Synthesis of Enantioenriched and Diastereomerically Pure cis-Fused Bicyclic α-Oxy-Substituted γ-Lactones via Epoxidation of Optically Active Homoaldol Products

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

References

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  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.) [phone]; E-mail: [e-mail]].

1

Responsible for X-ray structure data.