Click Chemistry for the Synthesis of Dihydrotriazoles

The activation enthalpies for the cycloaddition of alkynes and alkenes are similar however, since triazoles are more stable (30-40kcal/mol) than dihydrotriazole products, the cycloaddition is very exothermic and therefore irreversible. 

Honk et studied substituent effects in the 1,3-dipolar cycloaddition of azides with alkenes and alkynes on the basis of reactant concentrations, in order to explore the equilibrium constant and examine the reversibility or irreversibility of these reactions. They affirmed a lower barrier for the cycloaddition between electron-deficient azides such as 

In 1987, Buchanan et al. published a new route to chiral hydroxypyrroMines via intramolecular 1,3-cycloaddition starting from 2,3-0-isopropylidene-D-erythrose. They confirmed that dihydrotriazoles act as a stable intermediate after the cycloaddition of the azide derivative, but only in the case of the f -isomer. However, the analytical data of the resulting diazo ester, based on both isomers (E- and Z-isomer), was similar after treatment with sodium ethoxide. 

In the field of dihydrotriazoles, some results were previously published by Quasi et al. on the photoextrusion of nitrogen out of dihydrotriazole as well as dihydrotetrazole derivatives. Their dihydrotriazole synthesis was based on Trost s and Pearson s 1,3-dipolar cycloaddition from the lithium enolate of methylisobutyrate with alkyl azides at a lower temperature (-78°C). ° 

9 Cycloaddition Reactions with Azides to Give Thiatriazoles 

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