Organic Phosphazene Bases and their Utilization in Organic Chemistry

Abstract

Organic non-ionic bases play an important role in organic synthesis. Using them, some reactions can be carried out in mild conditions, e.g. at lower temperatures, and thus the possibility of side reactions is decreased. This is especially important in stereoselective synthesis. Their favourable properties can be due to better solubility in organic solvents and/or to increased reactivity of anions ("naked" anions). The basicity of five investigated aminophosphazene bases is high because of extensive delocalization of positive charge in their conjugated acids and is comparable or higher than that of strong, commonly used bases - LDA or BuLi. All the bases except one are weak nucleophiles. The simplest method for the synthesis of aminophosphazenes is the reaction of Cl₃P=NR with a suitable dialkylamine. Some of the bases are commercially available, neat or in hexane or THF solutions. Also, some nitrogen bases - DBU, DBN, TBD, MTBD and PMG - are compared.