Concerted and stepwise Grignard additions, probed with a chiral Grignard reagent
Abstract
The Grignard reagent 6, in which the magnesium-bearing carbon atom is the sole stereogenic centre has been added to CO2, PhNCO, PhNCS and certain aldehydes with full retention of configuration. Reaction with benzophenone, electron-deficient aldehydes and several allyl halides proceeded with partial or complete racemization. The findings are discussed with respect to a dichotomy between concerted polar and stepwise SET reaction pathways.