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Lewis Base/Brønsted Acid Co-catalyzed Asymmetric Thiolation of Alkenes with Acid-Controlled Divergent Regioselectivity.

A divergent strategy for the facile preparation of various enantioenriched phenylthio-substituted lactones was developed based on Lewis base/Brønsted acid co-catalyzed thiolation of homoallylic acids. The acid-controlled regiodivergent cyclization (6-endo vs 5-exo) and acid-mediated stereoselective rearrangement of phenylthio-substituted lactones were explored. Experimental and computational studies were performed to clarify the origins of the regioselectivity and enantioselectivity. The calculation results suggest that C-O and C-S bond formation might occur simultaneously, without formation of a commonly supposed catalyst-coordianted thiiranium ion intermediate and the potential π-π stacking between substrate and SPh as an important factor in the enantiodetermining step. Finally, this methodology was applied in the rapid syntheses of bioactive natural products (+)-ricciocarpin A and (R)-dodecan-4-olide.