Fragmentation of bicyclic γ-silyloxy-β-hydroxy-α-diazolactones as an approach to ynolides

Medium-sized ynolides were prepared by the Lewis acid-mediated fragmentation of bicyclic γ-silyloxy-β-hydroxy-α-diazolactones in which the Cβ-Cγ bond is the ring fusion bond. Although these lactone fragmentation substrates reacted somewhat less efficiently than their carbocyclic counterparts, the fragmentation provided 11-membered ynolides in up to 84% yield. Unlike prior fragmentations of similar substrates, elevated temperatures were required to obtain optimum yields of the ynolide products. The ynolides reported herein have ring sizes of 10 or 11, which are the smallest reported to date.