Synthesis of enamides

Abstract

(Z)-3-Arylprop-2-enoic acids can be converted by the Curtius procedure, through the acyl azides, into (Z)-2-arylethenyl isocyanates, which with methanol give methyl (Z)-N-(2-arylethenyl)carbamates. Acylation of the (Z)-enecarbamates, through their anions, leads to methyl (Z)-N-acyl-N-(2arylethenyl)carbamates, which on treatment with lithium iodide in boiling N,N-dimethylformamide or acetonitrile undergo demethoxycarbonylation to give (Z)-enamides. This stereospecific route to enamides can also be used in the E-series. Treatment of (Z)- or (E)-2-arylethenyl isocyanates with trifluoroacetic acid gives (E)-N-(2-arylethenyl)trifluoroacetamides, the anions of which, with acylating agents, give (E)-enamides directly.