Asymmetric synthesis catalyzed by metal complexes containing chiral 1,6-Diamino-Spiro[4,4]nonane or its derivatives

Abstract

Chiral phosphine ligands have played a dominant role in the development of novel transition-metal-catalyzed enantioselective synthesis. Among these evolved ligands, the type of ligands containing skewed backbone and with C₂symmetry has been fcund to be highly effective and versatile in inducing the metal-catalyzed asymmetric transformations. In addition, the ligands having rigid conformational structures seem generally to be better than those which are conformationally mobile in asymmetric catalytic reactions. The results also unveil that a sterically asymmetric environment created by the chiral ligands should be the main factor responsible for the high enantioselectivity. From this point of view, the derivatives of the intrinsically skewed spirocyclic diol have attracted our attention because of the potentially useful rigid chiral backbone. Therefore, the preparation of optically pure spirodiols and subsequently various transformations of the cis.cis-spiro[4,4]nonane-l.6-diol to chiral auxiliaries such as organophosphines and amines have been studied. The further development of the novel chiral ligands applying spiro-derivatives as the backbone and practical utility of the spiro-containing catalysts in some asymmetric catalytic reactions are the focal point of the research. The desired optically active cis,cis-l,6-diamino-spiro[4,4]nonane has been prepared successfully and transformed to corresponding cis,cis-l,6-Bis(diphenylphosphino-amino)spiro[4,4]nonane. This novel chiral aminophosphine was proven to give a highly efficient Rh(I) catalyst for the asymmetric hydrogenation of dehydro 帢-amino acid esters and showed excellent enantioselectivities ranged from 94 to over 99% ee. The hydrogenation of methyl enol acetate and ethyl enol acetate catalyzed by the same Rh(I) catalyst gave the enantioselectivities of 96.2 and 96.7% respectively. Furthermore, the hydrogenation of dimethyl itaconate catalyzed by the spirodiaminophosphtne-Rh(I) complex resulted the hydrogenated dimethylsuccinate with 93% ee. In general, the spirodiaminophosphine was verified to be a selective and efficient ligand for the asymmetric hydrogenation of various types of prochiral olefms. The mono- and disulfonamide derivatives of C2-symmetric spirodiamine were applied to the transfer hydrogenation reactions of aromatic ketones and the alkylation reactions of aldehydes. The RuII(庢6-arene)[N-(p-tolylsulfonyl)-spirodiamine]Cl complexes were found to be fairly efficient catalysts for the asymmetric transfer hydrogenation of aromatic ketones but with modest enantioselectivities. Nevertheless, more successful results were achieved in the asymmetric alkylation of aldehydes with the monotosylated derivative of spirodiamine. Up to 94% ee was obtained in the addition of diethylzinc to benzaldehyde with a catalytic amount of N-(p-tolylsulfonyl)spirodiamine as the chiral auxiliary.