Gold(III) Chloride-Catalyzed Diastereoselective Alkylation Reactions with Chiral Benzylic Acetates
作者:Philipp Rubenbauer、Thorsten Bach
DOI:10.1002/adsc.200700600
日期:2008.5.5
Gold(III) chloride was shown to be an efficient catalyst for the diastereoselective CC bond formation of various chiral para-methoxybenzylic acetates and different nucleophiles. All electrophilic acetates carried next to the reacting center a stereogenic carbon center bound to a functional group (FG), a methyl substituent and a proton. Selectivities were good (dr>80/20) in favor of the anti-product
氯化金(III)被证明是形成各种手性对甲氧基苄基乙酸酯和不同亲核试剂的非对映选择性CC键的有效催化剂。所有亲电子的乙酸酯在反应中心附近均带有与官能团(FG),甲基取代基和质子键合的立体碳中心。选择性好(dr > 80/20),对于FG = COOMe,NO 2和CN有利于产生反产物,对于FG = SO 2 Et,PO(OEt)2有利于合成产物。反应最有可能通过一种游离碳正离子,其中优选的构象可促进面部分化。几种芳烃亲核试剂显示与催化条件兼容,可提供高收率的相应取代产物(13个实例,占62-98%)。此外,其他亲核试剂(烯丙基三甲基硅烷,三甲基甲硅烷基氰化物,2,2-二甲基-3-(三甲基甲硅烷基氧基)丁烷,对甲苯磺酰胺和乙酰丙酮)与代表性手性亲电子试剂以高产率和非对映选择性的方式反应。
High Facial Diastereoselectivity in Intra- and Intermolecular Reactions of Chiral Benzylic Cations
attacked by arene nucleophiles with high facial diastereoselectivity (dr >/= 94/6). Benzylic cations, such as 2, were generated under acidic conditions and reacted with arenes in intra- and intermolecular Friedel-Crafts alkylation reaction. The depicted reaction 1 --> 3 represents one example for the unprecedented, highly diastereoselectiveintermolecular Friedel-Crafts alkylation reactions which were
Chiral α-Branched Benzylic Carbocations: Diastereoselective Intermolecular Reactions with Arene Nucleophiles and NMR Spectroscopic Studies
作者:Friedrich Mühlthau、Daniel Stadler、Alain Goeppert、George A. Olah、G. K. Surya Prakash、Thorsten Bach
DOI:10.1021/ja062102g
日期:2006.8.1
significant racemization was observed (94% ee --> 92% ee). The reactions proceed stereoconvergently as demonstrated by the conversion of the separated diastereoisomers syn-1a and anti-1a in separate reactions to the same product syn-11 (d.r. = 97/3). Further evidence for long-lived chiral benzylic carbocations as reaction intermediates was obtained from NMR studies in superacidic medium. The chiral cation