Synthesis and Application of a New Class of Planar and Centrally Chiral Ferrocenyl Amino Alcohol Ligands

The highly enantioselective, facile, scalable, and robust synthesis of a new family (14 examples) of amino alcohol ligands possessing planar and central chirality that is described. They were applied to the diethylzinc and diphenylzinc additions to aldehydes with up to 98 % yield and 99 % ee and 82 % yield and 88 % ee, respectively.

Abstract

A family of ferrocenyl amino alcohols (14 examples) has been prepared from the corresponding planar chiral ketones and evaluated as a new class of chiral ligands for asymmetric ethyl- and phenylzinc additions to aldehydes. The highly enantioselective synthesis of these ligands is facile, scalable, robust and relies on the use of cheaply available starting materials. Asymmetric ethyl additions proceeded smoothly at ambient temperature, with reaction times as short as 1 hour furnishing the desired products in up to 90 % yield and 99 % ee. The corresponding phenyl additions afforded products in up to 81 % yield and 88 % ee. The observed stereochemical outcome for the addition of diethylzinc was rationalized and the key proposed transition state was supported by an analysis of the X-ray structures of a series of amino alcohol ligands.

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