A stereodivergent synthesis of β-hydroxy-α-methylene lactonesviavinyl epoxides

Abstract

A catalytic diastereoselective sulfonium ylide epoxidation of aldehydes furnished original vinyl epoxides, having an MBH backbone. These highly functionalised building blocks were used for a formal synthesis of the antibiotic conocandin, and opened up a stereodivergent route towards β-hydroxy-α-methylene lactones, core units of naturally occurring compounds. Under acidic conditions, the oxiranes were mainly transformed, with moderate to good yields, into transβ-hydroxy-α-methylene lactones. On the other hand, a user-friendly palladium-catalysed CO₂insertion and cyclisation sequence gave the cisβ-hydroxy-α-methylene lactone counterparts along with an interesting cis–trans equilibration of the π-allyl intermediates.