Reactions of 2,2,2-triphenyl-2H-6,11-methanocycloundec[d]-1,2λ⁵-oxaphosphole (2-triphenylphosphoranylidenemethyl-5,10-methano[11]annulenone) and 2-triphenylphosphoranylidenemethyltropones with heterocumulenes have been studied to provide evidence for a P–O bonding oxaphosphole structure and to explore a preparative method for annulated heterocycles.