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Paper | Regular issue | Vol 65, No. 10, 2005, pp.2411-2430
Published online, 12th August, 2005
DOI: 10.3987/COM-05-10498
Synthesis and Unambiguous Stereochemical Determination of 1-exo- and 1-endo-1-Aryl-1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones

Masayuki Yamashita, Yadav Navnath Dnyanoba, Masaki Nagahama, Tomoki Inaba, Yuka Nishino, Kumiko Miura, Sachiko Kosaka, Junko Fukao, Ikuo Kawasaki, and Shunsaku Ohta*

*Kyoto Pharmaceutical University, Misasagi, Yamashina-ku, Kyoto 607-8412, Japan

Abstract

Stereoselective preparation of 1-exo-substituted 1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones (2) was achieved by photo [2+2] cycloaddition of olefins to 3-substituted coumarins (1). 1-endo-Substituted 1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones (3) were stereoselectively prepared by hydrogenation over the Pd-carbon of 2a,8b-dihydro-3H-benzo[b]cyclobuta[d]pyran-3-ones (5), which were obtained by photo [2+2] cycloaddition of the coumarins (1) to acetylenes. The stereochemistry of 1-exo- and 1-endo-arylcyclobutanes (2 and 3) could be easily determined on the basis of the 1H-NMR spectrum, in which the C8-proton in 3 was strongly shielded by the 1-aryl ring but that in 2 was not.