Oxygen dimethyl sulfate

Carbon is alkylated ia the form of enolates or as carbanions. The enolates are ambident ia activity and can react at an oxygen or a carbon. For example, refluxing equimolar amounts of dimethyl sulfate and ethyl acetoacetate with potassium carbonate gives a 36% yield of the 0-methylation product, ie, ethyl 3-methoxy-2-butenoate, and 30% of the C-methylation product, ie, ethyl 2-methyl-3-oxobutanoate (26). Generally, only one alkyl group of the sulfate reacts with beta-diketones, beta-ketoesters, or malonates (27). Factors affecting the 0 C alkylation ratio have been extensively studied (28). Reaction ia the presence of soHd Al O results mosdy ia C-alkylation of ethyl acetoacetate (29). 

The hydroxythiophenes which exist predominantly as the thiolen-2-ones also show reactions characteristic of the enol form. They can be methylated at the oxygen with dimethyl sulfate of diazomethane and they can also be acylated. - - They also react as thio-lene-2-ones showing a reactive methylene group which can be condensed with benzaldehyde. The danger of using chemical reactivity data for drawing conclusion as to the physical state of these tautomerizable systems has been pointed out. ... 

Then, contrary to our previous hypothesis, the reaction proceeds via a Bai2 displacement of aniline on DMC. The product, mono-A -methyl aniline (PhNHMe), plausibly adsorbs into the zeohte in a different way with respect to anihne, because different H-bonds (N H — O-zeolite) take place with the solid. As recently reported by Su et al., A-methyl amines also may interact with NaY by H-bonding between the protons of the methyl group and the oxygen atoms of the zeolite this probably forces the molecule a bit far from the catalytic surface in a fashion less apt to meet DMC and react with it. This behavior can account for the mono-A-methyl selectivity observed, which is specific to the use of DMC in the presence of alkali metal exchanged faujasites in fact, the bis-A-methylation of primary aromatic amines occurs easily with conventional methylating agents (i.e., dimethyl sulfate). ... 

The 5-methyl derivative 43 was obtained from pyrido[l,2-h]cinnolin-6-ium hydroxide inner salt 17 (R = H) with dimethyl sulfate (74JHC125). Protonation of 17 (R = H) occurred on the 5-nitrogen and not the oxygen, but its 1,2,3,4,7,8,9-octahydro derivative 45 was protonated on the oxygen to produce the 11-hydroxy salt. 

The 1,3,4-thiazaphospholes are colorless, yellow, or red crystalline solids <85AG125> the 2-phenyl derivative is a pale yellow liquid. They are not oxidized by atmospheric oxygen or sulfur <86PS(28)7i>. Dimethyl sulfate or trimethyloxonium tetrafluoroborate methylates the nitrogen atom <85AG125,... 

Methylation of carbazole phenolic oxygen has been achieved using dimethyl sulfate without reaction at nitrogen. Demethylation of carbazole methyl ethers has been achieved with hydrobromic acid-acetic acid, boron trichloride,and pyridine hydrochloride. Selective demethylation of methoxyl ortho to an aldehydo function has been achieved using boron trifluoride. ° ° Partial demethylation of 1-methoxy-3-formylcarbazole occurred during Wolff-Kischner reduction." ... 

Di-te/Y-butyl-4//-thiopyran (363) as well as its 4-methyl derivative 243 were readily aromatized to thiopyrylium salts 403 using trityl tetra-fluoroborate.286 2,4,6-Triphenyl-4//-thiopyran (45) (R = Ph) was analogously converted to salts 404 by the action of methyl iodide, dimethyl sulfate, triethyloxonium tetrafluoroborate,39 perchloric acid,362 or oxygen in acetic acid.363... 

Fused oxygen and nitrogen-containing rings may also be prepared in reactions with thioureas thus, dihydrobenzoxazine products are obtained on treatment of salicyloyl chloride with thioureas371 or on fusion of salicylate esters with thiopseudoureas.320 When the thio-pseudoureas are treated with o-aminophenol, the products are benzoxa-zoles.320 A naphthyl analog of a benzoxazole is produced on treatment of l-(2-hydroxy-l-naphthyl)-2-thiourea with dimethyl sulfate.372... 

The location of the metal cation (or cations) in alcoholates has been investigated by the method of substitutive methylation for the sodium derivatives of methyl a-D-glucopyranoside, amylose, and cellulose. The method assumes that methylation by either dimethyl sulfate or methyl iodide occurs only at an anionic oxygen atom. Lenziu methylated the mono-sodium alcoholates (prepared in boiling, butanolic sodium hydroxide by the... 

Dimethyl carbonate is an interesting material which can be used instead of toxic dimethyl sulfate as a multipurpose alkylating reagent.438-578 Its synthesis can be performed in one step from cheap methanol, CO and oxygen materials in the presence of copper salts (e.g. copper(ll) methoxychloride or CuCl/py) at ca. 100 °C and 15-70 atm (equation 290).578,62S This reaction is thought to proceed in two steps 578 (a) formation of copper(II) methoxychloride from the reaction of copper(I) chloride, 02 and methanol (equation 291) and (b) reduction of copper(II) methoxychloride with CO to form dimethyl carbonate and regenerate copper(I) chloride (equation 292).626... 

Non-deprotonated amides are weak nucleophiles and are only alkylated by trialkyl -oxonium salts or dimethyl sulfate at oxygen or by some carbocations at nitrogen [16, 83]. Alkylation with primary or secondary alkyl halides under basic reaction conditions is usually rather difficult, because of the low nucleophilicity and high basicity of deprotonated amides. Non-cyclic amides are extremely difficult to N-alkylate, and few examples of such reactions (mainly methylations, benzylations, or allyla-tions) have been reported (Scheme 6.21). 4-Halobutyramides, on the other hand, can often be cyclized to pyrrolidinones in high yield by treatment with bases (see Scheme 1.8) [84—86]. 

Figure 3-40. The three different kinds of oxygen-sulfur-oxygen bond angles in the dimethyl sulfate molecule as determined by electron diffraction [96],...

Even poor nucleophiles such as the amides 46 can react with azines in the presence of alkynes as activating agents [59, 60]. Various nucleophiles (including alkoxides, thiols, amines and nitrogen heterocycles) were recently employed in a related process with Ai-oxide azaindoles (Reissert-Henze reaction. Scheme 10). In the process, the oxygen is alkylated with dimethyl sulfate and, after the nucleophilic attack, methanol is released to aromatize the initial adduct [61,62]. Following similar mechanistic trends, V-heteroatom-activated azines afford the corresponding substituted adducts. Likewise, W-tosylated isoquinoline [63, 64] and W-fluoropyridinium salts [65] are also reactive substrates in Reissert-Henze type processes. 

Sulfur-Oxygen Compounds (Thiosulfonates, Bunte Salts, Dimethyl Sulfate)... 

In alkaline solutions, xanthine alkylates on nitrogen in the order N-3, N-7, N-1, i.e. in decreasing order of acidity, and substitution is easier when the first position has been alkylated so to this extent dialkyl derivatives tend to be most easily produced. Thus 3,7-dimethylxanthine (theobromine) is produced by methylation of xanthine or 3-methylxanthine with methyl iodide and barium carbonate (33JCS662) or dimethyl sulfate in potassium hydroxide at 60 °C (50CB201). However when the oxygen functions are blocked by trimethylsilylation, alkylation occurs at N-7 (64CB934). 

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