Synthesis of 3-(2,2,2-trifluoroethylidene)-lactams. First examples of 1,3-dipolar cycloaddition with diazomethane and N-methyl-α-phenylnitrone
The preparation of 3-(2,2,2-trifluoroethylidene)-lactams 7–9 is accomplished by reduction of 3-trifluoroacetyl-substituted lactams 1–3 and subsequent dehydration of trifluoromethylated methanols 4–6. 1,3-Dipolar cycloadditions of compounds 7 with diazomethane and N-methyl-α-phenylnitrone give spirocyclic pyrazoline 11 and isoxazolidine 12. The structure of the latter heterocycle is confirmed by X-ray diffraction analysis and by comparison of 19F and 13C NMR data.