Plant bioregulators, 2 - Syntheses of (+/-)- and (+)-sorgolactone, the germination stimulant from Sorghum bicolor

Syntheses of (+/-)-2a, the racemate of the structure proposed for sorgolact one, and its three racemic stereoisomers have been accomplished with confir mation of the stereostructures of the:intermediate (+/-)-10 and the final p roduct (+/-)-2a by Xray analysis. Its optically active form, (3aR,8S,8bS,2' R)-(+)2a, has also been prepared from (S)-(-)-citronellal by employing radi cal cyclization of 18 to 19 as the key step. Spectroscopic properties of th e synthetic products are compared with those reported for natural sorgolact one. Bioassays using clover broomrape (Orobanche minor) seeds have revealed that all the stereoisomers strongly stimulate their germination.