Ring transformation of 1,5-diazabicyclo[3.1.0]hexanes under the action of arylketenes

The reactions of 1,5-diazabicyclo[3.1.0]hexanes 8 with arylketenes 1 have been studied in different conditions. The 1-(arylacethyl)pyrazolidines 11 were obtained at −30 °C in ether and at 20 °C in benzene instead of the expected bicyclic systems 1,5-diazabicyclo[3.2.1]octan-6-one 9 and 3-aryl-1,5-diazabicyclo[3.3.0]octane-2-one 10. The synthesis of two representatives of bicycles 10 (10a,b) proceeded in the reaction of unsubstituted 1,5-diazabicycle[3.1.0]hexane 8a, accordingly, with diphenylketene 1a in benzene at 20 °C and with 4-chlorophenylketene 1b in toluene at 60-110 °C. Mechanisms of the studied transformations were offered.