Asymmetric Addition of Aldehydes and Ketones to Chiral 2-Azapentadienyl Lithium Compounds: Diastereoselective Synthesis of 4-Vinyl-4,5-dihydro-oxazoles

Abstract

Chiral 2-azapentadienyl lithium compounds 1, easily available by deprotonation of the corresponding N-allylimines 2, react with symmetrical and asymmetrical ketones and aldehydes to form new chiral, vinyl-substituted 4,5-dihydro-oxazoles 3. The structural properties of 1 in the gas phase and in solution were studied by quantum chemical calculations and NMR spectroscopy. The X-ray diffraction structure of 4,5-dihydro-oxazole 3d indicates the formation of a benzhydrol adduct. The new reactions are interpreted in terms of regioselective, stepwise additions of the carbonyl compounds to carbon atom C3 of 1 and subsequent removal of the chiral nucleofugal group.

addition reactions - asymmetric synthesis - chiral 2-azapentadienyl lithium compounds - chiral 4,5-dihydro-oxazoles - heterocycles

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Details of the quantum chemical calculations (GAUSSIAN 98 archive entries) may be obtained from E.-U.W. upon request.

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Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-151211. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax:[phone]; E-mail: [e-mail]).

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Programs used: Data collection: Express; Nonius B. V., 1994.- Data reduction: MolEN: Fair, K. Enraf-Nonius B. V., 1990. - Structure solution: SHELXS-86 and SHELXS-97: Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467-473.- Structure refinement: SHELXL-97: Sheldrick, G. M. Universität Göttingen, 1997. - Graphics: SCHAKAL: Keller, E. Universität Freiburg, 1997.