A novel approach to the synthesis of purine nucleoside analogues, featuring the reaction of the C6-N1-O- aldonitrone moiety of 9-ribosyl-purine (nebularine) N1-oxide with some representative dipolarophiles, as well as Grignard reagents, is reported. Addition of Grignard reagents to the electrophilic C-6 carbon of the substrate allows a facile access to C-6 C-substituted purine nucleosides without using metal catalysts. 1,3- Dipolar cycloaddition processes lead to novel nucleoside analogues via opening, degradation or ring- enlargement of the pyrimidine ring of the base system of the first-formed isoxazoline or isoxazolidine cycloadduct.