Cu(I)-catalyzed regioselective synthesis of pyrazolo[5,1-c]-1,2,4-triazoles.

Cycloadditions of terminal alkynes to 1,2,4-triazolium N-imides in the presence of base and Cu(I) afford pyrazolo[5,1-c]-1,2,4-triazoles regioselectively. The scope of alkynes, the influence of the electronic nature of the leaving group, and variations in the 1-alkyl substituent were examined. Quantum chemical calculations were employed to explain the distinct reactivity of the propiolates.

Long-range intramolecular S → N acyl migration: a study of the formation of native peptide analogues via 13-, 15-, and 16-membered cyclic transition states.

The intramolecular long-range S → N acyl migration via 13-, 15-, and 16-membered cyclic transition states to form native tetra- and pentapeptide analogues was studied on S-acylcysteine peptides containing ß- or γ-amino acids. The pH-dependency study of the acyl migration via a 15-membered cyclic transition state indicated that the reaction is favored at a pH range from 7.0 to 7.6. Experimental observations are supported by structural and computational investigations.