Rearrangement of isoxazoline-5-spiro derivatives. Part 7. Thermal rearrangement of 4,5-dihydro and tetrahydroisoxazole-5-spirocyclobutanes to azepin-4-one derivatives

Article abstract of DOI:10.1016/S0040-4020(01)89026-8

Some representative 4,5-dihydro and tetrahydroisoxazole-5-spirocyclobutanes have been synthesized by 1,3-dipolar cycloaddition of alkylidenecyclobutanes to nitrile oxides and nitrones, respectively. When subjected to flash vacuum thermolysis conditions, the spiranic cycloadducts rearranged to afford mainly the desired azepin-4-one derivatives. In addition, the isoxazoline cycloadducts gave unexpected by-products, which were identified as 1-alkenyl-2-pyrrolidinones. Analogies and differences with respect to the lower homologue cyclopropanes are evidenced in both cycloaddition and rearrangement reactions.