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 SbF₆^–, allow for η⁴-diene coordination to Rh complexes and result in allylic sulfides. In contrast, coordinating counterions, such as Cl^–, favor neutral Rh complexes in which the diene binds η² 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-anti-Markovnikov pathway. Through the hydro­thiolation of an essential oil (β-farnesene), we achieve the first enantio­selective synthesis of (−)-agelasidine A.