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

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