Guanidine-catalyzed asymmetric synthesis of 2,2-disubstituted chromane skeletons by intramolecular oxa-Michael addition
Guanidine-catalyzed asymmetric synthesis of 2,2-disubstituted chromane skeletons by intramolecular oxa-Michael addition
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DOI：
10.1002/ejoc.200800089
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发表时间：
2008-06-01
影响因子：
2.8
通讯作者：
Ishikawa, Tsutomu
中科院分区：
文献类型：
--
作者：
Saito, Noriko;Ryoda, Akemi;Ishikawa, Tsutomu
已经检查了在 C-5 碳上具有 2-羟基芳基部分的 α,β-不饱和酯在胍催化的 6-exo-trig 型分子内不对称 oxa-Michael 加成反应中是否构建了具有季碳手性中心的苯并二氢吡喃骨架。烷基的体积和a,p-不饱和酯官能团的E/Z几何结构在不对称诱导中发挥着重要作用，并且在4-和5-位带有芳基侧链的(4S,5S)-2-[(R)-1-羟甲基-2-苯基乙基亚氨基]-1,3-二甲基咪唑烷（或其对映体）被发现是所检查的18种手性胍中最有效的催化剂。通过这种方式，体积较小的甲酯的 Z 异构体进行环化反应，得到手性苯并二氢吡喃，产率高达 83%，ee 为 76%。 （(c) Wiley-VCH Verlag GmbH & Co. KGaA，69451 Weinheim，德国，2008 年）。
The guanidine-catalyzed 6-exo-trig-type intramolecular asymmetric oxa-Michael addition of alpha,beta-unsaturated esters with a 2-hydroxyaryl moiety at the C-5 carbon has been examined for the construction of chromane skeletons with a quaternary carbon chiral center. The bulkiness of the alkyl group and the E/Z geometry of the a,p-unsaturated ester function played important roles in the asymmetric induction and (4S,5S)-2-[(R)-1-hydroxymethyl-2-phenylethylimino]-1,3-dimethylimidazolidine (or its enantiomer) carrying aryl pendants at the 4- and 5-positions was found to be the most effective catalyst among 18 chiral guanidines examined. In this way, the Z isomer of the less bulky methyl ester was subjected to the cyclization reaction, affording chiral chromane in up to 83 % yield with 76 % ee. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).