First Enantioselective Synthesis of Gingesulfonic Acids and Unequivocal Determination of their Absolute Stereochemistry.

Herein we report the first organocatalysed enantioselective synthesis of gingesulfonic acids and shogasulfonic acids via a mild and convenient aminothiourea-catalysed conjugate addition of bisulfite to the olefin moiety of α,β-unsaturated carbonyls a technology previously reported by us. A series of optically active naturally occurring sulfonic acids are prepared in their natural and unnatural configurations, and their absolute configurations are unequivocally confirmed by single crystal X-ray diffractometry.