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.