Anti Regiospecificity in the Photosensitized Cycloaddition of 4‐Tetrazolouracil Nucleoside^†

Abstract

The [2 + 2] photocycloaddition of natural pyrimidine nucleobases is devoid of regioselectivity. Although modified pyrimidines have been developed to selectively obtain syncyclobutane isomers, the targeted formation of anticyclobutane isomers has not been addressed yet. Herein, using NMR analyses and DFT calculations, we demonstrate that the acetone photosensitized excitation of the 4tetrazolouracil motif in the nucleoside series specifically provides anti-cyclobutane photoproducts in 51% yield. In addition, the cis stereomer formation is preferred over the transcyclobutane formation (71:29).