Alkylation and cyclopentannulation of phospholene derivatives

The deprotonation of 1-phenyl-3-phospholene 1-oxide, 1-sulfide or 1-borane with 1 or 2 equiv of LDA, followed by quenching with electrophiles gave a range of 2-mono- or 2,5-disubstituted phospholene derivatives in good yield. Only trans substitution in relation to the P-Ph group was observed. Treatment of lithiated phospholene intermediates with 1,3-dihaloalkanes afforded annulated 2-phenyl-2-phosphabicyclo[3.3.0]oct-3-ene derivatives. The annulation reactions occurred with high regio- and stereoselectivity and led to the exclusive formation of the exo-Ph-P substituted products.