Stereo- and Regioselectivity in the Addition of Benzenetellurolate Ion to Triple Bond

Abstract

Stereo- and regioselectivity of the addition of benzenetellurolate ion (PhTeNa), formed in situ from (PhTe)₂, and NaBH₄ in ethanol, to acetylenic bonds have been studied. Its addition to monosubstituted acetylenes such as phenylacetylene, 1-octyne, and propargylic alcohols proceeded completely in a trans fashion to afford a regioisomeric mixture of the corresponding vinylic tellurides, the attack of PhTe moiety occurring mainly at the terminal carbon (terminal/internal=ca.80∼90/10∼20) except the case of phenylacetylene where the ion attacked completely the terminal carbon. No reaction was observed with 4-octyne, while diphenylacetylene afforded a low yield of the addition product. In the case of propiolic acid esters the addition of PhTe moiety occurred completely regioselectively at acetylenic β-carbon, while a small amount of cis-addition product was always formed (trans' cis= ca 95/5). Benzenetellurol(PhTeH), formed in situ by methanolysis of (phenyltelluro)trimethyl. silane, showed a very low reactivity for this addition.