有機合成化学協会誌
Online ISSN : 1883-6526
Print ISSN : 0037-9980
ISSN-L : 0037-9980
総説および総合論文
塩基を必要としない中性相間移動反応系の発見と展開
白川 誠司
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2014 年 72 巻 12 号 p. 1374-1383

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Although quaternary onium salts-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles to nitroolefins proceeded smoothly in the presence of lipophilic quaternary ammonium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate addition and aldol reactions under the influence of chiral bifunctional ammonium bromides as key catalysts. The efficient approach for the design of chiral quaternary phosphonium bromides as chiral phase-transfer catalysts was also introduced. A catalyst library with various structures has readily been constructed by the use of commercially available chiral phosphines as catalyst precursors. The optimized catalyst has successfully been applied to highly enantioselective conjugate additions and sulfenylation under base-free neutral phase-transfer conditions with low catalyst loading.

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