Synthesis of spiroindoline phytoalexin ( S )-(−)-spirobrassinin and its unnatural ( R )-(+)-enantiomer

The stereoselective syntheses of the cruciferous indole phytoalexin (S)-(−)-spirobrassinin and its unnatural (R)-(+)-enantiomer were achieved by bromine-induced spirocyclization of (−)- and (+)-1-(8-phenylmenthoxycarbonyl)brassinin in the presence of water to give the corresponding spirobrasinol derivatives, followed by oxidation to the derivatives of spirobrassinin and finally removal of the chiral auxiliary.