The acetonation of d-allose

Carbohydrate cyclic acetal formation and migration

“…Similar results were ob-tained60 on the benzylldenation of the nucleosides, adenosine, guanosine, cytidine, and uridine. Thus reaction at 0 °C gave the diastereomer with the phenyl group endo (216), and reaction at 100 °C gave an approximately equimolar mixture of the two diastereomers 216 and 217. Again 216 is the product of kinetic control and at elevated temperatures equilibration occurs with formation of the thermodynamically most stable Isomer.…”

5-Thiopyranoses. Part 11. Isopropylidene acetals of 5-thio-D-glucose, 5-thio-D-allose, and 5-thio-D-altrose and some of their methyl glycosides

“…Evaporation of the dried organic extract and crystallisation of the residue from light petroleum gave the diacetal(l4) (24 mg, 62%), m.p. 99-101 "C, (17). A solution of the sulphonate (17) (50 mg) in acetone (1 ml) containing toluene-p-sulphonic acid (10 mg) was kept at 20 "C for 5 days.…”

“…5-Thio-~glucose (9) thus differs from 5-thio-~-ribose and 5-thio-~xylose, where the pyranoid diacetals (1) and (2) were both kinetic and thermodynamic products, in that the pyranose diacetal (lla) is the product obtained under kinetic reaction conditions but the furanose diacetal(l0) is the thermodynamic product. The same considerations apply to the sulphonate esters (17) and ( 22), and (20) and (24).…”

“…In view of the existence'0-'' of 4,6-0alk ylidene-1,2-O-isopropylidene-a-~-glucopyranoses this was thought to be the 1,2:4,6-diacetal (14) and this was shown to be so by an independent synthesis of the diacetal (18). Methanolic sodium methoxide cleaved the sulphonate group of (17) to give the required diacetal(l4). A similar series of reactions starting from either of the methanesulphonates (19) or (20) and proceding via syrupy 3-O-methylsulphonyl-5-thio-~-glucose (21) and its diacetal(22) also led to compound (14).…”

A rationalization on the relative thermodynamic stabilities of fused five-membered tetrahydrofurans with epimerizable substituents. An anomeric effect in furanoses

“…(9) The product was not Investigated, but the presence of strong "cyano enamine" absorption In the infrared region (at 2180 and 1630 cm-1) supported the formation of 2-(1-piperidino)acrylonitrlle. (10) J. Ficini and A. M. Tonzin, Bull. Soc.…”