Photochemical ring expansion of 4-azidouracil: a route to 5H-1,3,5-triazepin-2,4-dione in the nucleoside series |
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Authors: | Peyrane Frédéric Cesario Michèle Clivio Pascale |
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Institution: | Institut de Chimie des Substances Naturelles, UPR 2301 CNRS, 1 Avenue de la Terrasse, 91190 Gif-sur-Yvette, France. |
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Abstract: | Under aqueous conditions, 4-azidouracil/tetrazolo1,5-c]pyrimidin-5(6H)-one nucleosides undergo a very efficient photochemical nitrogen elimination and ring expansion to 1,3,5-triazepin-2,4-dione nucleosides whose structure has been confirmed by X-ray crystallography. In contrast, when the photolysis was attempted under anhydrous conditions in the presence of a nucleophile, a ring contraction reaction occurred, affording 2-oxoimidazolone nucleosides. A mechanism to account for the formation of ring expansion and contraction reactions and involving a carbodiimide intermediate is proposed which is reminiscent of the known photochemical behavior of 2-azidopyridines/tetrazolo1,5-a]pyridines. |
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