Novel results obtained by freezing berry pseudorotation of phosphoranes (10‐P‐5)

By freezing Berry pseudorotation of spirophosphoranes with recourse to the rigidity of the Martin bidentate ligand, we successfully prepared configurationally stable enantiomeric pairs of optically active phosphoranes, and could isolate “anti‐apicophilic” C‐apical O‐equatorial (O‐cis) phosphoranes. The effect of σ*_{P O} orbital of the O‐cis phosphorane was investigated both experimentally and theoretically. O‐cis phosphoranes were revealed to be much more electrophilic at the phosphorus atom than O‐trans isomers by experimental studies. The acidity of the α‐proton of an O‐cis benzylphosphorane was found to be higher than that of the corresponding O‐trans isomer. By the reaction of the α‐carbanion of an O‐cis benzylphosphorane with PhCHO, we succeeded in the first isolation and full structural characterization of a 12‐P‐6 phosphate bearing an oxaphosphetane ring, the intermediate in the Wittig type reaction using a 10‐P‐5 phosphorane. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:390–396, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10072