REACTION OF BETA-ETHYLTHIOPROPIONYL TETRAFLUOROBORATES WITH ALKYNES -STEREOSPECIFIC ONE-POT SYNTHESIS OF 1-ETHYLTHIOPENT-1,4-DIEN-3-ONES

A stereospecific one-pot synthesis of 1-ethylthiodivinylketones is des cribed. Reaction of different alkynes with beta-ethylthiopropionyl tet rafluoroborate proceeds through formation of six-membered cyclic sulfo nium salts as a conjugated addition of acyl and sulfide moieties to ac etylene. Subsequent cleavage of sulfonium salts with bases results in the corresponding 1-ethylthiodivinylketones. The reaction proceeds reg io- and stereospecifically as syn-addition of acryloyl and ethylthio g roups to the triple bond.