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13.13.1.1.3.1.1 Addition of Azides to Alkynes

DOI: 10.1055/sos-SD-013-00626

Tomé, A. C.Science of Synthesis, (200413438.

The thermal 1,3-dipolar cycloaddition of azides to alkynes is often the method of choice for the synthesis of 1,2,3-triazoles since it gives directly the desired product. However, when unsymmetrical alkynes are used, mixtures of the two possible regioisomers are usually obtained. In general, addition to unsymmetrical alkynes tends to give mainly the isomers with the electron-withdrawing groups at the 4-position and the electron-releasing groups at 5-position.[‌3‌] The low regioselectivity of these reactions is the major disadvantage of this method as a preparative procedure. The accepted mechanism for these reactions is a concerted 1,3-dipolar cycloaddition. Kinetic data and the regio- and stereoselectivity of these reactions strongly support this mechanism. However, the reactions involving ionic azides (e.g., sodium azide) follow a nonconcerted ionic mechanism. These mechanisms have been discussed and documented in reviews.[‌76‌,‌77‌]

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