Arylcarbamates

In acid solution 1-acyl-1//-azepines and alkyl l//-azepine-l-carboxylates undergo rapid aromatization to A-arylcarbamates,115,139,142 whereas 1/Z-azepine-l-carbonitrile suffers quantitative rearrangement and hydrolysis to phenylurea.163 Rearrangement of ethyl l//-azepine-l-carboxylate to ethyl A-phenylcarbamate is also rapid (5 min) and quantitative with boron trifluoride-diethyl ether complex in benzene.245... 

Polymer Matrix Effects. In order to approximate the environment experienced by the arylcarbamate moieties in coatings based on aromatic diisocyanates, we chose to study the photochemistry of alkyl N-arylcarbamates in polymethacrylate (PMMA) and polypropyl-methacrylate (PPMA) films. First, however, 2a and 3a were irradiated in ethyl propionate (a model solvent for PMMA and PPMA) to determine the effect of the solvent polarity (dielectric) on the photolysis of the carbamates. Upon excitation at 280 nm, where the solvent absorbance was negligible, is 0.006 for 2a and 0j) is 0.005 for 3a. These values are significantly smaller... 

Molecular Orbital Description of Arylaminyl Radicals. Aryl-aminyl radicals, as previously discussed, are intermediates in both the photolysis of alkyl N-arylcarbamates (7, 8) and the photolysis of arylamines (18). A simplified mechanism for photolysis of arylamines and alkyl N-arylcarbamates is illustrated in Scheme IV for the general case. An indication of the reactivity of the... 

The reaction of ethyl A-arylcarbamates 3 with l-bromo-3,3-dimethyl-2-buta-none or l-bromo-3-ethyl-3-methyl-2-pentanone 4 in the presence of lithium bis(trimethylsilyl)amide (LiHMDS) results in the one-step synthesis of 3-aryl-5-ferf-butyl-2(3/T)-oxazolones 7 in fair to good yields (Fig. 5.2 Table 5.1, Fig. 5.3). This method is efficient for the preparation of bulky 5-substimted-2(37f)-oxazo-lones. 

Treatment of l,3-dihalo-2-propyl and 2,3-dichloropropyl A7-arylcarbamates 11 and 14 with ammonium fluoride results in the regioselective transformation to the 2(3f/)-oxazolones 12 and 15 or to the exocyclic methylene derivatives 13 and 16 depending on the temperature (Fig. 5.5). ... 

TABLE 5.1. SYNTHESIS OF 3-ARYL-5-tert-BUTYL-2(3H)-OXAZOLONES FROM ETHYL A-ARYLCARBAMATES AND a-BROMO KETONES"... 

B, Preparation of S olid Derivatives, such as a)Esters of benzoic acid and nitrobenzoic acids (p331) b)Alkyl N-Arylcarbamates (Phenyl- and a-Naph-thy lure thanes) (p331) and e)Bis (triphenylmethyl) Esters (p332)... 

An alternative method for cleaving carbamates is exhaustive reduction with LiAlFLt to yield methylamines (Entry 3, Table 3.22). Entry 9 in Table 3.22 is an example of the nucleophilic cleavage of a carbamate with sodium methoxide. The mild reaction conditions required in the case are attributable to the structure of the amine (a vinylogous amide) these conditions are unlikely to lead to the cleavage of simple A-alkyl- or A, A-dialkylcarbamates, although A-arylcarbamates are also susceptible to nucleophilic cleavage (Entry 6, Table 3.26). 

The kinetics of reaction of O-(A-ary I carbamoyl) be n zop h cn o n c oximes in NaOMe-MeOH to give benzophenone oxime sodium salt and the corresponding methyl N-arylcarbamates have been studied.6 The Hamnett constants pobs = 0.68 and pkl = —1.32 have been estimated for the E cBR process for which 2 governs conversion of the intermediate ArNrC02N=CPh2 to ArN=C=0 and Ph2C=NO. ... 

In contrast to aliphatic amines, aromatic amines hardly react with C02 [21a] because of their poorer basicity. However, in the presence of suitable auxiliary bases (B) (such as amidines or penta-alkylguanidine superbases), carbamate salts (BH)02CNRAr (R = H, alkyl) can be generated in solution, as supported by spectroscopic and reactivity data [29]. It has been shown that even tributylamine may be effective if a suitable alkali metal salt is also present in solution in the latter case, the N-arylcarbamate has been isolated as an alkali salt (Equation 6.3)... 

Pussemier, L., R. DeBorger, P. Cloos, and R. VanBladel. 1989. Relation between the molecular structure and the adsorption of arylcarbamate, phenylurea and anilide pesticides in soil and model organic adsorbents. Chemosphere 18(9/10) 1871-1882. 

HPLC was used to evaluate the enantiomeric resolution of dihydrope-pidine enantiomers (including nimodipine), using phenylcarbamates of polysaccharides as a chiral stationary phase [35]. A column (25 cm x 4.6 mm) packed with the arylcarbamate derivatives of amylase, cellulose, and xylem was used. Detection was effected using polarimetry at 435 nm. Using xylem bis-(3,5-dichlorophenylcarbamate) and a mobile phase (flow rate of 0.5 mL/min) of 0.1%, diethylamine in hexane-propan-2-ol (17 3) yielded separation of nimodipine. 

The carbamate esters fall into two general classes according to their chemical structure and biological activity. The 7V-methylcarbamates are insecticides while the iV-arylcarbamates are mainly herbicides. Since this classification is not entirely rigorous and they are structurally related, both classes are here considered together. 

In a similar manner, y-chloropropyl arylcarbamates formed from aromatic amines and y-chloropropyi chioroformate are converted to y-atylamino-propanols. ... 

Dimethylpropananilide and A-arylcarbamate 14 undergo or/Ao-lithiation with a solution of butyllithium or ierf-butyllithium in tetrahydrofuran. When the resulting dianion is quenched with a nitrile, cyclization of the primary products occurs spontaneously in the reaction medium to give the corresponding quinazoline derivatives 15a and... 

Pussemier, L., De Borger, R., Cloos, P. and Van Bladel, R. (1989). Relation Between the Molecular Structure and the Adsorption of Arylcarbamate, Phenylurea and Anilide Pesticides in Soil and Model Organic Adsorbents. Chemosphere, 18,1871-1882. 

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