Dimethyl carbamate, reaction

The use of NBD-Cl for the fluorescence analysis of alkylamine-generating pesticides has been investigated [173]. A two-phase reaction system is employed for the hydrolysis and labeling of N-methyl- and N,N-dimethyl-carbamate pesticides. The residue is hydrolyzed in 0.1 M sodium carbonate and the liberated amine is treated with NBD-Cl in an organic phase (IBMK, isobutyl methyl ketone) above the aqueous layer. An aliquot portion of the organic layer is used for chromatography. The reactions involved are shown in Fig. 4.65. 

This same methoxy—methyl combination reaction was used as a reference in deriving the absolute kinetic parameters of the reactions of methoxy with methyl formate [192], methyl acetate [367] and dimethyl carbamate [368] (Table 33). 

Full details are now available of Overman s procedures for [1,3] transposition of allyl alcohols using the mercuric salt-catalysed [3,3] sigmatropic rearrangement of their dimethyl carbamate derivatives (Scheme 28). The evidence suggests a cyclic intermediate (46), such that the reaction may be termed as cyclization induced . This sequence is rather limited in scope if employed as a preparative method for contra-thermodynamic isomerization of the allylic... 

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

Carbamate glycosyl donors are another useful class of compounds, which pre sent significant variability in chemical structures (Scheme 3.24). In an early example by Kunz and Zimmer, the N-allyl carbamate donors were used in a remote activation protocol to furnish pyranoside and furanoside products. In this reaction, the N-allyl carbamate donor 146 is activated with dimethyl methylthiosulfonium... 

Polymers containing pendant carbamate functional groups can be prepared by the reaction of phenyl isocyanate with poly(vinyl alcohol) in homogeneous dimethylsulfoxide solutions using a tri-ethylamine catalyst. These modified polymers are soluble in dimethyl sulfoxide, dimethylacetamide, dimethylformamide and formic acid but are insoluble in water, methanol and xylene. Above about 50% degree of substitution, the polymers are also soluble in acetic acid and butyrolactone. The modified polymers contain aromatic, C = 0, NH and CN bands in the infrared and show a diminished OH absorption. Similar results were noted in the NMR spectroscopy. These modified polymers show a lower specific and intrinsic viscosity in DMSO solutions than does the unmodified poly(vinyl alcohol) and this viscosity decreases as the degree of substitution increases. 

Under the same conditions (batch or GL-PTC) discussed for CHg-acidic compounds, primary aromatic amines also react with DMC. In this case, although the reaction yields selectively the mono-A-methylated amines with no dimethylated by-products, sizable amounts of methyl carbamates (ArNHCOgMe) are formed. ° Much better results can be gathered in the presence of zeolites, particularly alkali metal exchanged Y and X faujasites. These aluminosilicates posses pseudospheri-cal cavities (supercavities) of 11-8 A in diameter, which can be accessed through channels whose size is 7.4 kP ... 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

The nature of the aromatic substituents is apparently not critical for SSRI activity, as indicated by the structure of duloxetine (23-5), where one ring is replaced by thiophene and the other by naphthalene. The synthesis starts as above by the formation of the Mannich base (23-1) from 1-acetyl thiophene with formaldehyde and dimethyl-amine. Treatment of that intermediate with the complex from lithium aluminum hydride and the 2R,3S entantiomer of dimethylamino-l,2-diphenyl-3-methyl-butane-2-ol gives the S isomer (23-2) in high enantiomeric excess. Treatment of the aUcoxide from (23-2) and sodium hydride with 1-fluoronaphthalene leads to the displacement of halogen and thus the formation of ether (23-2). The surplus methyl group is then removed by yet another variant of the von Braun reaction that avoids the use of a base for saponifying the intermediate urethane. Thus, reaction of (23-3) with trichloroethyl formate leads to the A -demethylated chlorinated urethane (23-4). Treatment of that intermediate with zinc leads to a loss of the carbamate and the formation of the free secondary amine duloxetine (23-5) [23]. 

Daicel Chemical Industries in Japan patented a promising phosgene-free process involving the reaction of an aliphatic diamine with dimethyl carbonate (DMC) to produce carbamate esters, which are then thermally converted to the corresponding aliphatic diisocyanates [38] (Scheme 5.4). It is noteworthy that this process could be a total phosgene-free process since the reactant, DMC, can be made directly from methanol and carbon dioxide (or urea) and eliminates the use of phosgene [39]. 

The detailed mechanism of sarcosine NCA polymerisation may be radically modified by a change of solvent. For example, in dimethyl formamide this reaction is first order with respect to growing ends [see e. g. ref. (44)] instead of being second order as in nitrobenzene. The higher acidity of the former solvent reduces the basicity of the dissolved amine and, therefore, destroys its catalytic action. This effect influences also the equilibrium between the amine and the dissolved C02. In nitrobenzene, the carbamic acid produced is associated with the free amine forming the respective ammonium salt (ion-pairs), whereas in the more acidic dimethyl formamide it exists as an un-ionised acid. 

