Ether formation diazomethane

Different competitive processes are dependent on the diazo compound, on the unsaturated system, and on the solvent. With 1,1,1-trifluorobutan-2-one and diazomethane, the corresponding oxirane is formed almost exclusively. While methyl trifluoropyruvatc reacts with diazomethane to provide a mixture of the oxiranes, reaction of the pyruvate with ethyl diazoacetate provides a stable [3-1-2] cycloadduct.Chiral fluoroalkyl-substituted /i-oxo sulfoxide (e.g., 1) readily react with diazomethane to provide the corresponding chiral epoxides. Use of methanol as solvent favors oxirane formation over the competitive enol ether formation. 

Ether formation by replacement of nitrogen by oxygen alkylation by diazomethane... 

There are very few exceptions. The most important are the methylation of alcoholic and carboxylic OH groups with diazomethane. This reaction is used for cases where high yields and mild conditions are required, e. g., for expensive hydroxy compounds like certain natural products. The methyl ester formation as well as the methylation of phenols does not need an acid catalyst as these substrates catalyze themselves the dediazoniation. For ether formation an acid catalyst, e. g., HBF4, is added (except from phenols). Typical is the methylation of 3)ff-hydroxycholestane, which proceeds in dichloromethane in 95 0 yield, as shown in the Organic Syntheses method of Neeman and Johnson (1973). Analogously, ethers can be transferred in dialkylmethyloxonium salts, as described in another Organic Syntheses procedure (Helmkamp and Pettitt, 1973) for the formation of a trimethyloxonium salt obtained... 

As mentioned in Section 8.1, carbenes easily undergo insertion into O-H bonds. At an early date, Kerr et al. (1967) found that in the photolysis of diazomethane- er butanol mixtures insertion is eleven times faster at O - H than at C - H bonds. The relative rates of ether formation for methanol, ethanol, 2-propanol, and tert-butanol are 2.01 1.95 1.37 1.00. Before that investigation, Kirmse (1963) postulated that diphenylcarbene is protonated to form the diphenylmethyl carbocation, which, as a strong electrophile, adds to the alcoholate anion (or to the alcohol followed by deprotonation) forming the ether (8-26 a). Bethell et al. (1969, 1971), however, favored an electrophilic attack of diphenylcarbene at the O-atom, i. e., an ylide intermediate on the basis of isotope effects (8-26 b). Finally, a concerted process via the transition state 8.39 may be feasible (8-26 c). 

Diazomethane is not ideal for esterification of phenolic acids because the phenolic hydroxyl groups are also methylated, albeit at a slower rate, which may lead to mixtures of partially methylated products. However, esterification can usually be achieved without O-methyl ether formation by cooling the reaction mixture to below 0°C [54,55]. 

Attempts were made to overcome the problems of partial ether formation with hydroxy and phenolic acids by the use of the trimethylsilyl ether methyl ester derivatives. Dalgliesh et al. (1966) esterified the carboxylic acid groups in organic acids using diazomethane and a short reaction time (<1 min) with immediate evaporation of the reagent and solvent, followed by... 

Identification of the product(s) resulting from the reaction of heterocyclic compounds with diazomethane has been used in attempts to elucidate their tautomeric composition (for summaries, see references 7 and 41). This work was based on the assumption that if a compound which is capable of existing in both an —NH and an —OH form produced only the =NMe derivative when it w as treated with diazomethane, it existed entirely in the =NH form. On the other hand, formation of the —OMe derivative was interpreted to mean that a finite amount of the compound existed in the —OH form. In some cases the tautomer present in the solid state w as concluded to be different from that present in solution for example, 41 42 gave a higher proportion of the 3,4-dimethoxy derivative when ethereal diaz-... 

While Kakisawa et al. (87TL3981) reported formation of Wmethylpyrazole 1, Yamaguchi et al. obtained the NH derivative 2 by reaction of caryoynencins with diazomethane in ethyl acetate at 0°C (94BSJ1717 95JMC5015). The 1,3-dipolar addition was quite sensitive to the solvent employed, and a very low yield of pyrazole derivative 2 was obtained in ether or methanol (Scheme 5). 

If the carbonyl grou]) in the 3-position of N-methylisatin or tlii-ana])hthencquinone is blocked by formation of an oxime (cf. 112), A -methylation of the oxime group occurs instead of ring expansion on reaction with diazomethane. In methanol, thianaphthenequinone oxime iV-mcthyl ether (113) then undergoes ring opening catalyzed by diazoniethane (113 114). 

