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.