Morita-Baylis-Hillman-Type [3,3]-Rearrangement: Switching from Z- to E-Selective alpha-Arylation by New Rearrangement Partners

摘要

alpha-aryl alpha,beta-unsaturated carbonyls represent an important class of derivatizable synthetic intermediates, however, the synthesis of such compounds still remains a challenge. Recently, we showcased a novel Z-selective alpha-arylation of alpha,beta-unsaturated nitriles with aryl sulfoxides via [3,3]-rearrangement involving an Morita-Baylis-Hillman (MBH) process. Herein, we demonstrate the feasibility of reversing the stereoselectivity of such MBH-type [3,3]-rearrangement by switching to a new pair of rearrangement partners consisting of aryl iodanes and alpha,beta-unsaturated oxazolines. As a result, the two protocols complement each other in approaching E- or Z-alpha-aryl alpha,beta-unsaturated carbonyl derivatives. Mechanistic studies reveal a possible reaction pathway and provide an explanation for the opposite stereoselectivities.