INTRAMOLECULAR RING-OPENING OF A 2,3-EPOXY ALCOHOL BY A XANTHATE ANIONIC CENTER - STEREOSPECIFIC PREPARATION OF 2-MERCAPTO-1,3-DIOL UNITS

Stereospecific ring openings of optically active 2,3-epoxy alcohols we re performed by the reaction of 1, 3, 5, and 7 with carbon disulfide a nd sodium hydride to give the five-membered xanthates 2, 4, 6, and 8. Both enantiomers of 2-mercapto-1,3-diol triacetates, 11 and 14, were d erived from 4 and 6, respectively. The ring opening reaction proceeded at -78-degrees-C to -30-degrees-C, and the yields were around 80%. Ho wever, at a higher temperature between 0-degrees-C to room temperature , a complicated reaction took place and led to the formation of two is omers of the cyclic thiol carbonates 15 and 16 from 1 or 5. These proc esses were also stereospecific, and mechanisms have been proposed. In the case of the 3,4-epoxy alcohol 20, the epoxide ring opening gave th e six-membered xanthate 21 stereospecifically.