gem-Difluorosubstituted NH-azomethine ylides in the synthesis of 4-fluorooxazolines via the three-component reaction of imines, trifluoroacetophenones and CF2Br2

1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives

“…In contrast, the corresponding alkynyl esters and alkynyl ketones resulted in selective addition to the alkyne triple bond. The cycloaddition of gem-difluorosubstituted NH-azomethine ylides with α,α,α-trifluoroacetophenones 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), CBr2F2, Pb filings and tetrabutylammonium bromide, and resulted in isolation of the fluoro-oxazolines 238 after chromatography on silica (Scheme 67, Table 31).…”

“…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).…”

Recent progress in the use of fluoroorganic compounds in pericyclic reactions

“…96 This method has provided entry to a new class of fluorinated heterocycles, 4-fluoro-3-oxazolines, starting from difluorinated NH-azomethine ylides and trifluoroacetophenones (Scheme 37). 97 Azomethine ylides 55c with the C-N bond constrained in an aziridinum ring can also be generated from the appropriate 3-aryl-2H-azirines (Scheme 38). 98 These reactive intermediates react with DMAD and benzaldehyde regioselectively, giving difluorinated [5,3]-fused heterocycles as cycloadducts, which are amenable to transformations in which the aziridine ring can be preserved.…”