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Intramolecular Photocyclization of 2-Acylphenyl Methacrylates: a Convenient Access to 4,5-Dihydro-1,4-epoxy-2-benzoxepin-3(1H)-ones (= Benzo[c]-6,8-dioxabicyclo[3.2.1]octan-7-ones

✍ Scribed by Takehiko Nishio; Nobuharu Sakurai; Kaoru Iba; Yo-ichi Hamano; Masami Sakamoto

Publisher
John Wiley and Sons
Year
2005
Tongue
German
Weight
106 KB
Volume
88
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The photochemical reactions of 2‐acylphenyl methacrylates (= 2‐acylphenyl 2‐methylprop‐2‐enoates) 1 were investigated. Irradiation of 2‐acylphenyl methacrylates 1a–d in MeCN gave the tricyclic lactones 2a–d in good yields, together with a small amount of OCO bond cleavage product, the 2‐acylphenols 3a–d (Scheme 2, Table). The formation of the tricyclic lactones 2 probably follows a mechanism involving a 1,7‐diradical through ζ‐H abstraction (1,8‐H transfer) by the excited carbonyl O‐atom (Scheme 3). Irradiation of 2‐acylphenyl tiglate (= 2‐acylphenyl (2__E__)‐2‐methylbut‐2‐enoate) 1e and 2‐acylphenyl methacrylates 1g–i, substituted by a MeO group (δ‐H) at the 3,5‐positions of the phenyl group, also gave the tricyclic lactones 2e and 2g–i, but in low yields. On the other hand, no H‐abstraction products were observed on irridation of 2‐(ethoxycarbonyl)phenyl methacrylate 1f, of 2‐acylphenyl methacrylate 1j which is substituted by a Me group (γ‐H) at the 3,5‐positions of the phenyl group, and of 1k with an OH group at the 3‐position of the phenyl group.

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