A facile carbene route to 2-fluoro-2-pyrrolines via fluorinated azomethine ylides

2-Fluoro-2-pyrrolines have been prepared by a domino reaction of difluorocarbene with N-substituted ketimines in the presence of fumaronitrile, malenitrile or dimethyl maleate, involving azomethine ylide formation, 1,3-dipolar cycloaddition, and dehydrofluorination. The reactions of 1H-dibenzo[b,e]azepine and 3,4-dihydroisoquinolines with difluorocarbene in the presence of fumaronitrile proceed with the formation of fluorinated 1H-dibenzo[c,f]pyrrolo[1,2-a]azepine and pyrrolo[2,1-a]isoquinoline derivatives. The yields of 2-fluoro-2-pyrrolines depend mostly on their resistance to chromatographic work-up and are higher for 5,5-disubstituted pyrrolines compared to 5-monosubstituted derivatives.