Rhodium-catalyzed formal (3 + 3) transannulation of 1,2,3-thiadiazoles with vinyloxiranes

Abstract

A rhodium-catalyzed formal (3 + 3) transannulation of 1,2,3-thiadiazoles and vinyloxiranes is realized, accessing 2,3-dihydrothiopyran-4-ones in moderate to good yields. The transannulation is a tandem sequence of the Lewis-acid–catalyzed Meinwald rearrangement of vinyloxiranes and formal (3 + 3) transannulation of formed alk-2-enals and in situ–generated 1-thia-2-rhodacyclobutenes from 1,2,3-thiadiazoles, rather than a thioacyl-carbene–induced ring expansion of oxiranes, different from the reaction of acylcarbenes with oxiranes and thiiranes.