Condensation of triphenylphosphinemethylene (Wittig reagent) with 5-0-benzyl-1,2-0-isopropylidene-a-D-erythro-pentafuranos-3-uloe and with 1,2:5,6-di-O-isopropylidene-a-~-ribo-hexofuranos-3-ulose (1) afforded 5-O-benzyl-l,2-O-isopropylidene-3-deoxy-3-C-methylene-a-~-ribofuranose in 36% yield and 1,2:5,6-di-O-isopropylidene-3-C-methylene-a-~-ribo-hexofuranose (2) in 55% yield, respectively. A detailed study of the affect of reaction conditions on the yield of the unsaturated sugar is described. Hydrogenation of 2 proceeded stereoselectively to yield 4 which was hydrolyzed selectively to the 1,2-0-monoisopropylidene derivative 5. Benzoylation of the latter gave 6 which was converted by acetolysis to the 1,2-diacetate 7. Condensation of this compound with 6-benzamidochIoromercuripurine in the presence of titanium tetrachloride followed by deblocking with methanolic sodium methoxide, yielded 9-(3-deoxy-3-C-methyl-8-D-allofuranosy1)adenine (10) in 48 % yield based o n 7. Sodium metaperiodate oxidation of 10, followed by sodium borohydride reduction of the aldel~ydo derivative, afforded 9-(3-deoxy-3-C-methyl-p-D-ribofuranosy1)adenine (11) in 85 % yield.Canadian Journal of Chemistry, 47, 3941 (1969) Interest in 3'-deoxyribofuranosyl nucleosides stems partly from the fact that 3'-deoxyadenosine (cordycepin, the first isolated nucleoside antibiotic) inhibits nucleic acid synthesis in Ehrlich ascites cells (1,2). The recent synthesis of 3'-Cmethyladenosine (3) and the finding that it also exhibits biological activity, has further stimulated a concern in the nucleoside antibotics. Branchedchain sugar nucleosides have recently been prepared from 3-deoxy-3-C-hydroxymethyl-D-erythrofuranose (4). Our laboratory has been interested in developing a gensral method of synthesis of branched-chain sugar nucleosides (5), and in particular, the synthesis of 3'-deoxy and 2'-deoxy branched-chain sugar nucleosides having the ribofuranosyl skeleton in the sugar moiety. In this paper we wish to report the synthesis of several deoxy branched-chain sugar nucleosides and in particular, the synthesis of a structural analogue of cordycepin by application of a Wittig reaction to ketoses.The readily available 1,2:5,6-di-0-isopropylidene-a-D-ribo-hexafuranos-3-ulose (1) (6,7) is a useful intermediate for the synthesis of 3-deoxy-3-C-substituted branched-chain sugars. In a previous communication (8) we described the application of the modified Wittig reaction to 1 to afford a 3-hydroxyethyl substituted branchedchain sugar, and in this paper we report the application of the basic Wittig reaction to the ketose 1. Condensation of triphenylphosphinemethy-'For papers I and 11 see references 20 and 21. lene with 1 in the ratio 3 :1 using methyl sulfoxide as solvent (9,lO) gave 1,2:5,6-di-0-isopropylidene-3-C-methylene-a-D-ribo-hexofuranose (2) in 55% yield, and in addition, a by-product 3 of unknown constitution. Compounds 2 and 3 were separated by column chromatography on silica gel. The yield of 2, as shown in Table I, was dependent on the reacti...