A New Protocol for the Consecutive alpha-and beta-Activation of Propiolates towards Electrophiles,Involving Conjugate Addition of Tertiary Amines and Intramolecular Silyl Migration

摘要

Herein,we present a novel approach for the consecutive a-and[3-activation of conjugated alkynes and demonstrate the application of this methodology towards the C-C bond-forming reactions of propiolates.This new concept is based on the 1,4-addi-tion of a tertiary amine to a conjugated alkyne,followed by an aldol-type addition to an aldehyde and subsequent intramolecular silyl migration.This sequential process is generally applicable for 3-trimethylsilylpropiolates.The combination of methyl 3-trimethylsilyl-propiolate, 1,4-diazobicyclo-[2.2.2]octane(DABCO),and aromatic aldehydes brought about domino-type C-C bond formations to afford highly functionalized olefins as the major products.On the other hand,aliphatic aldehydes,including the sterically demanding aromatic aldehyde,2,6-dime-thylbenzaldehyde,produced alkyne derivatives as the sole products from the reaction,presumably,by the reaction pathway common to the first cases.The intramolecular version of the reaction was successfully applied to the cycliza-tion of trimethylsilylpropiolic esters derived from salicylaldehydes,leading to a new formylcoumarin synthesis.Studies of the reaction mechanisms are also described.