Catalytic Hydrothiolation: Counterion-Controlled Regioselectivity

In this Article, we expand upon the catalytic hydro­thiolation of 1,3-dienes to afford either allylic or homoallylic sulfides with high regio­control. Mechanistic studies support a pathway in which regio­selectivity is dictated by the choice of counterion associated with the Rh center. Non-coordinating counterions, such as SbF<sub>6</sub><sup>–</sup>, allow for η<sup>4</sup>-diene coordination to Rh complexes and result in allylic sulfides. In contrast, coordinating counterions, such as Cl<sup>–</sup>, favor neutral Rh complexes in which the diene binds η<sup>2</sup> to afford homoallylic sulfides. We propose mechanisms that rationalize a fractional dependence on thiol for the 1,2-Markovnikov hydro­thiolation while accounting for an inverse dependence on thiol in the 3,4-<i>anti</i>-Markovnikov pathway. Through the hydro­thiolation of an essential oil (β-farnesene), we achieve the first enantio­selective synthesis of (−)-agelasidine A.