = 8.0, 4.0 Hz, 2H), 7.64(d, J = 7.0 Hz, 1H), 7.59−7.58 (m, 1H), 7.51−7.47 (m, 3H),7.41 (d, J = 7.0 Hz, 3H), 7.20−7.09 (m, 5H), 7.04−6.89 (m,4H), 6.77 (dd, J = 10.0, 10.0 Hz, 1H), 6.58 (d, J = 8.0 Hz, 1H),5.74 (s, 1H), 3.32 (s, 3H). 13C NMR (125 MHz, DMSO-d6): δ(ppm) 154.8, 148.9, 148.8, 147.8, 147.6, 147.5, 146.2, 144.5,137.4, 137.3, 134.9, 134.8, 132.2, 131.5, 131.0, 128.7, 128.6,128.2, 127.8, 127.6, 127.2, 126.9, 125.7, 125.2, 124.9, 123.8,116.3, 108.5, 55.1, 53.5, 45.9, 45.8. 31P NMR (202 MHz,DMSO-d6): δ (ppm) 25.5. High-resolution ESI-TOF mass:calcd for C66H50Pd2O2P2Br4 [M − Br]+: m/z = 1388.8901;found: 1388.8916. 1H and 13C NMR spectra of 10 are shown inFigures S15 and S16, respectively.General Experimental Procedures for Pd/1-Catalyzed

Suzuki−Miyaura Cross-Coupling. A 2-methoxyethanolsolution (6 mL) of a mixture of aryl bromides 7 (1.0 mmol),arylboronic acid 8 (1.25 mmol), Pd(OAc)2 (0.001 mol %, 10mol ppm), 1 (0.002 mol %, 20 mol ppm), and K3PO4 (2.0mmol) was added to a reaction tube. The reaction mixture wasstirred at 100 °C for 24 h under air, allowed to cool to 25 °C,poured into water (25 mL), and extracted with ethyl acetate(30 mL, three times). The organic extract was washedsuccessively with water and brine, dried over anhydrousMgSO4, and evaporated to dryness under reduced pressure.The residue was subjected to column chromatography, whichenabled the isolation of the desired product 9.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acsomega.7b00200.

Tables S1−S3, Scheme S1, and Figures S1−S60 (PDF)Crystallographic data for 10 (CIF)

■ AUTHOR INFORMATIONCorresponding Authors*E-mail: ymayamada@riken.jp (Y.M.A.Y.).*E-mail: fukushima@res.titech.ac.jp (T.F.).ORCIDYoshiaki Shoji: 0000-0001-8437-1965Yuuya Nagata: 0000-0001-5926-5845Michinori Suginome: 0000-0003-3023-2219

Takanori Fukushima: 0000-0001-5586-9238NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work was partially supported by a Grant-in-Aid forScientific Research on Innovative Areas “π-Figuration” (no.26102008 for T.F., no. 15H00994 for Y.N.) and “DynamicAlliance for Open Innovation Bridging Human, Environmentand Materials” from the Ministry of Education, Culture, Sports,Science and Technology of Japan (MEXT). F.K.C.L. kindlyacknowledges the International Program Associate (IPA) ofRIKEN. We thank K. Osakada and D. Takeuchi (TokyoInstitute of Technology) for their support with the specificoptical rotation measurement. We thank Suzukakedai MaterialsAnalysis Division, Technical Department, Tokyo Institute ofTechnology, for their support with the NMR measurement.

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ACS Omega Article

DOI: 10.1021/acsomega.7b00200ACS Omega 2017, 2, 1930−1937

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