Application of Hantzsch Dihydropyridine in Copper-Catalyzed [3 + 2] Cycloaddition of Terminal Alkynes with Azides.

2,6-Dimethyl-3,5-bis(ethoxycarbonyl)-1,4-dihydropyridine (dihydropyridine Hantzsch ester, DHPHE) and CuSO4 · 5H2O efficiently accelerated azide–alkyne cycloaddition reactions of both aliphatic and aromatic substrates and gave 1,4-disubstituted 1,2,3-triazoles as the only isomer in good to excellent yields at room temperature with 1 mol% of CuSO4 · 5H2O/DHPHE (1:1 in molar ratio). The reaction could be carried out smoothly in methanol in air with high efficiency. DHPHE may play multiple important roles in the reaction: a reducing reagent to generate the catalytic center copper(I) from CuSO4, a base to help form the intermediate acetylide, and a ligand to stabilize the catalytic copper(I) species via coordination after being transformed to pyridine derivative. [Supplementary materials are available for this article. Go to the publisher's online edition ofSynthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] [ABSTRACT FROM AUTHOR]