Synthesis of various acylating agents directly from carboxylic acids

A straightforward synthesis of acylating reagents such as Weinreb and MAP amides from aromatic, aliphatic carboxylic acids, and amino acids using PPh3/NBS combination is described. A chemo-selective modification of the carboxylic acid group into Weinreb amide in the presence of more reactive aldehydes and ketones is presented. All reactions were performed at ambient temperature under air using undried commercial grade solvent. Furthermore, the present methodology could be performed at a gram scale under inert-free reaction conditions. In addition, 7-azaindoline amide auxiliary (used for catalytic asymmetric aldol- and Mannich-type reactions), which behaves like Weinreb amide is also synthesized under similar reaction conditions.