Novel photorearrangement of a 4-chloromethylazulene

1-Chloro-4,6,8-trimethylazulene is formed almost exclusively upon UV irradi ation of a deaereted benzene solution of 4-chloromethyl-6.8-dimethylazulene . This photoproduct was identified by H-1 and C-13 NMR spectroscopy of both the isolated photoproduct and the one prepared by a thermal route. The mec hanism proposed involves the recombination of the intimate radical pair ini tially formed by the photohomolysis of the C-Cl bond, followed by a sigmatr opic [1.9] hydrogen shift. (C) 2001 Published by Elsevier Science Ltd.