Exocyclic P-C vs. Endocyclic P-P Bond Cleavage in 1,2-Diphosphetes. A Competition between Cyclic Delocalization and Cyclic Strain Controlled by the Substitution Pattern
Attack by lithium on 1,2-diphenyl-3,4-di-R-substituted-1,2-diphosphetes takes place on the endocyclic P-P bond when R=Ph whereas it takes place on the exocyclic P-Ph bond when R=tBu; in this latter case, a 1,2-diphosphet-1-yl anion is obtained which is probably stabilized by cyclic delocalization.