Unexpected transformation of 3-amino-4,4,4-trifluoro-1-phenylbut-2-en-1-one into 2,6-diphenyl-4-trifluoromethylpyridine

On heating in glacial acetic acid (or ethanol in the presence of manganese(ii) acetate), 3-amino-4,4,4-trifluoro-1-phenylbut-2-en-1-one undergoes unusual transformation into 2,6-diphenyl-4-trifluoromethylpyridine. The regioisomeric β-aminovinyl ketone, viz. 1-amino-4,4,4-trifluoro-1-phenylbut-1-en-3-one, remains unchanged under similar reaction conditions.