Synthesis of novel quinoxaline-5-carboxylic acid derivatives

This paper describes the synthesis of several new 2,3-dimethoxy-6-methyl-7-nitro-quinoxaline-5-carboxylic acid derivatives ( 13a-m ) via a multistep synthetic route from 5-methyl-1H-benzo[d][1,3]oxazine-2,4-dione ( 1 ).     

Mass spectra of some derivatives of O-toluenesulphonic acid

The mass spectra of the derivatives of o-toluenesulphonic acid show a significant interaction of methyl and SO₂R groups. The change of a substituent mainly influences the decomposition mechanism of molecular ions and some fragment ions which are formed from them.¹     

The use of quinoxaline-2-carboxylic acid and its derivatives as analytical reagents

Quinoxaline-2-carboxylic acid and 3-chloro and 3-hydroxy derivatives have been studied as analytical reagents. The solubility products of the metal salts, the optimum pH range for complete precipitation and the thermal behaviours of the metal complexes have been established. Quinoxaline-2-carboxylic acid allows the gravimetric determination of Cu(II), Cd(II), Zn(II), Co(II), Ni(II) and Pd(II); with the 3-chloro and 3-hydroxy derivatives, only palladium(II) could be precipitated quantitatively.     

Mass spectra of derivatives of N-alkyl- and N-alkoxyalkylideneimine-2-carboxylic acids

The fragmentation of compounds of the RN(CH₂)_nCHCOX (n=1–5) and RNCH₂C(COX)₂ type, where X=OAlk and NH₂ and R=H, D, OAlk, and Cl, under electron impact was studied. When n=2–5, the chief fragmentation process is amine fragmentation, and the (M–COX)⁺ ion peak is the principal peak in the spectra at 30 and 12 eV. The fragmentation of three-membered heterocycles differs radically. The dominant fragmentation for 1-alkylaziridine-2-carboxylic and -2,2-dicarboxylic esters is splitting out of a radical from the ester group. This process is absent when R=H, D, C, and OAlk. Fragmentation with splitting out of the elements of alcohol for the esters and of ammonia for the amines is characteristic in the case of derivatives of 1-alkoxyaziridine-2-carboxylic and-2,2-dicarboxylic acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 624–633, May, 1977.     

Mass spectra of some neopentylphosphorus derivatives

The fragmentation patterns and major metastable ions of the mass spectra of the neopentyl-phosphorus derivatives [(CH₃)₃CCH₂]₃P, [(CH₃)₃CCH₂]₂P(O)H, [(CH₃)₃CCH₂]_nPX_3-n (n = 1 and 2; X = H, Cl, C₆H₅ and CH = CH₂), [(CH₃)₃CCH₂]₃PS, [(CH₃)₃CCH₂]_nP(S)R_3-n (n = 1 and 2; R = C₆H₅ and CH = CH₂), [(CH₃)₃ CCH₂]₂PCH₂CH₂P[CH₂C(CH₃)₃]₂, ([CH₃)₃CCH₂]₂PCH₂PCH₂-CH₂P(H)C₆H₅ and [(CH₃)₃CCH₂]₂PCH₂CH₂P(S)(CH₃)₂ are described. Fragmentation of a neopentyl group by elimination of either C₄H₈ or CH₃ is very favourable when the neopentyl group is bonded to either a tricoordinate or tetracoordinate phosphorus atom. In neopentylphosphines with two or three neopentyl groups, stepwise elimination of C₄H₈ from all of the neopentyl groups occurs very readily. The resulting [(CH₃)_nPX]^+._3-n ions are often the most intense ions in the mass spectra.     

Mass spectra of some oxadiazole derivatives

The mass spectra of some substituted oxadiazoles have been determined and analysed with the aid of high resolution mass spectrometry. Some characteristic and major differences between their spectra have been noted, and possible rationalizations have been advanced. The main fragmentation patterns of the 1,3,4-oxadiazole derivatives have been interpreted in terms of diazirine intermediates. Specific skeletal rearrangement processes have been observed in the spectra of the 1,3,4- and 1,2,4-oxadiazoles, and possible mechanisms are proposed.     