Etherification of isohexides with substituted-benzyl chloride in aqueous sodium hydroxide, or by means of sodium hydride in dimethyl sulfoxide, yields mixtures of mono- and bis-ethers, which can be conventionally separated by distillation or by column chromatography.176 The preparation of some phenyl ethers was also described, using the tosylate-phenoxide exchange reaction. Monoethers (88) synthesized in this way were transformed into carbamates (89) by reaction with sodium cyanide-trifluoroacetic acid (see Scheme 18). 

The triethylamine salt of 2,2-dimethyl-3-(3,4-methylenedioxyphenyl)-propionic acid (5.4 g amine, 11.4 g acid) was dissolved in 10 mL 11,0 and diluted with sufficient acetone to maintain a clear solution at ice-bath temperature. A solution of 6.4 g ethyl chloroformate in 40 mL acetone was added to the 0 °C solution over the course of 30 min, followed by the addition of a solution of 4.1 g sodium azide in 30 mL H20. Stirring was continued for 45 min while the reaction returned to room temperature. The aqueous phase was extracted with 100 mL toluene which was washed once with H20 and then dried with anhy drou s Mg S04. Thi s org ani c sol uti on of the azide was heated on a steam bath until nitrogen evolution had ceased, which required about 30 min. The solvent was removed under vacuum and the residue was dissolved in 30 mL benzyl alcohol. This solution was heated on the steam bath overnight. Removal of the excess benzyl alcohol under vacuum left a residue 13.5 g of l-(N-(benzyloxycarbonyl)amino)-1,1 -dimethyl-2-(3,4-methylenedioxyphenyl)ethane as an amber oil. The dimethyl group showed, in the NMR, a sharp singlet at 1.30 ppm in CDCH,. Anal. (C19H2lN04) C,H. This carbamate was reduced to the primary amine (below) or to the methylamine (see under MDMP). 

Aresta and Quaranta studied the reactivity of alkylammonium N-alkylcarbamates (RNH3)02CNHR towards a different acylating substrate, such as dimethyl carbonate (DMC) [62a, b]. Carbamate salts (RNH3)02CNHR (R = benzyl, allyl, cyclohexyl), prepared in situ from aliphatic primary amines and C02, reacted with DMC to afford N-alkyl methylcarbamates (Equation 6.6). The reaction requires mild conditions (343-363 K 0.1 MPa C02 pressure) and can be carried out in DMC used as solvent and reagent. At 363 K, carbamate esters were obtained in satisfactory yield (45-92%) with high selectivity, as side products such as ureas, N,N-dialkylcarbamate esters, and alkylated amines were formed in very small amounts. 

The synthons of oxiranes have also been used in this respect. For example, the reaction of C02 with a-bromoacylophenones in the presence of aliphatic primary amines, in methanol, afforded 3-alkyl-4-hydroxyoxazolidin-2-one derivatives under mild conditions [83a]. However, neither oc-bromoacetophenone nor a-chloroacetophenone afforded any carbamate product, and no urethanes were obtained with aromatic or aliphatic secondary amines. The proposed mechanism involved, as the first step, the formation of a 3-alkyl-2-methoxy-2-phenyloxirane intermediate, which reacted with alkylammonium carbamate to give the oxazo-lidone product (Scheme 6.16). This synthetic protocol was successfully applied to the synthesis of bis(oxazolidin-2-one) derivatives by reactions of 2-methoxy-3,3-dimethyl-2-phenyloxirane or a-bromoisobutyrophenone with C02 and aliphatic a,G)-diamines [83b],... 

Theoretical evidence for the thermal decomposition mechanism for ethyl oxam-ate, ethyl oxanilate, and ethyl A,A-dimethyl oxamate have been provided.27 Ethyl oxamate and ethyl oxanilate undergo rapid decarbonylation to give the corresponding carbamates. Ethyl A,lV-dimethyloxamate elimination reaction yields in one step, through a six-membered cyclic transition state, dimethyloxamic acid and ethylene gas. 

Upon irradiation, the pyrrolinone 35 undergoes a-cleavage to give the ethoxycyclopropyl carbamate 36 (70%).36) This reaction resembles that of 5,5-diphenyl and 5,5-dimethyl-2-cyclopentenone 37>, which yields cyclopropane derivatives under conditions normally leading to 2-cyclo-pentenone dimers. 38>. 

Photooxidation of parathion also occurred on leaf surfaces (18), together with isomerization and other reactions. Fenitro-thion (j),O-dimethyl 0-3-methyl-4-nitrophenyl phosphorothionate) and other phosphorothionate insecticides behaved similarly (19). Some pesticides do not require external reagents for photodegradation on surfaces carbamate insecticides such as carbaryl (1-naphthyl li-methylcarbamate), aminocarb (4-dimethylamino-3-methylphenyl li-methylcarbamate), and mexacarbate (4-dimethylamino-... 

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