Synlett 2005(4): 611-614  
DOI: 10.1055/s-2005-862392
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Homo-Proline Tetrazole as an Improved Organocatalyst for the Asymmetric Michael Addition of Carbonyl Compounds to Nitro-Olefins

Claire E. T. Mitchell, Alexander J. A. Cobb, Steven V. Ley*
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
Fax: +44(1223)336442; e-Mail: svl1000@cam.ac.uk;
Further Information

Publication History

Received 22 December 2004
Publication Date:
22 February 2005 (online)

Abstract

A new homo-proline tetrazole derivative 7 has been prepared and shown to have improved properties for achieving asymmetric Michael addition of carbonyl compounds to nitro-olefins.

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9

Typical Experimental Procedure.
To a suspension of catalyst (15 mol%) and nitro-olefin (0.5 mmol) in an i-PrOH-EtOH mix (1:1, 2 mL) was added ketone (0.75 mmol, 1.5 equiv) and the resulting mixture stirred at 20 °C for 24 h. After this time the reaction was quenched with sat. NH4Cl (2 × 20 mL) and the aqueous phase extracted with EtOAc (2 × 25 mL). The combined organic layers were dried (MgSO4), filtered and evaporated to give a residue which was further purified by flash column chromatography using EtOAc and petroleum ether 40-60 as eluent.

12

This was proven by comparison of chiral HPLC retention times and also by an inversion of sign in the optical rotation as compared to literature.