Asymmetric deprotonations: Lithiation of N-(tert-butoxycarbonyl)indoline with sec-butyllithium/(-)-sparteine

The asymmetric lithiation of N-Boc indoline (1) with s-BuLi/(-)-sparteine and subsequent substitution provides the 2-substituted N-Boc indolines 3 and 5-11 with excellent enantiomeric ratios and in variable yields. The asymmetric lithiation-substitution sequence with N-Boc-7-chloroindoline (12) provides products 13-19 with good enantiomeric ratios. Mechanistic investigation establishes that the enantioselectivities arise from an initial asymmetric deprotonation to provide the enantioenriched and configurationally stable organolithium intermediates (S)-28 and (S)-29, which react stereoselectively with electrophiles.