Streamlined Stereoselective Entry to (-)-Quinagolide and to 3-Substituted Octahydrobenzo[ g]-Quinolines

J Org Chem. 2024 Feb 16;89(4):2649-2655. doi: 10.1021/acs.joc.3c02681. Epub 2024 Jan 27.

Abstract

A very short stereoselective synthesis of enantiomerically pure (3S, 4aS, 10aR)-quinagolide has been developed. The key steps involved are a copper-catalyzed regioselective arylation of (S)-epichlorohydrin with 1,6-dimethoxynaphthalene and a diastereoselective trans-reduction of a cyclic enamine intermediate. The possibility to use both enantiomers of epichlorohydrin and the diastereodivergency found in the reduction process paves the way for a general preparation also in the nonracemic form of chiral trans-fused 3-substituted octahydrobenzo[g]quinolines that are privileged structures in medicinal chemistry.