Ethyl acetate carbamate, reactions

The deprotection of t-Boc proline ester 2a is representative of the general procedure employed, tert-Butyl carbamate (0.217 g, 1.0 mmol) and aluminium chloride (0.134 g, 1.0 mmol) doped on a neutral alumina (1.0 g) were mixed thoroughly on a vortex mixer. The reaction mixture was placed in an alumina bath inside an unmodified household microwave oven (operating at frequency 2450 MHz) and irradiated for a period of 1 min. After completion of the reaction (monitored by TLC, EtOAc-hexane, 9 1 v/v), it was neutralized with aqueous sodium bicarbonate solution and the product was extracted into ethyl acetate (2x15 mL). The ethyl acetate layer was separated, dried over magnesium sulfate, filtered, and the crude product thus obtained was purified by column chromatography to afford pure methyl ester 2b in 88% yield. 

To a 1-L, round-bottomed flask equipped with a stirring bar are added p-methoxybenzamide (10 g, 66 mmol), N-bromosuccinimide (NBS) (11.9 g, 66 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (22 mL, 150 mmol) and methanol (300 mL) (Note 1). The solution is heated at reflux for 15 min (Note 2), at which point an additional aliquot of NBS (11.9 g, 66 mmol) is added slowly. The reaction is allowed to continue for another 30 min (Note 3). Methanol is removed by rotary evaporation and the residue is dissolved in 500 mL of ethyl acetate (EtOAc). The EtOAc solution is washed with 6 N hydrochloric acid (HCI) (2 x 100 mL), 1 N sodium hydroxide (NaOH) (2 x 100 mL) and saturated sodium chloride (NaCI), and then dried over magnesium sulfate (MgS04). The solvent is removed by rotary evaporation and the product, methyl N-(p-methoxyphenyl)carbamate, is purified by flash column chromatography [50 g of silica gel, EtOAc / hexane (1 1)] to give a pale yellow solid (11.1 g, 93%), which is further purified by recrystallization from 500 mL of hexane (Note 4). Another... 

The crude product obtained was purified by column chromatography over silica gel with 1 1 ethyl acetate-hexane as the eluant to secure the final compound (229) in 55% yield. Careful isolahon and characterization showed that one of the major by-products of this reaction to be the bisurea derivative (259) in yields of up to 20%. We explored phe-nylchloroformate as a substitute to triphosgene in the preparation of unsymmetrical urea derivatives. Phenylchloroformate (260) in the presence of an appropriate base on reaction with an amine (241) gave the corresponding carbamate, which on further reaction with A-methyl hydroxylamine gave a urea derivative (229). However, the formation of bisurea... 

Enzymatic reaction can be used for the analysis of not only organic phosphorous chemical agents, but also organic phosphorous pesticides and carbamates, as these compounds also inhibit cholinesterase, and can occur together with CWA in field conditions. Therefore, methods have been developed for differentiating cholinesteraseblocking pesticides and organic phosphorous CWA. Ten insecticides and soman and VX were separated on a plate with silica gel. A mixture of dichloroethane and ethyl acetate (9 1) was used as the mobile phase. Analyzed chemicals were identified with selective reactions. Total time of the analysis did not exceed 30 min. 

A mixture of aldehyde (1 6 mmol), beta-naphthol/phenol (2 1 mmol) and amide/carbamate/ urea (3 1.1 mmol) and ethylammonium nitrate (EAN 0.8 mmol) was stirred at room temperature for 1 h (the completion of reaction was monitored by TLC). On completion of reaction, the reaction mixture was extracted thrice with 10 mL ethyl acetate. The extract was dried over anhydrous sodium sulfate, evaporated under vacuum to obtain the crude product which was then purified by chromatographic column on silica gel (hexane/ethyl acetate, 70 30) to yield pure 1-amido- and 1-carbamato-alkyl naphthol/phenol 4. The recovered EAN was subjected to high vaccum at 80 °C to remove the water and then reused. All the isolated reaction products were characterized and confirmed by NMR. 

Acylation. Reaction conditions employed to acylate an aminophenol (using acetic anhydride in alkaU or pyridine, acetyl chloride and pyridine in toluene, or ketene in ethanol) usually lead to involvement of the amino function. If an excess of reagent is used, however, especially with 2-aminophenol, 0,A/-diacylated products are formed. Aminophenol carboxylates (0-acylated aminophenols) normally are prepared by the reduction of the corresponding nitrophenyl carboxylates, which is of particular importance with the 4-aminophenol derivatives. A migration of the acyl group from the O to the N position is known to occur for some 2- and 4-aminophenol acylated products. Whereas ethyl 4-aminophenyl carbonate is relatively stable in dilute acid, the 2-derivative has been shown to rearrange slowly to give ethyl 2-hydroxyphenyl carbamate [35580-89-3] (26). 

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. 

Aluminum porphyrins with alkoxide, carboxylate, or enolate can also activate CO2, some catalytically. For example, Al(TPP)OMe (prepared from Al(TPP)Et with methanol) can bring about the catalytic formation of cyclic carbonate or polycarbonate from CO2 and epoxide [Eq. (6)], ° - and Al(TPP)OAc catalyzes the formation of carbamic esters from CO2, dialkylamines, and epoxide. Neither of the reactions requires activation by visible light, in contrast to the reactions involving the alkylaluminum precursors. Another key difference is that the ethyl group in Al(TPP)Et remains in the propionate product after CO2 insertion, whereas the methoxide or acetate precursors in the other reactions do not, indicating that quite different mechanisms are possibly operating in these processes. Most of this chemistry has been followed via spectroscopic (IR and H NMR) observation of the aluminum porphyrin species, and by organic product analysis, and relatively little is known about the details of the CO2 activation steps. 

Intermolecular addition and addition-cyclization reactions of aminium cation radicals with electron-rich alkenes such as ethyl vinyl ether (EVE) allow an entry into products containing the N—C—C—O moiety of 13-amino ethers 70 or the equivalent of /3-amino aldehydes 71. The mild conditions under which aminium cation radicals are generated from PTOC carbamates makes the reactions described in Scheme 22 possible. In the absence of hydrogen atom donors, the /3-amino ethoxy(2-pyridylthio) acetal 71 was the major product. The mixed acetal can easily be converted... 

The cyclohexene 121, which was readily accessible from the Diels-Alder reaction of methyl hexa-3,5-dienoate and 3,4-methylenedioxy-(3-nitrostyrene (108), served as the starting point for another formal total synthesis of ( )-lycorine (1) (Scheme 11) (113). In the event dissolving metal reduction of 121 with zinc followed by reduction of the intermediate cyclic hydroxamic acid with lithium diethoxyaluminum hydride provided the secondary amine 122. Transformation of 122 to the tetracyclic lactam 123 was achieved by sequential treatment with ethyl chloroformate and Bischler-Napieralski cyclization of the resulting carbamate with phosphorus oxychloride. Since attempts to effect cleanly the direct allylic oxidation of 123 to provide an intermediate suitable for subsequent elaboration to ( )-lycorine (1) were unsuccessful, a stepwise protocol was devised. Namely, addition of phenylselenyl bromide to 123 in acetic acid followed by hydrolysis of the intermediate acetates gave a mixture of two hydroxy se-lenides. Oxidative elimination of phenylselenous acid from the minor product afforded the allylic alcohol 124, whereas the major hydroxy selenide was resistant to oxidation and elimination. When 124 was treated with a small amount of acetic anhydride and sulfuric acid in acetic acid, the main product was the rearranged acetate 67, which had been previously converted to ( )-lycorine (108). 

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