β-Shielded Michael systems whose H–C(sp2) deprotonation and 1,2-addition reactions compete for organolithiums
作者:Rudolf Knorr、Barbara Schmidt、Johannes Freudenreich、Therese von Roman
DOI:10.1016/j.tet.2018.11.020
日期:2018.12
Steric shielding of an α,β-unsaturated nitrile R2C = CH–CN by tert-alkyl β-substituents (R) prevented 1,4-additions of organolithiums and showed a remarkably solvent-dependent selectivity of tert-butyllithium (tBuLi): 1,2-addition at CN and α-deprotonation occurred almost equally fast in THF, while CN addition was exclusive in Et2O. The resultant N-lithioimine was cleanly α-deprotonated (albeit with
叔烷基β-取代基(R)对α,β-不饱和腈R 2 C = CH–C N的立体屏蔽可防止有机锂的1,4-加成,并显示出叔丁基锂(tBuLi)对溶剂的选择性显着):在C N处1,2加成和α-去质子化在THF中几乎一样快,而在Et 2 O中C N加成是排他的。所得的N-硫代亚胺在原位被干净地α-去质子化(尽管有异常缓慢)。超出tBuLi的数量。亚胺被水解生成烯酮,R 2 C = CH–C(R')= O,具有庞大的取代基R和R',允许添加C O,但不被异丁基锂进行α-去质子化,正丁基锂(nBuLi),甚至是非常坚固的碱tBuLi。-2,4,6-三-叔-butylphenyllithium(“*的Mes李”)没有添加或质子化烯酮。然而,使用N-硫代-2,2,6,6-四甲基哌啶(LTMP)作为催化剂,Mes * Li在已知的Mes *自由基重排和随后的羰基添加同时实现了α-去质子化。以KOH或KOtBu为基础的[D