REGIOSELECTIVE AND REGIOSPECIFIC CYCLOADDITION OF ACETYLENES TO 2,4,6-TRIAZIDOPYRIDINE

Abstract

The cycloaddition of tert-butylacetylene to 2,4,6-triazido-3,5-dicyanopyridine and 2,4,6-triazido-3-chloro-5-cyanopyridine occurs regioselectively and regiospecifically at the azide group in position 4 of the pyridine ring leading to the formation of the corresponding 4-(4'-tert-butyl-1H-1,2,3-triazolyl)pyridines as the sole products. Analogous reactions with the less sterically hindered n-butylacetylene are characterized by less regiospecificity and give a mixture of the isomeric 4'- and 5'-n-butyl-substituted triazoles at ratios of 96:4 and 91:9 respectively for the two different triazides. The interaction energies of the pyridine γ‑ and γ-azide groups with the acetylene molecules, and the energies of the transition states for these reactions have been calculated by the PM3 method. It was established that the high reactivity of the γ‑azide group of the triazidopyridines in relation to the acetylenes is caused by the anomalously low distribution of bonding orbital density on these groups, leading to substantially lower activation energies in 1,3-dipolar cycloaddition reactions.

Author: S. V. Chapyshev.

English Translation in Chemistry of Heterocyclic Compounds, 2000, 36 (11), pp 1289-1299

http://link.springer.com/article/10.1023/A%3A1017519401153