Introduction
This paper reviews a relatively new procedure for the direct and general synthesis
of urea compounds.[1] A typical method to generate urea bonds is the reaction of amines with highly toxic
phosgene. This class of compounds can also be obtained by using the Staudinger–aza-Wittig
reaction, also known as the ‘phosphine imide’ reaction. This methodology is based
on iminophosphorane chemistry and leads to the efficient formation of amide or urea
bonds, very important for safer ‘phosgene-free’ chemistry.[2] This ‘one-flask’ synthesis of urea derivatives includes the reaction of azides with
triphenyphosphine followed by the reaction of the phosphine imide intermediates with
carbon dioxide and amines (Scheme [1]).[3]
Scheme 1
