Annulated Heterophospholes

Organophosphorous compounds have widespread use not only in medicines, agriculture and industry but they also find important applications in academic research in organic syntheses. In view of interesting chemistry of such compounds and their wide applications a systematic study of annulated heterophospholes has been undertaken. Annulated heterophospholes may be visualized to be derived from the typical fused heterocyclic systems such as indoles, indolizines, benzimidazole, etc by a CH/P exchange in the five membered ring. The present study was undertaken to explore the synthesis, reactivity and quantum chemical calculations of 2-phosphaindolizines in a broader aspect. Eight new representatives of 2-phosphaindolizines were synthesized through [4+1]cyclocondensation of N-alkylpyridinium bromides. Chemical reactivity of some of these compounds towards electrophilic substitution, H2S/S8 and oxidation with tetrachloro-o-benzoquinone were investigated. The structures of various synthesized products have been elucidated with the help of extensive NMR (31P,1H and 13C ¿ NMR) studies and elemental analysis.