ABSTRACT
Solphos (7,7'-bis(diarylphosphino)-3,3',4,4'-tetrahydro-4,4'-dimethyl-8,8'-bis-2H-1,4-benzoxazine) is a new modular atropisomeric biaryl ligand with a very attractive activity profile. A technically feasible synthesis is described allowing the synthesis of various derivatives of enantiopure ligand on a technical scale. Very good catalytic performances have been demonstrated for the following transformations: Ru-catalyzed hydrogenation of various beta-keto esters (95-99 % ee, s/c up to 100,000), of acetyl acetone (>99 % ee, dl/meso>98:2), and of an exocyclic alpha,beta-unsaturated acid (98.6 % ee, s/c 250). In several cases, the nature of the PAr(2) moiety had a significant effect on the enantioselectivity. Furthermore, Rh and Ir Solphos complexes achieved high enantioselectivities for a novel synthesis of 3,3-disubstituted phthalides and the reductive coupling of alkynes with N-sulfonyl imines, respectively.
ABSTRACT
Several novel planar chiral phosphinocyrhetrenyloxazolines have been synthesized, and their catalytic activities have been evaluated in a variety of asymmetric catalytic reactions. Preferable effects as compared to their ferrocenyl analogues have been observed in asymmetric allylic amination and asymmetric hydrosilylation, and up to 97% ee and 72% ee were reached, respectively. The Lewis basicity of the phosphorus on the ferrocene and the cyrhetrene, which contributes to their different behavior in catalysis, has been deduced by 31P NMR spectroscopy analysis, as indicated by 1J(77Se-31P) in the corresponding phosphine selenides.
ABSTRACT
A novel planar chiral cyrhetrene 1 has been identified as an efficient catalyst precursor for the asymmetric synthesis of diarylmethanol compounds 2 by phenylation of aldehydes. Compared to the corresponding ferrocene derivative, the performance of the cyrhetrene is superior or at least equally as good and gives excellent enantioselectivities even with catalyst loadings as low as 2 mol %.
