Diastereoselective ortholithiation and conformational control in stereospecific dearomatising anionic cyclisations

Abstract

The dearomatising anionic cyclisation of tertiary naphthamides bearing chiral N-substituents (such as α-methylbenzyl) is stereospecific and retentive not because of a configurationally stable organolithium intermediate but because the starting material exists as two atropisomers at −78°C, of which only one is lithiated. The initially formed ortholithiated amide can be trapped with MeI to give single diastereoisomers of atropisomeric amides bearing chiral N-substituents. Given time, even in the absence of DMPU, the ortholithiated amide undergoes anion translocation to an α-lithiated species, which can cyclise only to one diastereoisomer of the product, leading to the observed stereospecificity.