Chromium methoxide

The physical properties of samples of Cr(OMe)3 prepared by a variety of methods have been investigated.736 Good crystals could not be obtained but limited crystallography suggested a layered lattice with chromium occupying octahedral sites. A useful summary of earliei preparations and attempted preparations of chromium methoxides can be found in this paper. 

A lanthanum-chromium methoxide complex was prepared by Bilger et al. (1997) for the synthesis of lanthanum chromite (LaCrOs) powder. The starting materials for the two cations were lanthanum trichloride heptahydrale and chromium trichloride hexahydrate. The methoxide complex was hydrolyzed, and the product peptized to obtain a stable sol. Calcined gel particles gave rise to stoichiometric LaCrOa powders (see also Mechanical Dispersion of Sols ). 

We shall describe a specific synthetic example for each protective group given above. Regiosdective proteaion is generally only possible if there are hydroxyl groups of different sterical hindrance (prim < sec < tert equatorial < axial). Acetylation has usually been effected with acetic anhydride. The acetylation of less reactive hydroxyl groups is catalyzed by DMAP (see p.l44f.). Acetates are stable toward oxidation with chromium trioxide in pyridine and have been used, for example, for protection of steroids (H.J.E. Loewenthal, 1959), carbohydrates (M.L. Wolfrom, 1963 J.M. Williams, 1967), and nucleosides (A.M. Micbelson, 1963). The most common deacetylation procedures are ammonolysis with NH in CH OH and methanolysis with KjCO, or sodium methoxide. 

Bis(2,4-pentanedionato)chromium, 3326 Molybdenum hexamethoxide, 2596 Potassium /er/-butoxide, 1650 Potassium ethoxide, 0861 Potassium methoxide, 0450... 

The 774-vinylketene complex (85) could be oxidatively decomplexed with Ce(IV) to afford the lactone (87). Although no reaction was observed with methanol (unlike a postulated chromium analogue16,18 26), treatment with sodium methoxide produced the expected /3, y-unsaturated ester (88). Thermolysis of complex 85 afforded no trace of the naphthol that one would expect33 from a proposed chromium vinylketene complex with the same syn relationship between the phenyl group and the ketene moiety. Instead, only the furan (89.a) was seen. Indeed, upon exhaustive reaction of tricarbon-ylcobalt carbenes (84 and 90) with different alkynes, the furans (89.a-d) were isolated as the exclusive products in moderate to excellent yields. 

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

Peroxyacids oxidize the imine group in (236) and related compounds to the nitrone. The 1,4-benzodiazepine (178) and its 4,5-dihydro analogue can be oxidized to the 2-oxo derivatives with chromium(VI) oxide. The benzodiazepinone (236) can be hydroxylated at the 3-position via a two-step process firstly reaction with LTA gives the 3-acetoxy derivative and this can then be hydrolyzed in high yield using sodium methoxide in methanol/methylene chloride. The 3-acetoxy derivative may also be prepared via bromina-tion with NBS and reaction with sodium acetate in situ (79JHC1449). 

In the case of the tricarbonylarene metals, enhancement of nucleophilic substitution relative to the free arene is reported 106), In contrast to earlier reports 106) Friedel-Crafts acylation of tricarbonylbenzene chromium occurs under mild conditions 18), Molecular-orbital calculations of the 7r-electron activation energies for these reactions 63) confirm enhanced nucleophilic reactivity and suggest electrophilic activity similar to that of the free arene. The nucleophilic displacement of halide by methoxide ion... 

Oxidation of 172 with chromium trioxide in pyridine gave the monoketone 176, whereas oxidation of spiradine F under the same conditions afforded the hydroxylactam 177. Catalytic hydrogenation of compound 176 afforded the a-ketol 178. The latter was treated with sodium methoxide in benzene to give an enolated a-diketone (179), which definitely fixed the position of the hydroxyl group at C-6 in spiradine G. Comparison of an ORD curve of compound 178 with that of 5a-cholestane-6-one established the indicated absolute configuration for these alkaloids. It is worth noting that these alkaloids bear many structural similarities to the earlier mentioned alkaloid ajaconine. 

A novel diacetal of L-xi/lo-3-hexulose has been isolated in the course of studies on a general method for the synthesis of 3-hexuloses by oxidation of fully acetylated, hexitol monoacetals with chromium trioxide. Oxidation of l,2,5,6-tetra-0-acetyl-3,4-0-methylene-D-glucitol with chromium trioxide in acetic acid yielded principally l,2,5,6-tetra-0-acetyl-4-0-formyl-D-nbo-3-hexulose. The material remaining in the mother liquors was saponified with sodium methoxide in methanol and the product treated with acetone containing concentrated sulfuric acid a di-O-isopropylidene derivative, presumably l,2 3,4-di-0-isopropylidene-j8-L-xj/lo-3-hexulofuranose (116), was obtained. 

The reflectance spectra of d chromium(m) methoxide and ethoxide " agreed with ligand field predictions for an octahedral d ion with 10 Dq 17 000 cm (Table 2.22). 

Tributyltin acetate, see Sn-00289 >Tributyltin chloride, see Sn-00252 >Tributyltin hydride, see Sn-00258 Tributyltin isocyanate, see Sn-00278 Tributyltin methoxide, see Sn-00279 Tributyltin methylthiolate, see Sn-00280 Tributylvinylstannane, Sn-00290 Tricarbonyl(7 -benzyltrimethylstannane)chromium, see Sn-00273... 

C3gHygCrO, Tetrakis[bis(t-butyl)methoxo]chromium(IV), 46B, 1161 C36Hio80ftuZr13, Zirconium oxide methoxide, 43B, 1379 C38H3gAs2Cl2Co03, Bis(triphenylarsine oxide)dichlorocobalt(II) -ethanol, 43B, 1380... 

The Woodward synthetic route was initiated with a Diels-Alder reaction between 1,4-benzoquinone (14) and diene 15. The cycloadduct 16 formed in this way underwent Meerwein-Pondorff-Verley reduction to afford tricyclic lactone 17 which was converted to bromoether 18. Treatment of this substance with methoxide gave the methyl ether 19. Conversion of 19 to its halohydrin followed by chromium oxidation provided the a-bromo ketone 20 which upon treatment with zinc in glacial acetic acid afforded the bicyclic enone 21. This substance was transformed to the aldehyde-acid 23 by an osmylation-periodate cleavage sequence. The acid function in 23 was es-terified and the aldehyde moiety was condensed with 6-methoxytryptamine. The Schiff base intermediate obtained in this fashion was reduced to give an amine which provided the lactam 24 upon intramolecular acylation. Bischler-Napieralski cyclization of 24 gave the pentacyclic intermediate 25 in which... 

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