1,3-Dipolar cycloaddition approach to pyrrolidine analogues of C-nucleosides related to pseudouridine

Pyrrolidine analogues of C-nucleosides related to pseudouridine have been synthesized by 1,3-dipolar cycloaddition reactions of uracil-5 and 2,4-dimethoxypyrimidine-5 nitrones with allyl alcohol and methyl acrylate, and subsequent reductive cleavage of the isoxazolidine cycloadducts. The dimethoxy derivatives have been easily deprotected to the corresponding uracils bearing the pyrrolidine ring instead of a sugar moiety. The regio and stereoselectivity of the reactions are discussed.