Radical Cyclization of Fluorinated 1,3-Dicarbonyl Compounds with Dienes Using Manganese(III) Acetate and Synthesis of Fluoroacylated 4,5-Dihydrofurans

Radical cyclizations of fluorinated 1,3-dicarbonyl compounds with dienes mediated by Mn(OAc)3 afforded 4,5-dihydrofurans containing difluoroacetyl, trifluoroacetyl, or heptafluorobutanoyl groups in good-to-excellent yields. Additionally, 2-(difluoromethyl)-4,5-dihydrofurans and a 4,7-dihydrooxepin derivative were obtained as unexpected products in the reaction of 4,4-difluoro-1-phenylbutane-1,3-dione with 1,3-diphenylbuta-1,3-diene. The radical cyclization of symmetrical dienes such as 2,3-dimethylbuta-1,3-diene and 1,4-diphenylbuta-1,3-diene with 1,3-diketones furnished the corresponding products in low yields. However, treatment of 1-phenylbuta-1,3-diene with 1,3-dicarbonyl compounds afforded 4,5-dihydrofurans containing fluoroacyl groups. The radical cyclizations with 3-methyl-1-phenylbuta-1,3-diene and 1,3-diphenylbuta-1,3-diene led to 4,5-dihydrofurans in good yields, since Me and Ph groups at C(3) of these dienes increase the stability of the radical intermediate.