Azaphospholes : Synthesis and Some Reactions - A Brief Account

Abstract

Azaphospholes are five-membered 60 aromatic heterocycles formed by replacement of one -CH= moiety of pyrrole ring by -P=. During the last ten years we have developed three general synthetic routes, namely [4+ 1] cyclocondensation, [3+2] cyclocondensation and 1,5-electrocyclization for the annulated azaphospholes. We have successfully carried out electrophilic substitution, namely bromination and dichlorophosphinylation at the á-position

of phosphorus, 1,2-addition at >C=P- bond including [2+4] cycloaddition, [1 +4] cycloaddition with <i style="mso-bidi-font-style:normal">o</i>-quinones at phosphorus and coordination through s2,e3 phosphorus to the metal carbonyls. Computational calculations have also been done to study structure and reactivity. The aromatic structures of 2-phosphaindolizines and related systems have been confirmed by <i style="mso-bidi-font-style:normal">ab initio</i> calculations. Furthermore, the existence of negative hyperconjugation has been

proved in the pyridinium dichlorophosphinomethylides. Feasibility of Diels-Alder reactions of azaphospholes has been studied with the help of semiempirical as well as <i style="mso-bidi-font-style: normal">ab initio</i> computational quantum calculations.