Naphthyl as a chiral auxiliary in an asymmetric 1,4-addition reaction
摘要:
Naphthyl 3,4,6-tri-O-methyl-beta-D-glucopyranoside, easily synthesized from tri-O-acetyl-D-glucal, has been applied as a chiral auxiliary in an asymmetric Michael addition to the 2-O-crotonate. A very high facial diastereoselection (>95%) was obtained. No diastereoselection was observed when 1,3,4,6-tetra-O-methyl-beta-D-glucopyranoside was used as the chiral auxiliary. A stereochemical model, taking into account steric shielding and pi-stacking effects, is proposed on the basis of the observed results. (C) 1997 Elsevier Science Ltd.
Tandem Epoxidation‐Alcoholysis or Epoxidation‐Hydrolysis of Glycals Catalyzed by Titanium(IV) Isopropoxide or Venturello’s Phosphotungstate Complex
作者:Pieter Levecque、David W. Gammon、Henok Hadgu Kinfe、Pierre Jacobs、Dirk De Vos、Bert Sels
DOI:10.1002/adsc.200800079
日期:2008.7.7
Venturello’sphosphotungstatecomplex and titanium(IV) isopropoxide [Ti(O-i-Pr)4] were successfully used as catalysts for the epoxidation-alcoholysis of glycals using hydrogen peroxide [H2O2]. Reaction substrates included a range of variously protected glycals and different alcohols were used as solvents. Ti(O-i-Pr)4 was only effective in methanol as solvent, but gave methyl glycosides in high yields
Venturello的磷钨酸盐络合物和异丙醇钛(IV)[Ti(O- i- Pr)4 ]已成功用作使用过氧化氢[H 2 O 2 ]的环氧乙烷缩合醇解的催化剂。反应底物包括各种受保护的糖基,不同的醇用作溶剂。钛(O- i- Pr)4仅在甲醇作为溶剂中有效,但以高收率和高选择性得到甲基糖苷。事实证明,Ventrollo复合物是一种用途广泛且高效的催化剂。除了在醇类溶剂中进行环氧化-醇解以外,它还显示了在双相条件下的活性,以允许长链醇的糖基化,并且在苄基化的葡糖的立体选择性二羟基化中非常有效。
Highly Diastereoselective 1,4-Addition of an Organocuprate to Methyl α-<scp>d</scp>-Gluco-, α-<scp>d</scp>-Manno-, or α-<scp>d</scp>-Galactopyranosides Tethering an α,β-Unsaturated Ester. Novel Asymmetric Access to β-C-Substituted Butanoic Acids
yields. Other organocuprates also serve as effective carbon nucleophiles for the 1,4-addition. Removal of the carbohydrate moiety from each adduct afforded a variety of beta-C-substituted butanoic esters in remarkable enantiomeric excess. The 1,4-addition of the same cuprate to some methyl alpha-D-manno- or alpha-D-galactopyranosidic substrates in which a crotonyl group was incorporated, each at 3-OH
The chemistry of glucal halohydrins: The effect of the halide on epoxide formation
作者:Cecilia H. Marzabadi、Christopher D. Spilling、Lisa M. Tyler
DOI:10.1016/s0040-4020(01)81332-6
日期:1994.1
Chlorohydrins, bromohydrins, and iodohydrins, formed by hydroxyhalogenation of tri-O-methyl glucal, undergo base induced cyclization to give glucal epoxides. The mechanism of the cyclization reaction was probed using 1H NMR and deuterium incorporation studies. Cyclization and in situ trapping with Cs2CO3 in MeOD gave deuterated methyl 3,4,6-tri-O-methyl-α-D-mannoside and methyl 3,4,6-tri-O-methyl-β-D-glucoside
由三-O-甲基葡糖基的羟基卤化作用形成的氯醇,溴代醇和碘代醇经碱诱导的环化反应生成葡糖基环氧化物。使用1 H NMR和氘掺入研究探索了环化反应的机理。Cs 2 CO 3的环化和原位捕集在MeOD中得到氘化的甲基3,4,6-三-O-甲基-α-D-甘露糖苷和甲基3,4,6-三-O-甲基-β-D-葡萄糖苷和不饱和醛。这些研究导致环氧化物形成的优化的立体选择性。葡萄糖溴醇与NaH或LiHMDS在THF中于5°C反应,生成β-环氧化物,甘露糖碘醇与KH和18-crown-6在甲苯中,于-70°C反应,生成α-环氧化物。通过与苯硫醇钠反应打开环氧化物,得到苯基3,4,6-三-O-甲基-1-硫代-α-D-甘露吡喃糖苷(单一异构体)和苯基3,4,6-三-O-苯基甲基-1-硫代-β-D-吡喃葡萄糖苷(18:1)。
Gas-liquid chromatography-mass spectrometry of methylated and deuteriomethylated per-O-acetyl-aldononitriles from D-mannose
作者:Fred R. Seymour、Ronald D. Plattner、Morey E. Slodki
DOI:10.1016/s0008-6215(00)84162-2
日期:1975.11
D-mannopyranose were separated by gas-liquidchromatography, and analyzed by mass spectrometry. Through introduction of deuteriomethyl ether groups, various fragmentions constituting the mass spectra were identified and related to the parent methylated sugar structures. Also identified were several characteristic series of fragment ions that are common to two or more methylated D-mannopyranosides. As expected