Functionalized oxepines via fragmentation of highly strained epoxides.

[Structure: see text] Epoxidation of highly strained cyclobutenes followed by thermal rearrangement provides a new entry into oxepine-containing bicyclo[5.3.0] ring systems. In contrast to the rearrangement of the corresponding cyclopropanated systems, the strained epoxides in this study are believed to fragment through two competing pathways leading to a mixture of diastereomeric 5-7 ring systems.