Pentamethyl ether

Ethers of benzenepentol have been obtained by Dakin oxidation of the appropriately substituted acetophenone. Thus, the oxidation of 2-hydroxy-3,4,6-ttimethoxyacetophenone and 2-hydroxy-3,4,5-ttimethoxyacetophenone with hydrogen peroxide ia the presence of alkali gives l,2-dihydroxy-3,4,6-ttimethoxybenzene and l,2-dihydroxy-3,4,5-ttimethoxybenzene, respectively further methylation of these ethers yields the pentamethyl ether of benzenepentol (mp 58—59 degC) (253). The one-step aromatization of myoinositol to produce esters of pentahydroxybenzene is achieved by treatment with carboxylic acid anhydrides ia DMSO and ia the presence of pyridine (254) (see Vitamins). 6-Alkyl- or... 

Quaternary ammonium compounds biocidal activity mechanism, 1, 401 toxicity, 1, 124 Quaternization heterocyclic compounds reviews, 1, 73 ( )-Quebrach amine synthesis, 1, 490 Queen substance synthesis, 1, 439 4, 777 Quercetin occurrence, 3, 878 pentamethyl ether photolysis, 3, 696 photooxidation, 3, 695 Quercetrin hydrolysis, 3, 878 Quinacetol sulfate as fungicide, 2, 514 Quinacridone, 2,9-dimethyl-, 1, 336 Quinacridone pigments, 1, 335-336 Quinacrine... 

Success finally resulted when the inosose ether (20) was converted to its ethylene mercaptal. The crude mercaptal was reduced with nickel, and the crude pentol pentamethyl ether cleaved in the usual manner. 

The tetramethyl ether (15) mentioned above was also converted to its equatorial monobenzoate (16), and the latter methylated and de-esterified to give a hexol pentamethyl ether. As benzoyl migration occurred during methylation, this pentamethyl ether had the configuration 18, and was not the diastereomer (19) mentioned above (27). 

In early experiments, the pentamethyl ether (18) was treated with phosphorus pentachloride in the hope of obtaining a chloropentol reducible to ( — )-proto-quercitol. (Allowing for the benzoyl migration, the expected product would have been (— )-uibo-quercitol (11).) Surprisingly, the quercitol actually obtained after demethylation and dehalogena-tion was neither of these but still another previously known isomer, meso-scyllo-quercitol (24) (27). 

Koenigs-Knorr reaction of, 990 molecular model of, 119, 126, 985 mutarotation of, 985-986 pentnacetyl ester of, 988 pentamethyl ether of, 988 pyranose form of, 984-985 pyruvate from. 1143-1150 reaction with acetic anhydride, 988 reaction with ATP, 1129 reaction with iodomethane, 988 sweetness of. 1005 Williamson ether synthesis with. 988... 

Kinoshita, T. and Firman, K., Myricetin 5,7,3, 4, 5 -pentamethyl ether and other methylated flavonoids from Murraya paniculata. Phytochemistry, 45, 179, 1997. 

Several flavonoids have given mixtures of products on irradiation for example, the 3-phenylflavone (380) in methanol is converted into the isocoumarins (381) and (382) the latter is the major product and is derived from the former (75CC241). Quercitin pentamethyl ether (383) in methanol and in the absence of oxygen yields four tetracyclic products. In deoxygenated benzene, the reaction rate is doubled but only (384) and (385) are formed. This photocyclization is not inhibited by triplet quenchers and the primary photointermediate is in the triplet state (67JA6213). 

The irradiation of quercetin pentamethyl ether (392) in methanol leads to the formation of four products 405 the two principal products have been named lumimethylquercetin (393) and /3-photomethyl-quercetin (394). Excitation of the carbonyl function is followed by... 

Irvine s first publication (1899) dealt with the rotatory powers of the optically active methoxy- and ethoxy-propionic acids prepared from lactic acid. In those early days the Purdie reaction afforded so rich a field for investigation that Irvine and his collaborators continued work on various types of hydroxy bodies in addition to the sugars. There appeared papers on the isopropylidene derivatives and methyl ethers of glycerol and mannitol, and on the chemistry of benzoin and benzoin-like materials. The constitution of the glucoside salicin was studied and its pentamethyl ether was synthesized. 

Scheme 6. Synthesis of the Tolypothrix pentamethyl ether 33 according to Bruckner et al. a) 2 equiv LDA, I equiv MePh2SiCl, -78"C-rt b) 35, -78 C-rt c) Rh/C/H d) MeLi, -78X e) H.O,. PPTS ...

All OH groups of a cyclic monosaccharide are converted to ethers by treatment with base and an alkyl halide. For example, a-D-glucose reacts with silver(I) oxide (Ag20, a base) and excess CH3I to form a pentamethyl ether. 

The four ether bonds that are not part of the acetal do not react with any reagents except strong acids like HBr and HI (Section 9.14). The acetal ether, on the other hand, is hydrolyzed with aqueous acid (Section 27.7B). Aqueous hydrolysis of a single glycoside (like the pentamethyl ether of a-D-glucose) yields both anomers of the product monosaccharide. 

Purdie (Irvine-Purdie) methylation. Exhaustive methylation of a methyl glycoside by repeated treatment with methyl iodide and silver oxide, followed by hydrolysis of the pentamethyl ether with dilute acid to yield the anomeric hydroxyl group. 

In the following, selected examples for these reactions are reported. Reaction a) has been discussed in some detail already in Section IV. C examples for reaction d) are found in Section VI. A. Selective transbutylation (reaction b)) was achieved for various mono-, di- and triethers or esters of calix[4]arene, leading to tri-, di- and mono-t-butyl calix[4]arene derivatives, from which the 0-aUtyl and especially the O-acyl residues can be cleaved again if desired, or necessary. A single f-butyl group was also eliminated from the tetramethyl ether of 2b , the pentamethyl ether of and the hepta(p-bromobenzoate) of 2e °. Various other partially debutylated derivatives of 2c have been prepared analogously . ... 

Evonine has been synthesized starting with hydroxy-ester (48) by conversion into the mixed anhydride (49), followed by condensation with evoninol acetonide pentamethyl ether (50). Several simple steps then led to evonine (51) (Scheme 9). ... 

Pentamethyl ether, CjjHjjOj, crystals from petr ether, methanol or 90% alcohol, mp 144. Very so] in acetone, glacial acetic acid, bsnzene, ethyl acetate. 

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