Another procedure consists of bubbling of sulfur dioxide through a chilled solution of diazomethane in ether . Evaporation of the solvent leaves the crude thiirane dioxide, which can be further purified by either distillation under reduced pressure or recrystallization. The formation of the thiirane dioxides is usually accompanied by formation of the corresponding olefins, along with small amount of ketazines. 

The application of phase-transfer catalysis to the Williamson synthesis of ethers has been exploited widely and is far superior to any classical method for the synthesis of aliphatic ethers. Probably the first example of the use of a quaternary ammonium salt to promote a nucleophilic substitution reaction is the formation of a benzyl ether using a stoichiometric amount of tetraethylammonium hydroxide [1]. Starks mentions the potential value of the quaternary ammonium catalyst for Williamson synthesis of ethers [2] and its versatility in the synthesis of methyl ethers and other alkyl ethers was soon established [3-5]. The procedure has considerable advantages over the classical Williamson synthesis both in reaction time and yields and is certainly more convenient than the use of diazomethane for the preparation of methyl ethers. Under liquidrliquid two-phase conditions, tertiary and secondary alcohols react less readily than do primary alcohols, and secondary alkyl halides tend to be ineffective. However, reactions which one might expect to be sterically inhibited are successful under phase-transfer catalytic conditions [e.g. 6]. Microwave irradiation and solidrliquid phase-transfer catalytic conditions reduce reaction times considerably [7]. 

Reaction of diaryl ditellurides with diazomethane-formation of diaryl telluroketals (typical procedure). Di-p-methoxyphenyl ditelluride (2.34 g, 5 mmol) in ether (30 mL) is treated dropwise, at 0°C and while stirring, with an ethereal solution of diazomethane until disappearance of the red colour of the ditelluride. Evolution of N2 ensues. The product is obtained by evaporation of the solvent. RecrystaUization from hexane or EtOH gives colourless crystals (2.41 g (100%) m.p. 98-99°C). 

Attempts to generate thiocamphor (5)-methylide (44) by the addition of diazomethane to thiocamphor and subsequent N2-elimination from the [3-1-21-cycloadduct 43 led to enethiol ether 45 via a 1,4-H shift (Scheme 5.17). The formation of an unstable intermediate 43 was proposed on the basis of the proton nuclear magnetic resonance ( H NMR) spectrum of the crude mixture. The postulated intermediate 44 could not be intercepted by dipolarophiles or methanol, and did not undergo electrocyclization to give the corresponding thirrane (41). 

C. Diazomethane. Sodium cyclohexoxide method (Note 10). A solution of sodium cyclohexoxide is prepared from 4 g. of sodium and 100 ml. of cyclohexanol (Note 11) in a 2-1. flask the cyclohexanol is heated to boiling under reflux to speed up the formation of the alkoxide. As soon as the sodium has disappeared, heating is discontinued and the condenser is removed. When solid begins to separate from the solution, the mixture is stirred with a stout rod to prevent the formation of a hard cake. The flask is surrounded by an ice bath, and, when the temperature of the mixture has dropped to 10°, 300 ml. of dry ether and a solution of 49 g. (0.33 mole) of N-nitroso-j8-methylaminoiso-butyl methyl ketone dissolved in 600 ml. of dry ether are added. The flask is connected to a 25-cm. fractionating column and an efficient water-cooled condenser (Note 12). The delivery end of the condenser should be connected to an adapter which dips below the surface of 50 ml. of ether contained in a 1-1. Erlenmeyer... 

The cyclohexanol may be replaced by benzyl alcohol. Benzyl alcohol is reported to give a slightly increased rate of formation of diazomethane and a slightly more concentrated ethereal solution however, the over-all yield is somewhat lower. If only a small amount of diazomethane is wanted, concentrated aqueous sodium hydroxide may replace the solution of the alkoxide of cyclohexanol. The yield under these conditions is 40-50%. 

Unusual bridging (//-cyclopropyIidene)diiron complexes having a tetrahedral carbene carbon have been studied as model intermediates in carbon-carbon bond formation in the Fischer-Tropsch synthesis248. The cyclopropylidene complexes cis- and trans-[Cp(Co)Fe]2(/(-Co)(//-C,H4) were readily prepared by cyclopropanation in ether, of the corresponding cis- and mww-vinylidene complexes [CpCoFe](//-CO)(//-CH2) with diazomethane in the presence of CuCl (equation 181). Both isomers are air stable in the solid state. Solutions of the complexes are air stable for several hours, provided they are kept in the dark. The pure //-cyclopropylidene isomers slowly interconvert in solution, like their parent /z-vinylidene and other alkylidene complexes. The final equilibrium ratio cis .trans = 4.8 1 is reached after two weeks. 

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