Stable Iso-osmabenzenes from a Formal 3+3 Cycloaddition Reaction of Metal Vinylidene with Alkynols

摘要

The investigation on the synthesis and reactivity of metal vinylidene complexes has always been an active area, especially given their applications as well-known catalysts for metathesis and carbon-carbon and carbon-heteroatom coupling reactions. Compared with other reactions of metal vinylidenes, the cyclization reactions are underdevel- oped. Previous studies showed that the vinylidene M=C_α bond participated in cyclo-additions (see a) as key steps in carbon-carbon coupling reactions, and some cycloaddition products have also been isolated. Interestingly, similar reactions of the metal vinylidene C_α=C_β bond (see b) have been realized as well. However, cyclizations of the skeleton of metal vinylidene (M=C_α=C_β) as a unit (see c) remain scarce. In fact, the reported cyclization is a formal 3+2 cycloaddition reac-tion. To the best of our knowledge, the 3+3 cyclization reactions of metal vinylidene to construct six-membered rings have not been reported.