Synthesis and dynamic NMR study of spiroheterocycles containing a 1,2,4-triazolidine moiety

摘要

A one-pot synthesis of spiro-heterocyclic systems containing a 1,2,4-triazolidine moiety via 1,3-dipolar cycloaddition reaction of azomethine ylides (generated in situ from alpha-amino acids and ninhydrin) with diisopropyl azodicarboxylate in 50% aqueous MeOH at room temperature, is described. The structure of a typical product was confirmed by X-ray crystallography. The H-1 NMR spectra of diisopropyl 1,3-dioxo-1,3-dihydrospiro[indene-2,3 '-[1,2,4]triazolidine]-1 ',2 '-dicarboxylate exhibited dynamic NMR effects, which were attributed to the fast positional change of the ester groups and their interaction with N-H as well as with methylene protons, and restricted bond rotation of the carbamate groups. The calculated free-energy of activation (Delta G(#)) for these dynamic processes are 64 +/- 2 kJ mol(-1) and 55 +/- 2 kJ mol(-1), respectively. Graphic abstract