Carbon−Carbon Bond-Forming Reaction of Cyclic Sulfonium Ylides Stabilized by a Carbonyl Group

Rhodium(II)-catalyzed decomposition of diazoketones 1 and 5 bearing a cyclic dithioacetal, in the presence of aldehyde and ClTi(Oi-Pr)3, afforded both or one of the CC-bonded products, i.e., ring-enlarged enone 2 and ring-transformed thiophenone 3, that were formed between aldehyde and intermediate bicyclosulfonium ylide. The stereochemistry of the exocyclic CC bond in the products was exclusively Z. The sulfonium atom that transiently composed the ylide was incorporated into products, but no oxirane was formed.