Diastereodivergent Synthesis of Benzylic Quaternary Centers Mediated by a Remote Sulfinyl Group: Spectroscopic Evidence of the Structure of the Carbanionic Intermediates

Abstract

Enantiomerically enriched α,α-disubstituted phenyl acetonitriles were prepared from 2-alkyl-2-[2-(p-tolylsulfinyl)phenyl]acetonitriles by reaction with alkylating and acylating reagents under basic conditions. NMR spectroscopic studies corroborated the structure of the intervening carbanions, the nature of which was closely dependent on the employed base. Michael additions and tandem sequences involving Michael and aldol reactions were successfully developed for the simultaneous creation of up to four stereocenters. The newly synthesized compounds bearing suitably substituted quaternary benzylic carbons were used as substrates for a highly stereoselective sulfinyl-mediated Pauson–Khand cycloaddition.

Keywords:

• Asymmetric synthesis
• carbanions
• diastereoselectivity
• NMR spectroscopy
• sulfoxide