Ueber die Bromirung des Diphenylglyoxalons

Abstract

In den zwei vorhergehenden Abhandlungen 2, des gleichen Titels war gezeigt worden, dass Diphenylglyoxalon (I) in

Oxidation of uric acid. 1. Structural revision of uric acid glycols

“…The infrared spectra of 4a and 5 showed similar features; a sharp absorption band at 1804 cm'1 characteristic of the hydantoin system was also present in the spectrum of 5. The mass spectrum exhibited a fragmentation pattern similar to that of 4a; m/e 184 (M+•) -* m/e 156, and m/e Further evidence bearing on the structure 4 comes from the reaction with o-phenylenediamine or its hydrochloride which afforded the same product, 3-hydroxyquinoxaline-2-carboxyureide (6). The failure of 4a to undergo condensation into an alloxazine under acid conditions ruled out the alloxan-like structure 2a.9…”

“…Idophinite (6). This compound was prepared by the same procedure used for the preparation of glucophinite except the diol 5 was used in place of the diol 1: mp 103-105 °C; [c*]25d +78.4°( c 0.6, CHClg); NMR 0.9-1.2 (m, 10 ), 3.…”

“…The mechanism could operate with equal plausibility via an intermediate glycol 2, but this cannot as yet be assessed on the strength of the available experimental material. The mechanistic analogy for this mode of alloxan ring opening exists in the chemistry of riboflavine.9 The ureide of 3-hydroxyquinoxaline-2-carboxylic acid (6) is formed when alloxan (3) is treated with o-phenylenediamine, the latter being sufficiently basic to cleave the alloxan ring.98 If the reaction is carried out in the presence of an equivalent of mineral acid, the ring remains intact and the product is alloxazine.9b Similarly, 3 and urea failed to yield 4 in the presence of an acid.…”

Preparation of quinoxalines, dihydropyrazines, pyrazines and piperazines using tandem oxidation processes

“…10 The dihydropyrazines 3 were sometimes accompanied by N-acyl-NA-formyl-trans-1,2-diaminocyclohexane byproducts 4. There is an isolated example of the oxidative cleavage of bishemiaminals 11 and we propose a similar MnO 2 -mediated process leading to 4. 12 Having shown that it is possible to produce dihydropyrazines 3 in situ using TOP methodology, attention moved to extended one-pot procedures.…”

Tandem oxidation processes for the preparation of nitrogen-containing heteroaromatic and heterocyclic compounds

“…An isolated example of the oxidative cleavage of a bis-hemiaminal using sodium perbromate has however been reported. 15 By varying the reaction conditions and solvent (Scheme 4), we found that it was possible to minimise formation of bis-amide 7a by the addition of 2.0 M HCl in Et 2 O (1 equivalent with respect to the diamine) to the reaction mixture. Using this optimised procedure, dihydropyrazine 6a was obtained in 53% yield.…”