Thiol–Yne Coupling of Propargylamine under Solvent-Free Conditions by Bond Anion Relay Chemistry: An Efficient Synthesis of Thiazolidin-2-ylideneamine

Thiol-yne coupling of propargylamine with isothiocyanate has been developed under metal- and solvent-free conditions. The addition of propargylamine to isothiocyanate gives propargylthiourea. This intermediate in situ undergoes intramolecular 5-exo-dig cyclization to give thiazolidin-2-ylideneamine. A through-bond anion relay reaction occurs by attack of the sulfur (not the nitrogen) atom on the alkyne in a highly regioselective manner at ambient temperature. Wide varieties of thiazolidin-2-ylideneamine derivatives were formed in excellent yields.