Synthesis of Annelated Phospholes through Intramolecular CH Activation by Monovalent Phosphorus

Electrophilic terminal phosphinidene complexes [Ar‐Ar‐P‐W(CO) 5 ] (Ar‐Ar: biaryl or an analogue thereof) undergo a spontaneous insertion of the phosphorus atom into the vicinal CH bonds to give annelated phospholes. Twelve examples are described, including biphenyl, thienyl, pyrrolyl, and benzofuryl groups as biaryl moieties. The activation energy of the insertion reaction is quite low (about 2 kcal mol −1 ).