First synthesis of both 1-aryl-4-[(E)-alk-1-enyl]-1H-1,2,3-triazoles and 1-aryl-4-[(Z)-1-(trimethylsilyl)alk-1-enyl]-1H-1,2,3-triazoles: assembly of π-extended 1,2,3-triazoles using a cross-coupling/click reaction sequence

A practical and general synthetic approach to a series of π-extended 1,2,3-triazoles with both aryl and alkenyl moieties on the triazole ring is described. Synthesis of 1-aryl-4-[(E)-alk-1-enyl]-1H-1,2,3-triazoles can be achieved by the click reaction between terminal conjugated (E)-enynes, prepared by copper-mediated cross-coupling reaction of (E)-alk-1-enyldisiamylboranes with (trimethylsilyl)ethynyl bromide, and aryl azides, prepared from arylboronic acids and sodium azide in another flask and employed for the following click reaction without any purification. 1-Aryl-4-[(Z)-1-(trimethylsilyl)alk-1-enyl]-1H-1,2,3-triazoles can be also synthesized by a sequential three-step reaction, which involves copper-mediated cross-coupling reaction of (Z)-1-(trimethylsilyl)alk-1-enyldicyclohexylboranes with (trimethylsilyl)ethynyl bromide to form (Z)-1,3-bis(trimethylsilyl)alk-3-en-1-ynes, deprotection of the trimethylsilyl group on the alkynyl carbon atom to generate (Z)-3-(trimethylsilyl)alk-3-en-1-ynes and click reaction with aryl azides prepared in the same manner as described above. Both synthetic routes are tolerant of a wide range of functional groups with moderate to good yields.

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