Barium methoxide

Dihydroepistephamiersine 6-acetate (7) was isolated from Stephania abyssinica as a homogeneous oil. The UV spectrum showed an absorption maximum at 286 nm, and the IR spectrum exhibited a band corresponding to an aliphatic ester carbonyl group at 1725 cm-1 (20). The H-NMR data are summarized in Table II. In chemical investigations, hydrolysis of 7 with barium methoxide gave an alcohol identical with 6-dihydroepistephamiersine (17), which on further treatment with mineral acid gave the known alkaloid, stephasunoline (17). Thus structure 7 was proposed for 6-dihydroepistephamiersine 6-acetate (20). 

Khalique20 synthesized D-apiose by treating /ceto-D-fructose pen-taacetate (18) with diazomethane, and deacetylating the product (19) with barium methoxide to give epoxide (20), which, by oxidation with 2 equivalents of sodium metaperiodate, was converted into a syrupy epoxy-aldehyde (21), characterized as its crystalline phenylos-azone. Hydrolysis of compound 21 with aqueous acid produced... 

Because of this transformation, cardiac aglycons and cardenolides should not be exposed to alkalinity greater than that provided by aqueous bicarbonate solution. The use of the Zempl6n procedure88 for the saponification of O-acylated cardenolides is likewise hazardous, although Elderfield and coworkers12 18 were successful in deacetylating their synthetic cardenolides with barium methoxide in methanol. 

Di-O-mesyl-D-mannitol (46) can be converted under acidic conditions (Dowex 50W-X2 cation-exchange resin) by way of 1,4-anhydro-3-0-mesyl-D-talitol (47) into D-isoidide (49) in almost quantitative yield. On using triethylamine - water, 2,3 4,5-dianhydro-D-iditol (48) is formed from this, on treatment with an acid ion-exchanger, D-isoidide (49) is formed in only 20% yield (see Scheme 7). From these observations, it was decided5 7,98 that the 2,3 4,5-dianhydro isomer 48 cannot be an intermediate in the conversion of 46 into 49. Similar results were found for the reaction of 46 or 3,4-di-O-p-tolylsulfonyl-D-mannitol (p-CH3C6H4S02- instead of CH3S02-in 46) with barium methoxide in methanol.99... 

Shapiro and co-workers have described [89] (in a paper submitted just before the death of this pioneer in the field of glycosphingolipid synthesis — for a review of his extensive work in this area see Ref. [1]) a synthesis of the thio-analogue (88) of glucosyl ceramide (and the saturated derivative) from 2,3,4,6-tetra-0-acetyl-l-mercapto- 3-D-glucopyranose (86) and the 1-deoxy-l-iodoceramide derivative (85) in the presence of l,8-diazabicyclo[5.4.0]undec-7-ene. The product (87) was deacylated with methano-lic barium methoxide to give (88). 

All these substances reduce hot Fehling solution, though the anilide LXXIX required heating at 95° for two minutes. Treatment with 0.003 M barium methoxide in dry methanol at room temperature decomposed 3-keto-n-butyl 0-D-glucopyranoside tetraacetate (X), to yield D-glucose and methyl vinyl ketone (LXXX). 

The use of 2-deoxyribose derivatives tends to produce anomeric mixtures of nucleosides. Thus 3,5-di-0-p-nitrobenzoyl-2-deoxy-D-ribofuranosyl chloride and JV -benzoyladenine and molecular sieves gave, after deblocking with methanolic barium methoxide, a mixture of the anomeric 2 -deoxyadenosines (b-68MI40901, p. 183). A variation to this technique includes the condensation of JV -benzoylchloromercurioadenine with 5-0-benzoyl-2-deoxy-D-eryf/iro-pentose diisopropyl dithioacetal in acetonitrile under reflux over 4 hours to produce the same anomeric mixture of 2 -deoxyadenosines (B-68MI40901,p. 132). 

Deacetylatioii of the esters, which proceeds normally, has been siu cess-fully carried out with ammonia, sodium methoxide, or barium methoxide in methanol. In this way, for example, iV-p-tolyl-/8-D-glucosylamine 2,3,4,()-tetraacetate is converted into iV -p-tolyl-/8-D-gluoosylamine, and iV-acetyl-/8-D-galactosylamine tetraacetate into iV-acetyl-/8-D-galactosyl-amine. ... 

As a guide to the stability of epoxides, the procedure used for the deacetylation of the above glycosides is presented. The appropriate epoxypropyl glycoside was suspended in dry methanol (10% w/v) with rapid magnetic stirring, and treated with methanolic barium methoxide to give a final concentration of 0.02 M. After dissolution, precipitation of the 0-deacetylated products began within 5 min. After 12 hr at 3°C, the solids were collected, and crystallized from aqueous acetone. 

Barium methoxide, introduced by Weltzien and Singer, is often used in catalytic amounts as a somewhat milder alternative to sodium methoxide. As a convenient general procedure, the glycoside acetate (1 g.), dissolved or suspended in dry methanol (30-50 ml.) is treated with 0.4 N barium methoxide (1 ml.—prepared from the metal or the oxide), and left at 0° for about 24 hr. Barium may be converted into the sulfate at 0°, but the removal of colloidal barium sulfate may present difficulties hence, use of carbon dioxide was introduced. Barium methoxide has been particularly recommended for debenzoylation. ... 

Preparation (36). Cellulose in the form of cotton or filter paper is simultaneously acetylated and acetolyzed by the action of acetic anhydride and sulfuric acid at low temperatures. Cellobiose octaacetate crystallizes from the reaction mixture and after separation is recrystallized from alcohol. The acetyl groups are removed by any of several methods, preferably with barium methoxide in methanol solution. 

Compound (III), suspended in dry methanol (final concentration 10% w/v), is treated with methanolic barium methoxide solution to give a final concentration of 20 mM in base. After 12 hr at 4°, the reaction mixture is partly neutralized with a few chips of solid CO2 and evaporated to dryness. The residue is triturated with methanol and filtered, and dioxane is added dropwise to the filtrate until a permanent tiirbidity obtains. Compound (IV) crystallizes as needles. Yield, 60% m.p., 175°-178° , -37.5° C = 2, H2O). 

Barium methoxide, but not sodium or potassium methoxide, rearranges epoxyl-athrol (260) and related compounds to (283). 

---