Synthesis, applications and mechanistic investigations of C2 symmetric guanidinium salts
Synthesis, applications and mechanistic investigations of C2 symmetric guanidinium salts
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DOI：
10.1016/j.tet.2015.11.058
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发表时间：
2016-01-28
期刊：
影响因子：
2.1
通讯作者：
O'Donoghue, AnnMarie C.
中科院分区：
文献类型：
--
作者：
Allingham, Matthew T.;Bennett, Elliot L.;O'Donoghue, AnnMarie C.
用六步或七步合成了一系列的胍催化剂，并用于21-86%ee中甘氨酸Schiff碱的相转移烷基化反应和85-94%ee中查尔酮的相转移环氧化反应。用分光光度法测定了一些催化剂在DMSO中的pK(A)值在13.2-13.9范围内，突出了相对于去手性四甲基胍(pK(A)=13，0)的碱度增加，并提出了质子化的胍离子作为相转移催化剂的机理。考察了其中两种催化剂在Michael加成反应中的应用，发现两种催化剂都是有效的催化剂。在这些反应中有明显的反离子效应，但没有观察到对映体选择性。(C)2015爱思唯尔有限公司。保留所有权利。
A range of guanidinium catalysts was prepared in six or seven synthetic steps and applied to the phase transfer alkylation of a glycinate Schiffs base in 21-86% ee as well as the phase transfer epoxidation of some chalcones in 85-94% ee. Using a spectrophotometric method, pK(a) values in the range 13.2-13.9 in DMSO have been determined for some of the catalysts highlighting an increase in basicity relative to achiral tetramethylguanidine (pK(a)=13,0) and a mechanism involving the protonated guanidinium ion as a phase transfer catalyst is proposed. The use of two of the catalysts for the addition of nucleophiles in Michael addition reactions was investigated and both were found to be effective catalysts. A counterion effect was apparent in these reactions, but no enantioselectivity was observed. (C) 2015 Elsevier Ltd. All rights reserved.