Addition of dithi(ol) anylium tetrafluoroborates to α, β-unsaturated ketones

In the presented study, dithi(ol) anylium tetrafluoroborates are added to alpha, beta-unsaturated ketones in a Michael-type reaction yielding diverse substituted ketene diothi(ol) anes. The reactions proceed at room temperature in 1 or 13 h without the need of further additives. The presented procedure is in particular useful for dithi(ol) anylium tetrafluoroborates without electron-withdrawing groups in alpha-position. This is advantageous with respect to previous approaches, which were limited to the use of ketene dithioacetals substituted with electron-withdrawing groups. Aiming for the systematic investigation of possible steric and electronic influences on the outcome of the reaction, various combinations of electrophiles and nucleophiles were used and the results of the reactions were compared based on the type of the used dithioacetal. The scope of the presented procedure is shown with four additional transformations including the use of additional electrophiles and nucleophiles, the use of a chiral auxiliary and subsequent reduction of selected products. Additionally, we extended the reaction to the synthesis of diene dithiolanes by addition of an ynone to alpha-alkyl or aryl-substitued dithiolanylium TFBs.