ortho-Acidic aromatic thiols as efficient catalysts of intramolecular Morita–Baylis–Hillman and Rauhut–Currier reactions

ortho-Mercaptobenzoic acid and ortho-mercaptophenols were discovered as efficient thiol catalysts of both the intramolecular Morita–Baylis–Hillman (MBH) and Rauhut–Currier (RC) reaction. High reaction rates were achieved under mildly basic, aqueous conditions. The unprecedented catalytic activity of these protic nucleophiles could originate from a Brønsted acid induced destabilization of intermediate thioethers and thus represent a unique mechanism of multifunctional Lewis base catalysis.