Efficient synthesis of organosoluble 6-azido-6-deoxy-2,3-O-trimethylsilyl cellulose for click reactions

Huisgen cycloaddition has proven to be a powerful tool for the derivatization of cellulose, but the choice of reaction partners is limited by the solubility of the cellulose derivative. In this report, we show the efficient synthesis of an azide-bearing, organosoluble cellulose derivative via the 6-bromo-6-deoxy-2,3-O-trimethylsilyl cellulose (Br-TMSC) obtained through a novel one-pot reaction. It opens the possibility to perform the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) under moisture free conditions. First, the one-pot approach was used to synthesize Br-TMSC by combining homogeneous and regioselective bromination at C-6 position and silylation at C-2/C-3 positions. Then, 6-azido-6-deoxy-2,3-O-trimethylsilyl cellulose (N₃-TMSC) as the starting material for the CuAAC was obtained via nucleophilic substitution of the bromine by azide moiety. Furthermore, N₃-TMSC was exemplarily reacted with phenylacetylene and 3-cyclopentyl-1-propyne in the CuAAC in dry tetrahydrofuran (THF) as solvent and showed nearly complete conversion of the azide functionality. All products have been characterized by FTIR spectroscopy, NMR spectroscopy, elemental analysis and gel permeation chromatography (GPC).