Recent Progress in 1,2,4-Triazolo[1,5-a]pyrimidine Chemistry

Abstract

Publisher Summary 1,2,4-Triazolo[1,5-a]pyrimidines (TPs) play an important role in pharmaceutics, agrochemistry, photography, and other fields. They attract attention in synthetic, analytical, and theoretical chemistry. Isomeric 1,2,4-triazolo[4,3-a]pyrimidines and partially reduced TPs are mentioned only when they are precursors, potential intermediates, or reaction products of TPs. By far, the most TP syntheses are condensations of dinucleophilic 5-amino-1,2,4-triazoles (ATs) with 1,3-bifunctional synthons as in the formation of TP 2. Quantum-chemical calculations on TPs, particularly oxo compounds, were performed by several groups. A new aromaticity index was calculated for heterocyclic compounds. Comparison of the index of 2-ribosyl-5,7-dimethyl TP with that of the isomeric compound suggests that the driving force for the Dimroth rearrangement of the latter substance is the increase in aromatic character. The chapter discusses the molecular dimensions, molecular spectra, thermodynamic properties, tautomerism, and betain and mesoionic structures of TPs. The reactivity of TPs are described including triazolopyrimidines as bases and acids, ring alkylation, electrophilic reactions at carbon ring atoms, nucleophilic addition, ring cleavage, nucleophilic substitution of functional groups at the rings introduction and transformation of individual substituents, and reactivity of side chains. The pharmaceutical and agrochemical uses are described. The uses in information recording are also discussed.