Abstract
By applying the (-)-sparteine-mediated asymmetric deprotonation to 1-O -(2-alkylcycloalk-1-enyl)methyl N ,N -diisopropylcarbamates, combined with a lithium-titanium exchange followed by addition to achiral aldehydes, enantioenriched homoaldol products 6 were prepared. Hydroxyl-directed epoxidation resulted in the cleavage of the oxirane ring by the migration of the N ,N -diisopropylcarbamoyloxy group to form bicyclic γ-lactols 10 via the corresponding γ-hydroxy aldehydes. After oxidation, diastereomerically pure, penta-substituted γ-lactones 11 were obtained.
Key words
carbamates - aldol reactions - sparteine - diastereoselectivity - epoxides - bicyclic compounds - lactones
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12h CCDC-264379, 264380, and 264831 contain the supplementary crystallographic data for this paper. This data can be obtained free of charge at www.cam.ac.uk/conts/retrieving.html [or from Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (internat.) +44 (1223)336-033; E-mail: deposit@ccdc.cam.ac.uk].