Highly stereoselective C-α-d-ribofuranosylation. Reactions of d-ribofuranosyl fluoride derivatives with enol trimethylsilyl ethers and with allyltrimethylsilane

Abstract

2,3,5-Tri-O-methyl-d-ribofuranosyl flouride (6), 2,3-di-O-benzyl-5-O-methyl-d-ribofuranosyl fluoride (7), and 5-O-benzyl-2,3-di-O-methyl-d-ribofuranosyl fluoride (8) were obtained in 57 (6α, 15; and 6β, 42), 87 (7α, 22; and 7β, 65), and 85.5 (8α, 35.5; and 8β, 50%) yields, respectively, from the corresponding OH-1 derivatives by the reaction with N,N-diethyl-1,1,2,3,3,3-hexafluoropropylamine, adduct of hexafluoropropene with diethylamine. These fluorides and 2,3,5-tri-O-benzyl-d-ribofuranosyl fluoride (5) reacted with isopropenyl trimethylsilyl ether, (Z)-1-ethyl-1-propenyl trimethylsilyl ether, and allyltrimethylsilane, in the presence of boron trifluoride·diethyl etherate to give the corresponding 1-d-ribofuranosyl-2-propanones, 2-d-ribofuranosyl-3-pentanones, and 3-d-ribofuranosyl-1-propenes in good yields. C-Acetonylation was confirmed to afford the α-d anomer as the initial product, and the α-d anomer was isomerized into the corresponding β-d anomer to give a mixture. The C-allylation reaction gave only the α-d anomer. C-Pentanonylation, however, gave a mixture of diastereoisomers that could not be isolated. All reactions afforded almost the same results starting with either α- or β-d-ribofuranosyl fluoride. No reaction of the β anomer of 5 with 1-isopropyl-2-methyl-1-propenyl trimethylsilyl ether took place. © 1987.