Synthesis of Dipeptide, Amide, and Ester without Racemization by Oxalyl Chloride and Catalytic Triphenylphosphine Oxide

An efficient triphenylphosphine oxide-catalyzed
amidation and esterification
for the rapid synthesis of a series of dipeptides, amides, and esters
is described. This reaction is applicable to challenging couplings
of hindered carboxylic acids with weakly nucleophilic amines or alcohols,
giving the products in good yields (67–90%) without racemization.
This system employs the highly reactive intermediate Ph3PCl2 as the activator of the carboxylate in a catalytic
manner and drives the reaction to completion in a short reaction time
(less than 10 min).