Improved protocols for microwave-assisted Cu(I)-catalyzed Huisgen 1,3-dipolar cycloadditions

The Huisgen 1,3-dipolar cycloaddition of azides and acetylenes catalyzed by Cu( I) salts, leading to 1,2,3-triazoles, is one of the most versatile click reactions. We have developed a series of optimized protocols and new applications of this reaction starting from several substrates, comparing heterogeneous vs homogeneous catalysis, conventional heating vs microwave irradiation or simultaneous microwave/ultrasound irradiation. Both non-conventional techniques strongly promoted the cycloaddition ( bromide. azide. triazole), that could be conveniently performed in a one-pot procedure. This was feasible even with such bulky molecules as functionalized beta-cyclodextrins ( beta-CD), starting from 6(1)-O-tosyl-beta-CD or from heptakis[ 6-O-(tert-butyldimethylsilyl)]-2(1)-O-propargyl-beta-CD. Greener heterogeneous catalysis with charcoal-supported Cu( II) or Cu( I) ( prepared under ultrasound) was advantageously employed.