J. F. Brazier

ENANTIOSPECIFIC SYNTHESIS OF PENTACOORDINATED PHOSPHORUS COMPOUNDS X-RAYS DIFFRACTION STRUCTURE AND REACTION MECHANISM

Abstract It is shown that the synthesis of the optically active spirophosphorane 5 is enantiospecific. The structure and the configuration of the enantiomeric pure diastereoisomer, given by the reaction, has been established by X-rays diffraction. A mechanism accounting for the stereospecificity is proposed. The same selectivity has been observed for three other compounds.

ETUDE CINETIQUE DU MECANISME D'ADDITION DE L'ALCOOL TERTIOBUTYLIQUE SUR UN AMIDOPHOSPHITE BICYCLIQUE

Abstract The addition of tertiary butanol on a bicycloamidophosphite is stereospecific and leads to a bicyclophosphorane according to a second order kinetic. The activation parameters and isotopic effect were determined. These results suggest the formation of a phosphonium intermediate followed by an attack by the alcoolate anion, in agreement with the stereochemistry of the reaction.

CATIONS PHOSPHORES A BASSE COORDINATION: LES IMINOPHOSPHENIUMS N[sbnd]p[sbnd]N[dbnd]NR

Abstract The novel iminophosphenium, [(CH3)2N]2 P+=NC6H5, has been prepared by a modified Staudinger reaction. The mechanism of this process is discussed on the basis of spectroscopic studies of various derivatives of this ion.

MUTAROTATION ARISING FROM STEREOLABILE PENTACOORDINATED PHOSPHORUS

Abstract The purpose of this paper is to show that optical rotation is a convenient method for studying the intramolecular stereolability in pentacoordinated species, particularly phosphorus derivatives. In chemistry, it is difficult to present a completely new idea and we will deal with this topic under several headings.

Pentacovalent phosphorus compounds via iminophosphoranes

The reaction of phenyl azide with a PIII⇌ PV tautomeric equilibrium mixture leads to new spirophosphoranes derivatives (3a–d) bearing an exocyclic –NH·Ph group.

Optically active spirophosphoranes. Part VI. Kinetics of epimerization of the chiral skeleton unit

The diastereoisomeric spirophosphoranes (1M) and (1P) possess two elements of chirality, an optically active ligand derived from (+)-pseudoephedrine and the (±)-phosphavspironone system. The rates of epimerization of these compounds were obtained from a pure diastereoisomer [very likely (1M)] isolated by crystallization using the polarimetric kinetic method. Activation parameters at 278 K are: for (1M)→(1P);ΔG1‡= 21·44 kcal mol–1, ΔH1‡= 19·8 kcal mol–1, ΔS1‡=–5·7 cal K–1; for (1P)→(1M)ΔG–1‡= 21·10 kcal mol–1, ΔH–1‡= 19·4 kcal mol–1, ΔS–1‡=–5·9 cal K–1 mol–1. These results, compared with those obtained previously for (2M)→(2P), show that the change in the rate constant of epimerization can be large (133:1) even though the atoms surrounding phosphorus are the same. Comments on the possible structure of the transition state are presented.