Construction of Quaternary Stereogenic Carbon Centers by the Lewis Base Catalyzed Conjugate Addition of Silyl Ketene Imines to α,β-Unsaturated Aldehydes and Ketones

Abstract

Highly site-selective Mukaiyama-Michael additions of silyl ketene imines to α,β-unsaturated aldehydes and ketones are described. The combination of silicon tetrachloride and a chiral bisphosphoramide provides an effective catalyst system for promoting the addition of silyl ketene imines to a variety of aromatic enals with high site selectivity and moderate to good diastereo- and enantioselectivity.

Lewis base - asymmetric catalysis - Michael addition - aldehydes - quaternary carbon

References and Notes

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16

See ref. 15j.

17

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18

For example, the observed selectivity could result from a single catalyst-enone complex if reaction through an achiral pathway was competitive with the catalyzed addition to form only one of the diastereomers.

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21

The crystallographic coordinates of 7 have been deposited with the Cambridge Crystallographic Data Centre (CCDC); deposition no. 776146. These data can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/data_request/cif.

22

For computational and mechanistic studies, see ref. 15g. For a full kinetic analysis, see ref. 19.