^a School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, Liaoning 110016, China 
^b Laboratory of Medicinal Chemistry, College of Pharmacy and Research Institute for Drug Development, Pusan National University, Busan 609-735, Korea 
^c College of Pharmacy, Seoul National University, Seoul 151-742, Korea 
^d Laboratory of Medicinal Chemistry, College of Pharmacy, Ewha Womans University, Seoul 120-750, Korea

Synthesis of north-5-methylbicyclo[3.1.0]hexyl purine and pyrimidine nucleosides with an ethynyl group at C-3 position has been successfully accomplished by a facile method. Methylbicyclo[3.1.0]hexanone (±)-5 having three contiguous chiral centers was remarkably simply constructed only by four steps containing a carbenoid insertion reaction in the presence of rhodium(II) acetate dimer and CuSO4, giving a correct relative stereochemistry of the generated three chiral centers. Upon Grignard reaction of (±)-5 with ethynylmagnesium bromide, exclusive diastereoselectivity was observed. Condensation of glycosyl donor (±)-9 with purine nucleobase afforded only the desired N9-alkylated nucleoside, while condensation with pyrimidine, N3-benzoylated uracil gave the desired N1-alkylated nucleoside (±)-13 with the undesired O2-alkylated nucleoside (±)-14. Probably, (±)-14 would be formed due to steric hindrance caused upon approaching for N1-alkylation.