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Synthesis and chemistry of endoperoxides derived from 3,4-dihydroazulen-1(2H)-one: An entry to cyclopentane-anellated tropone derivatives

2000-01-01
Celik, M
Akbulut, N
Balcı, Metin
Reduction of trienone 1 and subsequent treatment with acid in MeOH furnished 1-methoxy-1,2,3,4-tetrahydroazulene (13). Photo-oxygenation of 13 provided the two bicyclic endoperoxides 14 and 15. Pyrolysis of 14 and 15 gave the corresponding bis-epoxides 17 and 18, which have been synthesized also upon treatment with a catalytic amount of CoTPP (TPP = tetraphenylporphyrin). That an unusual endoperoxide-endoperoxide rearrangement has not been observed strongly supports the assumption that the carbonyl group in 2-4 is responsible for this unprecedented endoperoxide-endoperoxide rearrangement. Treatment of the endoperoxides 14 and 15 with a catalytic amount of Et3N at 0 degrees provided the azulenones 22 and 23 in high yield. Attempted cleavage of the O-O peroxide linkage in 14 and 15 with thiourea resulted, contrary to our expectation, in the formation of 22 and 23. That thiourea acts as a base instead of a reducing reagent has been observed for the first time in peroxide chemistry.