Substituent Dependence of the Diastereofacial Selectivity in Iodination and Bromination of Glycals and Related Cyclic Enol Ethers
作者:Antonella Boschi、Cinzia Chiappe、Antonietta De Rubertis、Marie Françoise Ruasse
DOI:10.1021/jo000799x
日期:2000.12.1
azide trapping of any cationic intermediate, it is concluded that these brominations which do not go through an ionic intermediate are concerted additions of bromine and methanol with very loose rate- and product-determining transition states. Finally, the substituent conformation at C-4 influences drastically the stereoselectivity in all these brominations. Evidence for alpha-anomeric control of the
An efficient and benign method for the regio- and stereoselective synthesis of halohydrins and β-halo ethers from dihydropyrans, dihydrofurans and anhydro sugars in the presence of a halide salt and hydrogen peroxide is presented with tungstate-exchanged takovite as oxidation catalyst.
Synthesis of 6-Hydroxy-L-Daunosamine and L-Daunosamine Derivatives
作者:Laurent Daley、Pierre Roger、Claude Monneret
DOI:10.1080/07328309708006508
日期:1997.1.1
Methyl 3-trifluoroacetamido-2,3-dideoxy-alpha-L-lyxo-hexopyranoside (19) has been synthesized from D-glucose derivatives following two pathways. The first one involving 1,2:5,6-di-O-isopropylidene-alpha-D-glucopyranose as starting material is mainly based upon azidation at C-3, inversion of configuration at C-5 and then radical deoxygenation at C-2 (13 steps and 10% overall yield). This pathway also afforded methyl N-trifluoroacetyl-alpha-L-daunosamine 22. The second pathway, which started from tri-O-acetyl-D-glucal, relied essentially upon Michael addition of N3H on the corresponding hex-2-enose and glycosidation of the two pivaloyl compounds 33 and 34. After the beta-D-ribo isomer 34 was subsequently converted into its beta-methyl glycoside 28b, inversion of configuration at C-5 was carried out via the formation of the 6-bromo-sugar 36, followed by formation of the hex-5-enopyranoside 37. Hydroboration of 37 stereoselectively afforded 38, followed by catalytic hydrogenation and trifluoroacetylation to give 19.
Nakamura et al., Chemical and pharmaceutical bulletin, 1964, vol. 12, p. 1302,1306
作者:Nakamura et al.
DOI:——
日期:——
A convenient synthesis of 2-deoxy-d-arabino-hexose and of its methyl and benzyl glycosides