Methyl Chloroformate attack

The addition of a-lithiomethoxyallene 144 [55] to benzaldehyde dimethylhydra-zone 145 (Eq. 13.48) leads to a mixture of pyrroline 146 and dihydroazete 147 [56]. The cydization in this case, which takes place in the same operation as the addition to the hydrazone, follows two distinct pathways, with attack of the nitrogen atom taking place at the inner, in addition to the terminal, carbon atom of the allene. A similar reaction of 144 with SAMP-hydrazone 148 (Eq. 13.49) leads to 3-pyrroline 149 in 88% yield and excellent diastereoselectivity [57]. Cleavage of the chiral auxiliary group from 149 takes place in two steps (1, methyl chloroformate 2, Raney nickel, 50 bar, 50 °C) in 74% overall yield. When the addition of 144 to 148 is conducted in diethyl ether, cydization of the adduct does not take place. Surprisingly, the hydrazones of aliphatic aldehydes react with 144 in poor yield in THF, but react quantitatively and diastereoselectively in diethyl ether to give the (uncyclized) allenyl hydrazone products. 

In such models the OH concentration field is computed using measured or estimated concentration fields of the precursor molecules and photon flux data. The resulting OH field is then tuned such that it correctly predicts the lifetime of methyl chloroform (CH3CCI3) with respect to OH radical attack. From measurements of the atmospheric turnover time of CH3CCI3 (4.8 years) [20], its lifetime with respect to loss in the stratosphere (45 years), and its lifetime with respect to loss in the oceans (85 years) the tropospheric lifetime of CH3CCI3 with respect to OH radical attack has been inferred to be 5.7 years [17,21], Methyl chloroform is the calibration molecule of choice because it has a long history of precise atmospheric measurements, it has no natural sources, its industrial production is well documented, and because the kinetics of reaction Eq. 20 are well established, feo = 1.8 x 10-12 exp(- 1500/T) cm3 molecule-1 s-1 [22]. 

METHYL CHLOROFORMATE (79-22-1) Forms explosive mixture with air (flash point 54°F/12 C). Reacts with moisture in air, forming hydrogen chloride fumes. Reacts slowly with water or steam, forming hydrochloric acid, carbon dioxide gas, and methanol. Violent reaction with alkali metals, dialkylzincs, dimethyl formamide, dimethyl sulfoxide, ethers, ethylene glycol diethyl ether, strong oxidizers. Incompatible with strong bases, alcohols. Corrodes metals in the presence of moisture. Attacks some plastics, rubber, and coatings. 

Trichloroethane 1,1,1-trichloroethane methyl chloroform 20 8 No attack little or no absorption Victrex LNP Engineering Plastics... 

Bromine in chloroform and bromine in acetic acid are the reagents used most often to brominate pyrazole. When nitric acid is used as a solvent, both bromine and chlorine transform pyrazoles into pyrazolones (Scheme 24). Thus 3-methyl-l-(2,4-dinitrophe-nyOpyrazole is brominated at the 4-position (309). The product reacts with chlorine and nitric acid to give the pyrazolone (310). The same product results from the action of bromine and nitric acid on (311). The electrophilic attack of halogen at C-4 is followed by the nucleophilic attack of water at C-5 and subsequent oxidation by nitric acid. 

Methyl- and 4-methyl-pyridinium methiodides yield cyanine-type dyes with chloroform and alcohohc potassium hydroxide, e.g. via the methylene dihydropyridine (51) with attack by dichlorocarbene at the active methylene group (cf. ref. 92a). 

The use of iodotrimethylsilane for this purpose provides an effective alternative to known methods. Thus the reaction of primary and secondary methyl ethers with iodotrimethylsilane in chloroform or acetonitrile at 25—60° for 2—64 hours affords the corresponding trimethylsilyl ethers in high yield. The alcohols may be liberated from the trimethylsilyl ethers by methanolysis. The mechanism of the ether cleavage is presumed to involve initial formation of a trimethylsilyl oxonium ion which is converted to the silyl ether by nucleophilic attack of iodide at the methyl group. tert-Butyl, trityl, and benzyl ethers of primary and secondary alcohols are rapidly converted to trimethylsilyl ethers by the action of iodotrimethylsilane, probably via heterolysis of silyl oxonium ion intermediates. The cleavage of aryl methyl ethers to aryl trimethylsilyl ethers may also be effected more slowly by reaction with iodotrimethylsilane at 25—50° in chloroform or sulfolane for 12-125 hours, with iodotrimethylsilane at 100—110° in the absence of solvent, " and with iodotrimethylsilane generated in situ from iodine and trimcthylphenylsilane at 100°. ... 

Most structural work on xylan has been done on that from esparto grass and the principal attack made by way of the methyl ether. Xylan can be methylated by heating with methyl iodide and silver oxide,92-93 but complete etherification is difficult and considerable degradation probably occurs. On the other hand, complete etherification is attained by methylation in two operations with potassium hydroxide and dimethyl sulfate to give a dimethylxylan in almost quantitative yield70 showing [< ]22d — 92° in chloroform. Methylation with potassium hydroxide appears to proceed more readily than with sodium hydroxide.70-92... 

Triazine is attacked by methyl iodide, ethyl chloroformate, and picryl chloride at N-2 (79CB1514 79CB1535 84H674). Similar treatment of 4,5,6-triphenyl-1,2,3-triazine 2-oxide gave only the 1-methyl salt no methoxy product was identified (84H674). 

Imidazoles react with chloroform at high temperature to form azines by carbene insertion and trichloromethyl radicals behave similarly, but carbenes do not always induce ring expansion. In alkaline medium, chlorodifluoromethane converts benzimidazole and its 2-methyl analogue into the 1-difluoromethyl derivatives 365. Dichlorocarbene under basic conditions N-alkylates benzimidazole, and 1-methylbenzimidazole couples under the influence of the same reagent (Scheme 69), perhaps involving initial attack of the carbene at N(3). 

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