A Powerful Reagent for Synthesis of Weinreb Amides Directly from Carboxylic Acids

A powerful reagent, P[NCH(3)(OCH(3))](3) (3), for conversion of carboxylic acids directly to Weinreb amides was developed. In most cases the yields of the corresponding Weinreb amides were above 90% when P[NCH(3)(OCH(3))](3) was heated with aromatic and aliphatic carboxylic acids in toluene. The sterically hindered carboxylic acids can also give the corresponding Weinreb amides in excellent yields.