Selective tellurium-mediated synthesis of optically active E- or Z-allyl alcohols from optically active epoxy alcohols

摘要

Threo- and erythro- epoxy alcohols are converted in high yield to trans- and cis-allyl alcohols, respectively. The threo epoxy alcohol or erythro-epoxy alcohol is reacted with a toluenesulfonic anhydride to form a threo- or erythro- glycidyl tosylate. The glycidyl tosylate is contacted with tellurium ion, in the form, e.g. of Na.sub.2 Te that has been prepared by adding tellurium in elemental form and sodium borohydride or lithium triethyl borohydride to dimethylformamide (DMF). The DMF has a low volatility and permits further work to be carried out at elevated temperatures. The glycidyl tosylate is added to the sodium telluride in DMF, and is permitted to react. The tellurium ion displaces the tosylate and opens the epoxide to form an unstable alkoxy epitelluride. This epitelluride is a short-lived intermediate, and extrudes the tellurium, leaving the olefin. The opening of the epoxide required the adoption of an anti configuration. Consequently, erythro starting compounds yield cis-allyl alcohols exclusively; threo starting compounds yield trans-allyl alcohols exclusively. If the starting compounds are optically active, the products are also optically active.