Triphenylphosphine dibromide: a simple one-pot esterification reagent

We report a one-pot, expedient protocol for the conversion of carboxylic acids to their esters using excess triphenylphosphine dibromide, base, and the alcohol. The reaction gave the esterified product in moderate-to-high yields (30-95%). For chiral acids, the reaction proceeded with little or no racemization. Use of a chiral alcohol in this transformation gave the ester with retention of configuration of the stereogenic center. Information is presented indicating that esterification proceeds through the intermediate generation of an acyloxyalkoxyphosphorane and where steric interactions play an important role in the energetics of the reaction.

We report a one-pot, expedient protocol for the conversion of carboxylic acids to their esters in moderate-to-high yields using PPh3Br2. For chiral acids, the reaction proceeded with little or no racemization.