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 6 –, allow for η 4 -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 η 2 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.