Substitution oxime acidity effects

Eligh yields of esters are obtained from both acid-sensitive (cyanoacetic acid) and base-sensitive carboxylic acids (3-phenyl-propionic acid and trichloroacetic acid) and, in these latter cases, use of 4-(dimethylamino)pyridinium chlorosulfite chloride is much more effective than use of thionyl chloride alone. The esterification process has been claimed to be independent of the steric environment of the carboxyl function, though this reagent may be of more limited value with heavily substituted benzoic acids. Carboxyl activation, in the presence of a primary amine, leads to the corresponding amide in excellent yield (eq 2). In both the esterification and amidation processes and the oxime dehydration reaction discussed below, recovery of DMAP is straightforward. 

Care must also be taken, when solvent extraction is used, to avoid artefacts either from impurities in the solvent themselves (Perry and Hansen, 1974) or by the extraction of some of the non-acidic and neutral components of urine into the solvents at acid pH. These latter components include urea, phenols and alcohols, particularly those derived from dietary sources. To avoid this problem prior extraction of the urine with the same solvent systems at alkaline pH before subsequent acidification and re-extraction can be effective (Mamer et al, 1971), while the first step towards exclusion of artefacts requires the use of high-purity reagents and solvents. Although seldom incorporated into the solvent extraction methods that have been described, the prior stabilization of 0X0 acids as substituted oxime derivatives is also essential to avoid artefact formation during solvent extraction, such as the oxidative decarboxylation of phenylpyruvic acid to phenylacetic acid (Thompson etal., 1975). 

The most widely used route to l-benzazepin-2-ones involves the Beckmann or Schmidt reaction of the easily accessible 1-tetralones. Many biologically active compounds described in this review have been prepared on the basis of these reactions they have been fully reviewed [2], In the Beckmann reaction of 1-tetralone oximes, polyphosphoric acid is used as a catalyst-solvent in most instances. Aryl migration generally takes precedence over alkyl migration under these reaction conditions, and various 1-tetralone oximes substituted on the aromatic and/or aliphatic rings can be converted to the appropriate 2,3,4,5-tetrahydro-l//-l-benzazepin-2-ones (51) [5, 20-23, 36, 59, 65, 80, 107-112]. Both courses of the rearrangement occur in some instances, yielding l-benzazepin-2-ones (51) and the isomeric 2-benzazepine-l-ones, probably due to electronic effects of the substituents [90, 113, 114]. 

Mechanisms have been suggested for the N-bromosuccinimide (NBS) oxidation of cyclopentanol and cyclohexanol, catalysed by iridium(III) chloride,120 of ethanolamine, diethanolamine, and triethanolamine in alkaline medium,121 and for ruthenium(III)-catalysed and uncatalysed oxidation of ethylamine and benzylamine.122 A suitable mechanism has been suggested to explain the break in the Hammett plot observed in the oxidation of substituted acetophenone oximes by NBS in acidic solution.123 Oxidation of substituted benhydrols with NBS showed a C-H/C-D primary kinetic isotope effect and a linear correlation with er+ values with p = —0.69. A cyclic transition state in the absence of mineral acid and a non-cyclic transition state in the presence of the acid are proposed.124 Sulfides are selectively oxidized to sulfoxides with NBS, catalysed by ft-cyclodextrin, in water. This reaction proceeds without over-oxidation to sulfones under mild conditions.125... 

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