Stereoselective addition of lithium amides to activated triple bonds

Abstract

The nucleophilic addition of R″₂NLi to alkyl esters of R′CCCO₂R (R′= H, CO₂R; R = Me, Et) in apolar solvents, in the presence and in the absence of solvating agents, has been studied. The only or the main reaction product obtained under all experimental conditions was the corresponding (E)-R″₂NCR′CHCO₂R. It is suggested that the vinyl-lithium intermediate, which is first formed by an anti-type addition of R″₂NLi to the triple bond, undergoes a very fast isomerisation, owing to the highly effective configurationally destabilising R⁺ effect of the electron-donating dialkylamino trans-β-substituent.