Previously, our group has developed a stereoselective construction of heterocyclic compounds using the Pd(II) catalyzed cyclization. We described here the applicaton of this methodology to synthesis of D-ribose, L-lyxose and spiro C-arylated glycoribosides (16). 1. Synthesis of D-ribose and L-lyxose The aldehyde 5 was prepared from cis-2-butene-1,4-diol (8) in 13 steps. By the reaction of hemiacetal derived from the aldehyde 5 and MeOH in the presence of 5 mol% of PdCl_2(PhCN)_2 in THF, the cyclized product 4 was obtained in 65% yield as diastereomer mixtures. D-ribose and L-lyxose were synthesized from the cyclized product 4A and 4B in 5 steps, respectively. 2. Synthesis of spiro C-arylated glycoriboside Spiro C-arylated glycopyranosides such as papulacandins 15 show many excellent activities. But there has been no report on the bioactivities of the spirocyclic ribose analogues. Thus we tried to synthesize the spiro C-arylated glycoriboside analogues 16 using Pd(II) catalyzed cyclization. The cyclized precursor 20 was prepared from the alcohol 12 in 3 steps. The key cyclization of 20 was achieved successfully by treatment with 20 mol% of PdCl_2(PhCN)_2 in THF to give the spiro compound 17. Finally, the glycoriboside analogue 16 was syntehsized from 17 in 5 steps.
