There is a great deal of interest in developing stable modified nucleic acids for application in diverse fields. Phosphate-modified DNA analogues, in which the phosphodiester group is replaced with a surrogate group, are attractive because of their high stability and resistance to nucleases. However, the scope of conventional solution or solid-phase DNA synthesis is limited for making DNA analogues with unnatural linkages. Other limitations associated with conventional synthesis include difficulty in making larger polymers, poor yield, incomplete reaction, and difficult purification. To circumvent these problems, a single-crystal-to-single-crystal (SCSC) synthesis of a 1,5-triazole-linked polymeric ssDNA analogue from a modified nucleoside through topochemical azide-alkyne cycloaddition (TAAC) is reported. This is the first solvent-free, catalyst-free synthesis of a DNA analogue that proceeds in quantitative yield and does not require any purification.
The generation of sulfonyl radicals from sulfonyl azides using visible light and a photoactive iridium complex in THF is described. This process was used to promote sulfonylative and azidosulfonylative cyclizations of enynes to give several classes of highly functionalized heterocycles. The use of THF as the solvent is critical for successful reactions. The proposed mechanism of radical initiation involves the photosensitized formation of a triplet sulfonyl nitrene, which abstracts a hydrogen atom from THF to give a tetrahydrofuran‐2‐yl radical, which then reacts with the sulfonyl azide to generate the sulfonyl radical.
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