“…The optimized procedure involved stirring a mixture of the imine 223c, with an excess of trifluoroacetophenone (3o), CBr2F2, Pb filings and tetrabutylammonium bromide, and resulted in isolation of the fluoro-oxazolines 238 after chromatography on silica (Scheme 67, Table 31). Presumably the imine 223c reacts with liberated difluorocarbene to afford the azomethine ylide 236 which undergoes cycloaddition with The cycloaddition of gem-difluorosubstituted NH-azomethine ylides with α,α,α-trifluoro-acetophenones has been reported to form 4-fluorooxazolidines [143]. The optimized procedure involved stirring a mixture of the imine 223c, with an excess of trifluoroacetophenone (3o), CBr 2 F 2 , Pb filings and tetrabutylammonium bromide, and resulted in isolation of the fluoro-oxazolines 238 after chromatography on silica (Scheme 67, Table 31).…”