Effect of σ* P--O Orbital on Structure, Stereomutation, and Reactivity of C -Apical O -Equatorial Spirophosphoranes

Effect of † * P--O orbital of C-apical O-equatorial (O-cis) spirophosphorane was investigated both experimentally and theoretically. O-cis phosphoranes revealed to be much more electrophilic on the phosphorus atom than O-trans isomers by experimental studies. Theoretically, the energy of the † * P--O orbital of O-cis phosphorane was calculated to be lower than that of the † * P--C orbital of O-trans phosphorane by 18.7 kcal/mol, and the result supports the enhanced electrophilicity of O-cis spirophosphoranes compared with O-trans isomer.