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An Opinion Poll on Long Distance Race Running among Primary School Students

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この文字を消してTitleを入れてください HETEROCYCLES, Vol. 87, No. 6, 2013, pp. 1319 - 1326. © 2013 The Japan Institute of Heterocyclic Chemistry Received, 25th March, 2013, Accepted, 25th April, 2013, Published online, 30th April, 2013 DOI: 10.3987/COM-13-12718 INTRAMOLECULAR [2+2]-PHOTOCYCLIZATION AND CONFORMATIONAL PREFERENCE OF 5-(2-BENZO[b]THIENYL)-5- ETHOXY-5H-DIBENZO[a,d]CYCLOHEPTENE Motoko Akita, Sin-ya Mohri, Mai Takahashi, and Keiji Kobayashi* Department of Chemistry, Graduate School of Material Science, Josai University, Keyakidai, Sakado, Saitama 350-0295, Japan; E-mail: [email protected] Abstract – The photoirradiation of 5-(2-benzo[b]thienyl)-5-ethoxy-5H-dibenzo- [a,d]cycloheptene (2) in acetonitrile afforded a cagelike tetracyclic compound (1) via intramolecular [2+2]-photocycloaddition. The molecular and crystal structures of 1 and 2 were characterized by a single-crystal X-ray diffraction study. The formation of the cycloadduct is discussed in relation to the preferable conformation of the central C-C bond in 2, which was revealed to be in restricted rotation on the basis of the temperature-dependent 1 H NMR spectra. Thiophene derivatives show versatile photoreactivity and wide mechanistic perspectives. 1 An unsaturated bond of the thiophene ring frequently exhibits photoreactivity as a 2-electron component. A relevant example is the photoinduced electrocyclization of 1,2-di(2-thienyl)ethylenes to give a cyclohexadiene framework, which has been attracting considerable attention in relation to photochromic functions. 2 The thiophene ring of benzo[b]thiophenes also participates in inter- and intramolecular [2+2]-cycloadditions.3 We previously reported the novel intramolecular photocyclization and di--methane rearrangement of tris(2-benzo[b]thienyl)methane derivatives.4,5 In the course of our continuous study, we have now found an unexpected intramolecular [2+2]-photocyclization of 5-(2-benz

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