Stable optically pure phosphino(silyl)carbenes: reagents for highly enantioselective cyclopropanation reactions.
The stability of phosphino(trimethylsilyl)carbenes bearing cyclic diamino substituents on phosphorus is strongly dependent on the steric hindrance of the nitrogen substituents. Phosphinocarbenes 3 and 7, derived from the trans-N,N'-diisopropylcyclohexane-1,2-diamine and N,N'-diisopropyl-1,2-ethanediamine, are not observed; instead the 1,3-diphosphete 4 and a novel six-membered heterocycle 8, which results from the dimerization of 3 and the reaction of 7 with its diazo precursor 6, respectively, have been isolated. In contrast, the phosphino(silyl)carbene 14 derived from N,N'-di-tert-butyl-1,2-ethanediamine has been isolated in high yield. By using the enantiomerically pure (S,S)-, and (R,R)-N,N'-di-tert-butyl-1,2-diphenyl-1,2-ethanediamines, the first optically pure phosphino(sily)carbenes (S,S)-17 and (R,R)-17 have been prepared. They react with methyl acrylate to give the corresponding cyclopropanes (S,S,R,R)-19 and (R,R,S,S)-19 with a total syn diastereoselectivity and an excellent enantioselectivity (de>98 %).
Krysiak
Jerzy
J
Laboratoire Hétérochimie Fondamentale et Appliquée, UMR 5069, Université Paul Sabatier, 118, route de Narbonne, 31062 Toulouse Cedex 04, France.
Lyon
Céline
C
Baceiredo
Antoine
A
Gornitzka
Heinz
H
Mikolajczyk
Marian
M
Bertrand
Guy
G