P-chiral phosphorus heterocycles: a straightforward synthesis

Abstract

A straightforward synthesis of P-chiral polycyclic 7-phospha-norbornenes via an asymmetric Diels-Alder reaction is presented. The employed starting materials are cheap, easily accessible and of structural diversity facilitating a new flexible route towards differently functionalised P-chiral phosphanes.

[​4+2] versus [​2+2] Homodimerization in P(V) Derivatives of 2,4-Disubstituted Phospholes

“…Whereas 3,4disubstituted phospholes are prone to homodimerization, 2,5-disubstituted phospholes are stable towards this reaction. The latter can nevertheless react under more stringent conditions with other dienophiles [37]. In our case, the 2,4-disubstituted phosphole oxides are just borderline: with aryl groups and the bulky, but flexible trimethylsilyl groups homodimerization occurs, albeit slowly, whereas the bulky tbutyl group prevents this reaction.…”

P-chiral 1-phosphanorbornenes: from asymmetric phospha-Diels–Alder reactions towards ligand design and functionalisation

“…The thiophosphole group of 17 can now be employed in other asymmetric Diels-Alder reactions. 15 The basicity of lithium phosphanides like LiPPh 2 can be reduced by coordination to borane. Accordingly, LiP(BH 3 )Ph 2 gave access to 18 in good yield.…”

“…15 The basicity of lithium phosphanides like LiPPh 2 can be reduced by coordination to borane. Bromination of 13a with Br 2 PPh 3 gave bromide 15 in excellent yield.…”

Synthesis of P,P-bidentate caged phosphines via tungsten pentacarbonyl-promoted cycloaddition reactions of 1-alkyl-1,2-diphospholes

“…[13][14][15][16] The key structural feature of such phosphines is their rigid bi-or polycyclic framework, which eliminates the conformational flexibility inherent in other monocyclic chiral phosphines and represents a valuable motif for chiral ligand design. The efficiency of these ligands, featuring a chiral, nonracemizable bridgehead phosphorus atom was initially demonstrated by F. Mathey et al 17 The asymmetric [4+2] Diels-Alder cycloaddition reactions of 1-monophospholes [18][19][20] and 1,2diphospholes [21][22][23][24] with various dienophiles have become a classical approach to such rigid polycyclic phosphines. Using chiral Al 25 or Pd 26 complexes as the reaction promoters for the asymmetric [4+2] cycloaddition of monophospholes and 2-phosphindolizine has enabled the synthesis of a library of coordinated P-chiral phosphines.…”