Asymmetric synthesis of metallocenes with planar and central chirality by rhodium-catalyzed desymmetrization reactions†

Abstract

Metallocenes with planar and central chirality have emerged as a privileged skeleton for chiral ligand design, and such ligands have exhibited tremendous success in various asymmetric catalysis protocols. Herein, we report a rhodium/chiral diene-catalyzed asymmetric desymmetrization of 1,2-diformylmetallocenes with aryl/alkenylboronic acids to give enantio-enriched formylmetallocenes, which are diastereoisomers of Ugi-type products. This catalytic system also enables the kinetic resolution of 2-substituted 1-formylferrocene with a selectivity factor (s) of up to 4331. Compared with traditional synthesis methods, our method has the following advantages: (1) opposite diastereoselectivity; (2) catalytic asymmetric synthesis; (3) single-step construction of planar and central chirality. The synthetic utility of the present method is demonstrated by the asymmetric synthesis of a series of chiral phosphine ligands, including Josiphos- and PPFA-type ligands.