Z ah id a M aq b o o l+-a, M ashooda H asan 3, Kevin T. Pott a, A bdul M alik++ C, T anveer A h m ad N izam ic, W olfgang V o elter* c A convenient pathway to a variety of ß-and a-C-nucleosides has been developed by utiliz ing 1,3-dipolar cycloaddition reactions of various exocyclic and endocyclic heterocyclic ylides with ß (5a) and a (5b) anomers of ethyl 3-(2',3'-0-isopropylidene-5'-0-trityl-D-ribofuranosyl) propiolate, respectively. Assignment of configuration at exposition of the C-nucleosides could be made by a comparative study of the properties of corresponding a and ß anomers with a reasonable degree of certainity.

C-Nucleosides, 1,3-Dipolar Cycloaddition 1,3-Dipolar cycloaddition of dipolarophiles (1) and (2) with endocyclic heterocyclic azomethine ylides (4), (14) and (24), prepared in situ, leads to the protected ß-and a-C-nucleosides (7), (8), (17), (18), (27) and (28), respectively. These, on subsequent hydrolysis, provide the corresponding C-nucleosides. The structures o f all the synthesized com pounds are con firmed through analytical and spectral data. The assignment of configuration at C -l' position of the C-nucleosides could be done by a comparative study of the properties of the corre sponding a and ß anomers with a reasonable degree of certainity. * Reprints requests to Prof. Dr. W. Voelter. + Present address: Senior Scientific Officer, PINS-TEC H , Islamabad. Pakistan. ++ On leave from H. E. J. Research Institute of Chemis try, University of Karachi, Karachi-75270, Pakistan.

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