Thermal and Photochemical Reactions of Some Bicyclic Aziridine Enol Ethers

Acid-base-catalyzed, thermal, and photochemical rearrangements of some bicyclic aziridine enol ethers are described. For example, 6-phenyl-2,4-bis(benzhydrylidene)-3,5-dioxa-l-azabicyclo[4.1.0]heptane (3a), an azirine-ketene adduct, rearranges on alumina to give dioxazepine 4, which undergoes a further transformation to yield lactone 6. The latter is converted to the isomeric 1,3 diketone 8 on treatment with alcoholic base. On the other hand, thermolysis of 3a at 140-150° gives the seven-membered ring diether 15a, an isomer of 4, and lactone 16a, an isomer of 6. Dioxazepine 15a rearranges to 16a on further heating while 15c leads to the five-membered lactone 19c. Photolysis of 3a at 310 nm results in the formation of a mixture of compounds from which 15a and 16a are isolated. Further photolysis of 15a affords 16a. These results are discussed. The mechanistic pathway for both pyrolysis and photolysis involves R-O cleavage of a cyclic enol ether C=C-O-R followed by O-C or C-C ring closurewith rearrangement of R.