Enantioselective ring opening of meso-epoxides with tetrachlorosilane catalyzed by chiral bipyridine N,N′-dioxide derivatives

Nakajima, Makoto; Saitô, Makoto; Uemura, M.; Hashimoto, Shunichi

doi:10.1016/s0040-4039(02)02229-3

Cited by 107 publications

(42 citation statements)

References 21 publications

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“…Catalyst 14 provided better ee values than 15 for acyclic epoxides (Table 1, entries 1-3), but the opposite was true for the cyclic epoxide (Table 1, entry 4). Overall, 16 was found to be better in terms of enantioselectivity than 14 and 15, and is comparable to the best catalysts in the literature [14] for both aromatic-and alkyl-substituted epoxides. The scope of the present reaction was additionally probed with catalyst, 16 ( Table 2).…”

Section: Norito Takenaka* Robindro Singh Sarangthem and Burjor Captainsupporting

confidence: 58%

“…[14] All three compounds (P)-14-16 were found to sufficiently catalyze the ring-opening reaction of cis-stilbene oxide by SiCl 4 and provided the corresponding (R,R)-chlorohydrin with high ee values (Table 1, entry 1). For the three catalsyts, the ring opening proceeded in better enantioselectivity for substrates having aromatic substituents rather than for those bearing alkyl groups (Table 1, entries 1 and 2 versus 3 and 4).…”

Section: Norito Takenaka* Robindro Singh Sarangthem and Burjor Captainmentioning

confidence: 99%

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Helical Chiral Pyridine N‐Oxides: A New Family of Asymmetric Catalysts

2008

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The design, synthesis, and study of new catalyst structures have had an enormous impact on chemical synthesis, and continue to be a central challenge in asymmetric catalysis.[1]We recently described that a 2-aminopyridinium ion might be a promising catalaphore [2] for the design of new asymmetric hydrogen-bond donor catalysts. [3] In that connection, we became interested in 1-aza [6]helicene [4] 1 as a chiraphore [2] because a first-order analysis of the crystal structure of an analogous 1,16-diaza[6]helicene [5] suggests that its pyridine ring is well-desymmetrized in terms of both top-from-bottom and left-from-right differentiations. To our knowledge, the application of 1 and analogous helical chiral pyridines [5][6][7] in asymmetric catalysis has not been studied, even though 1 has been known in the literature since 1975.[4d] In this context, we were prompted to develop an efficient synthesis of 1-azahelicenes, which allows systematic structural variation-important for the elucidation of the relationship between catalyst structure, reactivity, and selectivity-and to exploit them as chiraphores. In view of the utility of helical chiral pyridines such as 1, it occurred to us that the corresponding pyridine N-oxides might prove to be effective asymmetric catalysts.[8] Herein, we describe the scalable synthesis of 1-azahelicenes and the structural characterization of the corresponding N-oxides, and we apply this new family of compounds to the catalytic enantioselective desymmetrization of meso epoxides (see Table 1). This study provides the first report of the application of azahelicenes in asymmetric catalysis. [9] An examination of the structure of 1 suggests that the chiral environment in the vicinity of the nitrogen atom can be tuned by structural modification at cabon atoms 11-16. Therefore, we devised a convergent synthetic route to 1 in which benzoquinoline unit 2 and C11-C16 unit 3 could be expeditiously united (Scheme 1). This strategy would allow ready access to the necessary 1-azahelicene derivatives by simply replacing 3 with its readily available structural analogues, such as 9 and 12 (Scheme 2). Preparation of key unit 8 starts from commercially available pyridine 4 and phosphonium salt 5, which was readily synthesized in three steps from commercially available 2-bromo-4-methyl benzaldehyde. The highly Z-selective Wittig reaction [6b, 10] of 4 and 5 and subsequent Stille-Kelly reaction [5,11] provided benzoquinoline 6. The catalytic C À H functionalization method developed by Sanford and co-workers [12] readily converted 6 into 7 from which 8 was obtained in an ordinary way. The second sequence of the highly Z-selective Wittig reaction and the Stille-Kelly reaction of 8 with 9, 11, or 12 provided 1-azahelicenes 10, 1, or 13, respectively. The scalability of this Scheme 1. Synthesis design.Scheme 2. Syntheses of 1-azahelicenes: a) NaHMDS, DMF, 78 %; b) [PdCl 2 (Ph 3 P) 2 ], (Me 3 Sn-) 2 , PhMe, 77 %; c) Pd(II) catalyst, [12] NBS, CH 3 CN, 84 %; d) benzoyl peroxide, NBS, PhH, 71 %; e) 2-nitropropane,...

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Section: Norito Takenaka* Robindro Singh Sarangthem and Burjor Captainsupporting

confidence: 58%

Section: Norito Takenaka* Robindro Singh Sarangthem and Burjor Captainmentioning

confidence: 99%

Helical Chiral Pyridine N‐Oxides: A New Family of Asymmetric Catalysts

2008

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“…[34] The use of the chiral phosphoramide (R)-1 in combination with SiCl 4 led to the enantioselective synthesis of chlorohydrins, Scheme 12. Following our initial report, other groups described the use of N-oxides, [35,36] phosphines, [37] and phosphine oxides [38] (Scheme 13). As part of an ongoing program in these laboratories on Lewis base-catalyzed reactions of silicon tetrachloride, we sought to investigate a number of preparative and mechanistic features of the epoxide ring opening reaction to garner a clearer understanding of the role of each of the reaction components and potentially the origin of enantioselectivity.…”

Section: Introductionmentioning

confidence: 99%

Enantioselective Ring Opening of Epoxides with Silicon Tetrachloride in the Presence of a Chiral Lewis Base: Mechanism Studies

et al. 2007

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Abstract:The enantioselective ring opening of mesoepoxides (from both cyclic and acyclic olefins) with silicon tetrachloride under catalysis by chiral phosphoramides affords enantiomerically enriched chlorohydrins in excellent yields. Experiments designed to elucidate the mechanistic foundation and origins of enantioselectivity are described. From studies on the loading and stoichiometry of the reagent (SiCl 4 ) and the catalyst [(R)-1] it was established that only one chloride per SiCl 4 is delivered and that the nature of reactive species does not change over the course of the reaction. Kinetic studies together with asymmetric amplification experiments have suggested that more than one catalyst molecule may be bound to SiCl 4 in the stereochemistry-determining transition structure.

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“…[1,2] A number of valuable products could be synthesized when reagents such as trialkylsilyl azide, [3][4][5][6] trimethylsilyl cyanide, [7][8][9][10] aryllithium, [11] halides [12][13][14] and alkylamines, [15] alcohols/phenols, [16,17] thiols, [18,19] as well as carboxylic acid [20] were used as nucleophiles for ring-opening reactions of epoxides. A catalytic asymmetric ring opening of meso-epoxide with aromatic amines is of particular interest because it has wider applications in the synthesis of pharmaceutically active compounds.…”

Section: Introductionmentioning

confidence: 99%