Trifluoropropenes as Dipolarophiles

Article abstract of DOI:10.1246/bcsj.66.263

The cycloaddition of C-phenyl-N-methylnitrone with 3,3,3-trifluoropropene and methyl 4,4,4-trifluoro-2-butenoate regio- and stereoselectively gave trans-2-methyl-3-phenyl-5-trifluoromethylisoxazolidine (3a) and methyl 2-methyl-c-3-phenyl-t-5-trifluoromethyl-r-4-isoxazolidinecarboxylate (3b), respectively, as major products.The cycloaddition with 3,3,3-trifluoro-1-nitropropene proceeded regiospecifically to give 2-methyl-c-4-nitro-r-3-phenyl-t-5-trifluoromethylisoxazolidine (3c) and 2-methyl-t-4-nitro-r-3-phenyl-c-5-trifluoromethylisoxazolidine (4c), stereoisomer with 3,4-cis-configuration being predominantly produced.This regioselectivity is explained by both the nitrone-HOMO controlled orbital interaction and the steric hindrance in a transition state.Under more drastic conditions c-3, r-4-isoxazolidine 3b isomerized to the more stable c-3, t-4- and regioisomeric isoxazolidines via 1,3-dipolar cycloreversion.The similar treatment of 3c and 4c resulted in the formation of trans-1-methyl-4-phenyl-3-trifluoromethyl-2-azetidinone.