2.4- Dinitrophenyl bromide

The use of 2,4-dinitn>i enyl aromatic quatemaiy salts prepared directly from the parent isoquinoline compound and 2,4-dinitrophenyl bromide or chloride enhances the electron-deficient nature of the iso-quinolinium salts, accelerates the rate of their [4 2] cycloaddition reacticms with electron-rich alkenes, and has permitted the use of isoquinolinium salts previously regarded as unmanageable. The application of these observations in the total syntheses of methylamottianamide and 14-epicoiynoline is summarized in Scheme 26. - ... 

Two experimental techniques have improved the observed participation of simple aromatic quaternary salts in [4+ + 2] cycloadditions. The addition of hydroquinone, which forms a stabilized 1 2 complex with the isoquinolinium salts, to the reaction mixture accelerates the rate of observed isoquinolinium salt [4+ + 2] cycloaddition.148b In addition, the use of 2,4-dinitrophenyl aromatic quaternary salts, prepared from the parent base and 2,4-dinitrophenyl bromide or chloride, accentuates the electron-deficient character of the quaternary salt and accelerates their participation in [4+ + 2] cycloadditions with electron-rich dienophiles.152 These observations of Falck and co-workers have proved useful for promoting the [4+ + 2] cycloaddition of isoquinolinium systems previously regarded unmanageable. The application of these observations in the total syntheses of 14-epicorynoline (16) and methyl arrnothanamide (17) have been detailed [Eq. (67)],152... 

The synthesis93 of N-(2,4-dinitrophenyl)-3-0-(tetra-0-acetyl-/ -D-glu-copyranosyl)-L-threonine methyl ester (131) involved a two-step procedure. First, formation of the intermediate, L-threonine orthoester 130 was achieved by treatment of tetra-O-acetyl-a-D-glucopyranosyl bromide (128) with the methyl ester of N-(2,4-dinitrophenyl)-L-threonine94 (129) under the conditions of the Koenigs-Knorr reaction (see next paragraph), and this was then converted into the L-threonine glycoside 131. 

Dinitrobenzenesulfenyl bromide may be similarly prepared by refluxing 2,4-dinitrophenyl benzyl sulfide with the equivalent amount of bromine in 5 parts of dry carbon tetrachloride. As it is less stable than the chloride, losing bromine if overheated, it should be concentrated on a 40° water bath under vacuum. When worked up in the same manner as the chloride, the product usually contains some is-(2,4r-dinitrophenyl) disulfide. Because the disulfide is insoluble in carbon tetrachloride, the sulfenyl bromide may be readily purified by recrystallization yield 75-80%, m.p. 102-104°. 

Aryl substituents at N2 tend to stabilize the 1-bromide center, and a range of poly-O-acetyl-a-D-glycosyl bromides with iV-benzoyl,112 N-tosyl,163-171 N-(2,4-dinitrophenyl),16S and other N-substituents168 have been prepared, all of which yield glycosides on treatment with alcohols. The N-benzoyl derivative (LXI) readily undergoes an intramolecular rearrangement112- 113 to give the oxazoline derivative hydrobromide (LXII), from which the free base (LXIII) can be prepared.113... 

Cationic surfactants with an electron rich phenyl substituent on the hydrophilic ammonium head group (phenyl, 2,4-dimethoxyphenyl, and 2,4-dimethoxybenzyl dimethylammonium bromides) were found to be more efficient catalysts than CTAB for the hydrolysis of 2,4- and 2,6-dinitrophenyl phosphates (Bunton et al., 1970). The pseudo-first order rate constants increased appreciably at low concentrations of these... 

The kinetics of the hydrolysis of A/ -(2,4-dinitrophenyl)benzhydrazonyl bromide and its derivatives have been studied over a wide range of pH. Roles for both 5n1 and 5n2 mechanisms were inferred. 

