Intramolecular cyclization of isothiocyanyl amino acids/peptide: arrival at unnatural thioxoimidazolidinyl/thioxooxazolidinyl amino acids.

A novel intramolecular cyclization of isothiocyanyl amino acids/peptide is reported to arrive at unnatural thioxoimidazolidinyl (TOI)/thioxooxazolidinyl (TOO) amino acids for the first time. Interestingly, analogous isothiocyanyl amines under a similar reaction condition either follow 5-endo-dig cyclization to offer 5-membered thiourea or acyclic diethylaminyl thiourea derivative instead of 6-membered cyclic thiourea.