A [2+2] cycloaddition route to dimethylaminomethylene vinamidinium salts

Trifluoropropanoic acid reacts with 1 equiv of POCI3 in DMF to generate the trifluoromethyl enamine (7). At this stage, two reaction manifolds are available. The expected reaction with additional POCI3 generates the 2-trifluoromethyl vinamidinium salt (3c). However, thermally driven loss of fluoride generates an iminium ion, which sets the stage for a [2 + 2] cycloaddition to ultimately generate the dimethylaminomethylene vinamidinium salt (1).