One-Pot Synthesis of 1,2,3-Triazoles from Benzyl and Alkyl Halides, Sodium Azide and Alkynes in Water Under Transition-Metal-Catalyst Free Reaction Conditions

In the absence of any catalysts and additives, one-pot synthesis of 1,2,3-triazoles from benzyl and alkyl halides, sodium azide and alkynes in water was developed. The reactions of terminal arylalkynes, sodium azide with benzyl chlorides and bromides generated the corresponding regiospecific 1,4-disubstituted triazoles in excellent yields, but terminal aliphatic alkynes afforded the mixture of regioisomers (1,4- disubstituted and 1,5-disubstituted triazoles). For the reactions of primary aliphatic bromides, sodium azide and phenylacetylene, the ratio of 1,4- to 1,5-isomers ranging from 57 : 43 to 100 : 0 indicated 1,4- disubstituted regioselectivity of the reaction was raised with the increase of the carbon chain in primary aliphatic bromides. The present procedure does not require isolation of the azide intermediates and may prove to be especially useful when unstable low-molecular weight and polyvalent azides are needed. Furthermore, it is an ideal environmental benign reaction system only using water as solvent without any catalysts and additives.