Pyranosides—

Photoannulation of ethylene or vinyl acetate to enone (161) gave mixtures of diastereomers (178) and (179) respectively, which were not well resolved by column chromatography. However further transformations 

---

Linamarin, acetonecyanhydrin, -D>gluco-pyranoside, CeH, 0j 0 C CH3)2 CN. M.p. I43-I45°C. Present in young flax plants and in Phaseolus lunatus and is also the glycoside of rubber seeds. Such glycosides may be regarded as primary materials for synthesis. 

Write structural formulas for the a and 3 methyl pyranosides formed by reaction of o galactose with methanol in the presence of hydrogen chloride... 

PhN=C=0, Pyr, 20°, 2-3 h, 100% yield. This method was used to protect selectively the primary hydroxyl group in several pyranosides. ... 

With this ortho ester good selectivity for the axial alcohol is achieved in the acidic hydrolysis of a pyranoside derivative." ... 

Neighbouring diaxial protons of cyclohexane can be clearly identified by their large coupling constants 11-13 Hz, Table 2.10) which contrast with those of protons in diequatorial or axial-equatorial configurations ( Jee 2-4 Hz). Similar relationships hold for pyranosides as oxy-... 

Cyclic sulfates rapidly react with the fluoride ion sources to give monofluoro derivatives Thus, the 2,3-cyclic sulfate of methyl-4 6 O benzylidene p D manno pyranoside cleanly reacts with tetramethylammonium fluoride to give methyl 4,6-0-benzylidene 2 deoxy 2 fluoro-p-D-glucopyranoside-3-sulfate Acid hydrolysis followed by acetylation gives 2 deoxy 2 fluoro-P-D-glucopyranoside triacetate in 84% isolated yield [5S] (equation 38)... 

This ether, developed for the protection of a pyranoside anomeric hydroxyl, is prepared via a Konigs-Knorr reaction from the glycosyl bromide and 2-(ben-zylthio)ethanol in the presence of DIPEA. It is cleaved, after oxidation with dimethyldioxirane, by treatment with LDA or MeONa. ... 

The /7-nitrophenyl ether was used for the protection of the anomeric position of a pyranoside. It is installed using the Konigs-Knorr process and can be cleaved by hydrogenolysis (Pd/C, H2, AC2O), followed by oxidation with ceric ammonium nitrate (81-99% yield). ... 

HCOOH, 60°, 1 h, 93% yield. This method can be used to protect selectively only the primary alcohol of a pyranoside. ... 

Bu2SnO, toluene, reflux, 4 h Pd(Ph3P)4, THE, CH2=CHCH(OAc)2, rt, 1 h, 80-89% yield. In pyranoside protection, selectivity for 1,3-dioxane formation is generally observed, but dioxolanes are often formed. 

In addition, NaOMe, and NaNH2, have also been employed. Applieation of phase-transfer conditions with tetra-n-butylammonium iodide showed marked improvement for the epoxide formation. Furthermore, many complex substituted sulfur ylides have been synthesized and utilized. For instance, stabilized ylide 20 was prepared and treated with a-D-a/lo-pyranoside 19 to furnish a-D-cyclopropanyl-pyranoside 21. Other examples of substituted sulfur ylides include 22-25, among which aminosulfoxonium ylide 25, sometimes known as Johnson s ylide, belongs to another category. The aminosulfoxonium ylides possess the configurational stability and thermal stability not enjoyed by the sulfonium and sulfoxonium ylides, thereby are more suitable for asymmetric synthesis. 

Mosher and coworkers have adopted this strategy for the enandoselecdve synthesis of 2,3-thdeoxy-3-nitro-furanosides and pyranosides using chirM nitronate dianions, as shown in Eq. 5.5."... 

From the evidence discussed above, the framework of methylkasugaminide is determined to be methyl 2,4-diamino-2,3,4,6-tetradeoxyhexo-pyranoside in which hydrogens at C-4 and C-5 are axial-axial and hydrogens at C-l and C-2 are not in axial-axial relation. The structure was definitely proved by the application of the spin decoupling technique and, moreover, the relative relations of all hydrogens were confirmed. 

By monitoring the intensity of the carbonyl absorption it was observed that oxidation of methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexopyrano-side with chromium trioxide-pyridine at room temperature gave initially the hexopyranosid-3-ulose (2) in low concentration, but attempts to increase this yield resulted in elimination of methanol to give compound 3. However, when methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexo-pyranoside is oxidized by ruthenium tetroxide in either carbon tetrachloride or methylene dichloride it affords compound 2 without concomitant elimination. When compound 2 was heated for 30 minutes in pyridine which was 0.1 M in either perchloric acid or hydrochloric acid it afforded compound 3, but in pyridine alone it was recoverable unchanged (2). Another example of this type of elimination, leading to the introduction of unsaturation into a glycopyranoid ring, was observed... 

No quantitative data were available on the reactivity at C-4 in hexose sulfonates until the studies of Stevens and co-workers (95). It was shown that when methyl 6-deoxy-2,3-di-0-benzyl-4-0-methylsulfonyl-a-D-gluco-pyranoside (31) was allowed to react with sodium iodide in pentane-... 

Treatment of methyl 2-azido-4,6-0-benzylidene-2-deoxy-a-D-altro-pyranoside (128) (42) with 121 followed by refluxing and processing afforded a chloro derivative as a sirup in 70% yield (46, 49). Reduction of this product with an excess of Raney-nickel in methanol containing acetic anhydride afforded a crystalline product, m.p. 179°C., which is formulated as the d-manno analog 131. The actual product is most likely methyl azido-4,6-0-benzylidene-3-chloro-2,3-dideodxy - a - d - mannopyran-oside (130) resulting from attack of chloride ion at C-3 with inversion of configuration in the intermediate 129. Had the chlorination proceeded... 

Figure 2. Mass spectrum of methyl 4-deoxy-fi-T>-t xeo-pento-pyranoside (5).

W-Methylation of Methyl 2-Acetamido-2-deoxy-a-D-gluco-pyranoside, S. A. Barker, M. Stacey, and D. J. Tipper, Nature, 184 (1959) 1718. 

---