Functionalized fluoroalkyl heterocycles by 1,3-dipolar cycloadditions with γ-fluoro-α-nitroalkenes

Differently fluorinated gamma-fluoro-alpha-nitroalkenes 1a-d are effective dipolarophiles in 1,3-dipolar cycloadditions with nitrones and azomethine ylides, respectively, providing fluoroalkyl isoxazolidines 3-12 and pyrrolidines 13-14 in good to excellent yields, with nearly complete regiocontrol and total diastereocontrol in favor of the isomers having anti-configuration of the nitro- and fluoroalkyl-substituted carbon centers. The 3.4-cis-cycloadducts were generally produced in higher ratios. In the case of chiral nitrones, such as 2e, very high diastereocontrol in favor of the endo bicyclic cycloadduct 11 was observed. Interestingly, in most cases the chlorodifluoro nitroalkene 1b was found to afford the best diastereocontrol. (C) 2009 Elsevier Ltd. All rights reserved.