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Communication | Regular issue | Vol 12, No. 5, 1979, pp.641-645
Published online, 1st January, 1970
DOI: 10.3987/R-1979-05-0641
Primary and Secondary Photochemistry of α-Tropolone Methyl Ether

O. L. Chapman,* M. A. Hems, J. D. Lassila, and C. Kreil

*Department of Chemistry, University of California, One Shields Avenue, Davis, CA 95616-5295, U.S.A.

Abstract

The photoisomerization of α-tropolone methyl ether to 1-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one proceeds via the S1 state. Irradiation of 1-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one gives 6-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one and 7-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one. The 6-methoxy product is formed via α-cleavage in the T1 state. The 7-methoxy product is formed in a process involving a deep-seated skeletal rearrangement. The first step in this rearrangement involves formation of cis,cis-2-methoxybicyclo[2.1.0]pent-2-en-5-yl ketene from the S1 state of 1-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one. The ketene intermediate is converted to 7-methoxybicylo[3.2.0]hepta-3,6-dien-2-one by a facile Cope rearrangement which proceeds rapidly above 233K.