Studies on the Radical Cyclization of 3-Oxopropanenitriles and Alkenes with Cerium(IV) Ammonium Nitrate in Ether Solvents

The radical cyclization of 3-oxopropanenitriles 1a-1e and alkenes 2a-2g with cerium(IV) ammonium nitrate (CAN) in ether solvents was investigated (Tables I and 2). In the optimization study, 1,3-dioxolane, 1,4-dioxane, 1,2-dimethoxyethane, Et2O, and THF were used as ether-based solvents, and the latter was found to be the most effective solvent in radical cyclizations mediated by cerium(IV). This system (cerium(IV)/THF) was applied to cyclizations of various 3-oxopropanenitriles and 1,3-dicarbonyl compounds with alkenes resulting in the formation of 4,5-dihydrofurans in high yields (Table 2 and Scheme 2). The results of the cerium(IV)/THF radical cyclization were compared with those obtained with manganese(III) acetate/AcOH; the cerium(IV)/THF system turned out to be much more efficient.