Imidazolium-dithiocarboxylate zwitterions catalysed ring-opening additions of cyclopropenones

Imidazolium-dithiocarboxylate zwitterions (NHC•CS2), a novel organocatalyst that derived from N-heterocyclic carbene (NHC), was used to activate cyclopropenones. Under the catalysis of 10 mol% NHC•CS2, a range of phenols, alcohols, primary and secondary amines react with cyclopropenones to produce trisubstituted α, β-unsaturated esters and amides in 46-95% yield. More than 68 products, including 7 natural product derivatives have been synthesized through this method. Mechanism study showed NHC•CS2 act as a Lewis base to activate the C=C double bond of cyclopropenones and trigger the ring-opening reaction. HRMS analysis indicated the formation of the key adduct of NHC•CS2 and cyclopropenone. More importantly, this study demonstrated completely different catalytic activity of NHC•CS2 and NHC catalysts, the latter one cannot catalyse these reactions.