When it is desired to make 1,2-diaminobenzimidazoles, the compounds can be prepared directly from acetyl 2-aminophenylhydrazines (12) and cyanogen bromide [173, 174] with subsequent hydrolysis of the 1-amido derivative (Scheme 3.1.15). It may, however, be more convenient to Al-aminate a 2-aminobenzimidazole directly using -(2,4-dinitrophenyl)hydroxylamine or hydroxylaminc -sulfonic acid [174, 175], which gives yields in the range 40-76%. 

Peptide synthesis /-Amyl chloroformate. Bis-(2,4-dinitrophenyl)carbonate. Bis-o-phenylene pyrophosphite. i-Butyl chloroformate. sec-Butyl chloroformate. /-Butyl chloroformate. /-Butyl 2,4,5-trichlorophenyl carbonate. CopoIy(ethylene-N-hydroxymaleimide). N,N-Diethyl-I-propynylamine. Di-(p-nitrophenyl)sulfate. Ethoxyacetylene. N-Ethoxycarbonyl-2-ethoxy-l,2-dihydroquinoline. N-Ethylbenzisoxazolium fluoroborate. Ethyl chloroformate. N-Ethyl-5-phenylisoxazolium-3 -sulfonate. N-Hydroxysuccinimide trifluoroacetate. Methyl-morpholine. 4-Methylthiophenol. p-Nitrophenol. Oxalylchloride. Pentachlorophenol. Pentamethylbenzyl chloride. /-Pentyl chloroformate. Phenacyl bromide. Polyhexamethylene carbodiimide. Tetraethyl pyrophosphite. 1,2,4-Triazole. 

Alkylation (R" = alkyl or substituted alkyl) is most satisfactorily accomplished with active halogen compounds such as allyl, benzyl, and propargyl halides, but a-halo ketones, esters, and nitriles can also be used.467,474 Treating l-(l-cyclohexenyl)pyrrolidine with allyl bromide in the presence of /V-ethyl-dicyclohexylamine as base leads to introduction of two allyl groups, i.e., formation of 2,6-diallylcyclohexanone.475 Arylation can be effected by, for example, l-chloro-2,4-dinitrobenzene (R" = 2,4-dinitrophenyl).476 A-Isobutyl-fl-butylamine477 and pyrrolidine478 have been recommended as amine components for C-alkylation by simple alkyl halides such as ethyl and methyl iodides. The following two examples are illustrative ... 

Retention time 7 (free captopril (as p-bromophenaoxidized captopril (as N-(4-dimethylamino-3,5-dinitrophenyl)meileimide adduct))... 

The kinetics of 2,4-dinitrophenyl-acetate hydrolysis catalyzed by polymers containing imidazole, carboxylic acid, oxidation groups and their complexes with surfactants, such as 1-cetylpyridinium chloride and cetylundecyldimethylammonium bromide, was determined by spectrophotometry [57]. Catalytic rate constants of the second-order-rate increase with a rise in the surfactant concentration until they reach a plateau at a polymer/surfactant ratio of 1 6. Anionic surfactant does not accelerate the polymer-catalyzed hydrolysis. The catalytic mechanism of a polymer/surfactant complex enables the penetration of the substrate into a pseudophase of a soluble complex. This leads to an increase of the ester concentration in the neighbourhood of a polymer imidazole fragment and accelerates the process. Such a pseudophase promotes the protonation of imidazole rings. 

The S—aryl bond of 2,4-dinitrophenyl l-thio- -o-glucopyranoside was cleaved on treatment with benzyl bromide, the benzyl carbonium ion presumably acting as a sulphur-specific Lewis acid. ... 

Racemic (l,3/2)-l-benzyloxycarbonylamino-3-0-ethyl- and (l,2/3)-3-benzyl-oxycarbonylamino-l-O-ethyl-cyclohexanediols (prepared from 3-ethoxycyclo-hexene) have been condensed under Koenigs-Knorr conditions with 3,4,6-tri-O-acetyl-2-deoxy-2-(2,4-dinitrophenyl)amino-a-D-glucopyranosyl bromide to yield... 

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