Stereoselective synthesis of (R)-(+)-1-methoxyspirobrassinin, (2R,3R)-(-)-1-methoxyspirobrassinol methyl ether and their enantiomers or diastereoisomers

Stereoselective synthesis of cruciferous indole phytoalexin (R)-(+)-1-methoxyspirobrassinin and its unnatural (S)-(-)-enantiomer was achieved by spirocyclization of 1-methoxybrassinin in the presence of (+)- and (-)-menthol and subsequent oxidation of the obtained menthyl ethers. Methanolysis of menthyl ethers in the presence of TFA afforded (2R,3R)-(-)-1-methoxyspirobrassinol methyl ether as well its unnatural (2S,3S)-, (2R,3S)-, and (2S,3R)-isomers. (C) 2007 Elsevier Ltd. All rights reserved.