Synthesis of Dihydropyrans and Dihydrofurans via Radical Cyclization of Unsaturated Alcohols and 1,3-Dicarbonyl Compounds.

The oxidative cyclization reactions of 1,3-dicarbonyl compounds 1a- 1c and α, β-unsaturated alcohols 2a- 2f with Mn(OAc)3 were performed, leading to dihydrofurans. Treatment of 1a and 1b with 2-methylbut-3-en-2-ol ( 2a) gave dihydrofurans 3aa and 3ba, and dihydropyrans 4aa and 4ba, as unexpected products. While the reaction of 2-methylbut-3-yn-2-ol ( 2b) with acetylacetone ( 1b) yielded a bifuran, ethyl acetoacetate ( 1a) led to a mixture of furan, bifuran, and salicylate derivatives. Besides, surprisingly, styryl-substituted dihydrofurans were obtained from the reactions of 1,3-dicarbonyl compounds and (3 E)-2,4-diphenylbut-3-en-2-ol. The reaction mechanisms were proposed for the formation of the different products, considering intermediates in these reaction mixtures. [ABSTRACT FROM AUTHOR]