Reaction of the a-Benzylic Anion of Spirophosphoranes with N,a-Diphenylnitrone: Stereochemistry and Formation of Hexacoordinate Phosphate Bearing a 1,2,5-Oxazaphospholidine Ring

The benzylic anion (3a-Li) a to the phosphorus atom generated from C-apical O-equatorial (O-cis) spirophosphorane (la) reacted with N,a-diphenylnitrone to give hexacoordinate phosphates (8) bearing a 1,2,5-oxazaphospholidine ring. The phosphates were characterized by 3 1 P NMR and by the structure of the products of protonolysis. Examination of the corresponding reactions from O-apical C-equatorial (O-trans) isomer (2a) revealed that the phosphates (9) derived from 2a were unstable compared with the hexacoordinated 8 derived from la, mainly due to the stabilizing trans influence of the P-O bond in 8.