PC–N and P–CN type 1,3-azaphospholes – comparing the chemistry of π-excess aromatic 1H- and non-aromatic 3H-isomers and the influence of anellation (A personal account)

Abstract

A short overview of the work on unsaturated five-membered EC–N and E–CN heterocycles, initially with EAs, later EP, and related research is given. Principal synthetic strategies to non-, carbo- and heterocyclic (C–C-bridge) anellated 1,3-azaphospholes, properties, electronic structures and reactions with organic and transition-metallic electrophiles without and with prior lithiation by tert-butyllithium are presented and illustrate the different chemistry of the aromatic 1H- and non-aromatic 3H-1,3-azaphosphole-type heterocycles. Various open questions are addressed in the outlook. Some references to the chemistry of related C-N-bridged heterocyclic anellated 1,3-azaphospholes, reviewed by Bansal, are also included.

GRAPHICAL ABSTRACT

Keywords:

• P heterocycles
• Pi-excess aromaticity
• lithiation
• electrophilic substitution
• coordination modes
• homogenous catalysis