The 2‐thienyl‐substituted 4,5‐dihydrofuran derivatives 3–8 were obtained by the radicalcyclizationreaction of 1,3‐dicarbonyl compounds 1a–1f with 2‐thienyl‐substituted conjugated alkenes 2a–2e by using [Mn(OAc)3] (Tables 1–5). In this study, reactions of 1,3‐dicarbonyl compounds 1a–1e with alkenes 2a–2c gave 4,5‐dihydrofuran derivatives 3–5 in high yields (Tables 1–3). Also the cyclic alkenes 2d