Diastereoselective conjugate addition of thiols to camphor pyrazolidinone derived chiral α,β-unsaturated carbonyls: synthesis of β-mercaptocarboxylic acid derivatives

Reaction of chiral α,β-unsaturated carboxylic acid derivatives 2a–e derived from camphor pyrazolidinone 1 with thiols affords β-mercaptocarboxylic acid derivatives 3a–e with a wide range of stereoselectivities (up to >90% de). The stereoselectivity as a function of Lewis acid is described. The auxiliary can be easily recovered from the Michael adducts under mild conditions.