Selective O-methylation

Electrophilic substitution at the arylamine 709 using the complex salt 602, provided the iron complex 725 quantitatively. Sequential, highly chemoselective oxidation of the iron complex 725 with two, differently activated, manganese dioxide reagents provided the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727) via the non-cyclized quinone imine 726. Demetalation of the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727), followed by selective O-methylation, provided hyellazole (245) (599,600) (Scheme 5.70). 

Noleto, G.R., C.A. Tischer, P.A.J. Gorin, M. Iacomini, and M.B.M. Oliveira. 2003. Complexes of sodium vanadatc(V) with methyl a-D-mannopyranoside, methy a- and P-D-galactopyranoside, and selected O-methylated derivatives A 51V and 13C NMR study. Carbohydrate Research 338 1745-1750. 

Cs-X has also been used to promote the selective O-methylation of phenol with dimethyl carbonate. 2 N-Monomethylaniline was obtained in 93% yield by reacting aniline with dimethyl carbonate over a K-Y catalyst at 180°C (Eqn. 22.46). 3 The reaction of alcohols with chloromethyl ether over Na-Y gave the resulting methoxymethyl ethers in 70%-90% yields (Eqn. 22.47). 4... 

CATALYSIS BY RARE EARTH PHOSPHATE II SELECTIVE O-METHYLATION OF PHENOLS BY METHANOL IN VAPOR PHASE... 

A -Benzyltetrahydroisoquinolines.—A new alkaloid is corgoine (230) found in Corydalis gortschakovii (Fumariaceae). Selective O-methylation with diazomethane produced the known alkaloid sendaverine (231). ... 

A fundamental study of sohd-state NMR of selectively O-methylated celluloses obtained from de novo-synthesis ° ° has been published, which establishes the basis for rapid analysis of methyl patterns in methyl eelluloses. ... 

A further point of interest concerns the reaction of the iminium salts 118 and 120 with borohydride (65). The reduction of 118 or 120 with sodium borohydride gave an identical product mixture in which the major components were 6-0-methylmesembranol (121) and 6 -0-methyl-7a-epimesem-branol (122) in 78% and 16% yields, respectively (see Scheme 32). Two minor components representing less than 6% of the total products were identified as mesembrane and its C-7a epimer 123. While the structures of the compounds with a trans ring fusion rested on spectral evidence, the identity of 6-0-methylmesembranol was established by its synthesis from mesembranol by selective O-methylation of the sodium salt with methyl-p-toluenesulfonate, while that of c -mesembrane was identified by comparison with an authentic sample. 

Van Dyk MS, Steynberg JP, Steynberg PJ, Ferreira D. Selective O-methylation of polyhydroxyflavan-3-ols via benzylcarbonates. Tetrahedron Lett 1990 31 2643-2646. 

MeSSiMe3 or PhSSiMe3, Znl2, Bu4N I. In this case the 6-O-methyl ether was cleaved selectively from permethylated glucose. 

Second generation COMT inhibitors were developed by three laboratories in the late 1980s. Apart from CGP 28014, nitrocatechol is the key structure of the majority of these molecules (Fig. 3). The current COMT inhibitors can be classified as follows (i) mainly peripherally acting nitrocatechol-type compounds (entacapone, nitecapone, BIA 3-202), (ii) broad-spectrum nitrocatechols having activity both in peripheral tissues and the brain (tolcapone, Ro 41-0960, dinitrocatechol, vinylphenylk-etone), and (iii) atypical compounds, pyridine derivatives (CGP 28014,3-hydroxy-4-pyridone and its derivatives), some of which are not COMT inhibitors in vitro but inhibit catechol O-methylation by some other mechanism. The common features of the most new compounds are excellent potency, low toxicity and activity through oral administration. Their biochemical properties have been fairly well characterized. Most of these compounds have an excellent selectivity in that they do not affect any other enzymes studied [2,3]. 

Mannisto PT, Kaakkola S (1999) Catechol-O-methyl-transferase (COMT). Biochemistry, molecular biology, pharmacology, and clinical efficacy of the new selective COMT inhibitors. Pharmacol Rev 51 593-628... 

The catalytic activity of Mg/Al/O sample in m-cresol gas-phase methylation is summarized in Figure 1, where the conversion of m-cresol, and the selectivity to the products are reported as a function of the reaction temperature. Products were 3-methylanisole (3-MA, the product of O-methylation), 2,3-dimethylphenol and 2,5-dimethylphenol (2,3-DMP and 2,5-DMP, the products of ortho-C-methylation), 3,4-dimethylphenol (3,4-DMP, the product of para-C-methylation), and poly-C-methylated compounds. Other by-products which formed in minor amounts were dimethylanisoles, toluene, benzene and anisole (not reported in the Figure). 

The effect of temperature on the catalytic performance of Mg/Fe/O is reported in Figure 3. The behavior was quite different from that of the Mg/Al/O catalyst. The conversion of m-cresol with Mg/Fe/O was always lower than that with Mg/Al/O. The selectivity to 3-MA was almost negligible in the whole range of temperature. The selectivity to polyalkylates and to 3,4-DMP was also much lower than that observed with Mg/Al/O. Therefore, the catalyst was very selective to the products of ortho-C-methylation, 2,3-DMP and in particular 2,5-DMP. This behavior has to be attributed to specific surface features of Mg/Fe/O catalyst, that favor the ortho-C-methylation with respect to O-methylation. A different behavior of Mg/Al/O and Mg/Fe/O catalysts, having Mg/Me atomic ratio equal to 4, has also been recently reported by other authors for the reaction of phenol and o-cresol methylation [5], The effect was attributed to the different basic strength of catalysts. This explanation does not hold in our case, since a similar distribution of basic strength was obtained for Mg/Al/O and Mg/Fe/O catalysts [4],... 

The figure below illustrates proposed sites of action of drugs. Tor each drug listedt select the site of action that the drug is most likely to inhibit (a, a receptor iT J3 receptor COMTt cat e cho l-O-methyl transferase MAOt monoamine oxidase NET norepinephrine NMNt normetanephrine). 

Ethoxycarbonyl chloride is, by virtue of resonance involving the ester function, less reactive than acetyl chloride, and the reagent has found application for selective O-acylation in the steroid field.34 With this reagent, methyl 4,6-O-benzylidene-a-D-glucopyranoside yielded35 2- and 3-esters in the ratio 24 1, and the related benzyl-thiocarbonyl chloride gave the 2-ester in 58% yield.36... 

CHEC-II(1996) <1996CHEC-II(8)345> covered a range of reactions of substituents, including hydrolyses of esters to carboxylic acids and geminal dihalides to aldehydes, reduction of aldehydes and halogens directly attached to the ring, O-methylation with diazomethane, and reduction of nitroso compounds. A selection of reactions which have... 

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