New, Readily Available Organocatalysts for the Enantioselective Reduction of α-Imino- and β-Imino Esters

Abstract

Novel metal-free, readily available chiral catalytic systems for the enantioselective reduction of keto imines are reported. Different β-imino esters were reduced by trichlorosilane in the presence of 10 mol% of a chiral Lewis base easily obtained in one step only from prolinol, in high yields and in up to 85% enantioselectivity; imines bearing an inexpensive and removable chiral auxiliary, were reduced with complete control of the absolute stereochemistry. The methodology was successfully extended to the stereoselective synthesis of α-amino esters.

Key words

trichlorosilane - Lewis base - β-imino esters - stereo­selective reduction - imines

References and Notes

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  See also ref. 2.

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  See also ref. 5.

10

For the preparation of different enamines and the assignment of absolute stereochemistry of reduction products see the details in Supporting Information.

11

Deprotection of N-PMP was effectively accomplished with CAN in MeCN at 0 ˚C (see Supporting Information for experimental details).

13

The favorably match or mismatch combinations of chiral amine auxiliary and catalysts have been already clarified in ref. 5b.