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