Synthesis of new 3,3-dimethoxyazetidine-2-carboxylic acid derivatives

Cyclization of γ-amino-α-bromocarboxylic esters resulted in an efficient synthesis of new 3,3-dimethoxyazetidine-2-carboxylates, that is, methyl N-t-butyl-3,3-dimethoxyazetidine-2-carboxylic ester and 3,3-dimethoxyazetidine-2-carboxylic acid, or 3-bromo-4,4-dimethoxypyrrolidin-2-ones, depending on the substituent at nitrogen. Reduction of the 3,3-dimethoxyazetidine-2-carboxylates gave the corresponding 3,3-dimethoxy-2-(hydroxymethyl)azetidines. These novel cyclic amino acid derivatives, available on multigram scale, have a suitably protected carbonyl function at the 3-position, which enables further functionalization.     

Mass spectra of some derivatives of amorphigenin

Conclusions The mass spectra of seven rotenoid compounds have been studied. The appearance of the main fragments in the mass spectra of the rotenoid is due to the cleavage of the bonds of the -pyrone ring. The molecules of the 7,8-dehydro-derivatives are more stable to electron impact.     

Mass spectra of some 4,5-dihydroimidazole derivatives

The mass spectra of a series of 4,5-dihydroimidazole derivatives were determined. Deuterium labelling and high resolution mass spectrometry were utilized in order to elucidate the mechanism of a number of fragmentations. The most significant ions arise from the following processes: (1) elimination of the C-4 substituent; (2) cleavage of the 1,2-N? C and 4,5-C? C bonds with or without hydrogen migration; (3) cleavage of the 1,5-N? C and 2,3-C? N bonds with charge retention on the N-1? C-2 moiety.

1 In this paper the standard numbering of the imidazole ring (see structures) is retained for the fragment ions.

Anomalous behaviour is shown by the t-butoxy derivative; the reasons for this behaviour are discussed.     

Mass spectra of some 1,2,4-triazole derivatives

Fragmentation of various 1,2,4-triazole derivatives occurs by two predominant pathways involving the loss of RCN originating from both C₃ and C₅ positions. The resulting diazirinium radical cation was observed to lose a nitrogen atom to give a nitrilium ion whose substitution pattern was dependent upon the original substituents in the nucleus.     

Azetidine-2-carboxylic acid derivatives

An improved method for the preparation of DL -azetidine-2-carboxylic acid is reported. The reaction of thionyl chloride with azetidine-2-carboxylic acid in methanol gave rise to 2-carbomethoxyazetidine hydrochloride, which upon treatment with triethylamine yielded 2-carbomethoxyazetidine. 2-Carbomethoxyazetidine proved to be unstable and upon standing formed azetidine-2-carboxylic acid anhydride. The nmr and ir spectra of 2-carbomethoxyazetidine are discussed in terms of its conformation. The conversion of azetidine-2-carboxylic acid to azetidine-2-carboxamide is also described.     

Syntheses and reactions of some 4,5-dihaloimidazole-2-carboxylic acid derivatives

The preparation of 5H,10H-diimidazo[1,2-a:1′,2′-d]pyrazine-5,10-dione ( 2a ) and its 2,3,7,8-tetrabromo- and 2,3,7,8-tetrachloro- analogs ( 2b and 2c , respectively) is reported. These dimers, when allowed to react with various anilines, afford imidazole-2-carboxamides ( 3a-c ).     

Mass spectra of some tropane and tropidine derivatives

Fragmentation patterns of tropane and tropidine derivatives have been shown to depend on the nature of the substituents. Unsaturation in the 6-membered ring leads to preferential fragmentation of the two carbon bridge. When the 6-membered ring is saturated and substituted with poor leaving groups (OH and CN) fragmentation of the 6-membered ring is preferred.     

Mass spectra of some dithiocarboxylic acid esters

The mass spectra of a variety of aliphatic esters of aromatic dithiocarboxylic acids are reported; their breakdown patterns are compared with those of the corresponding oxygen esters, O-alkyl thioesters and S-alkyl thioesters. Small quantities of O-alkyl thioesters present in alkyl dithioesters can be detected by the appearance of the peak [ArC?O]⁺.     

Synthesis of new acridine-9-carboxylic acid derivatives

New 1,3-dihydroxyacridine-9-carboxylic acids were obtained by Pfitzinger reaction from 2,4,6-trihydroxytoluene (methylphloroglucinol). Their bromination and azo-coupling reactions were studied. Computer simulation was used to determine potential pharmacokinetic and toxic properties of the synthesized compounds.     

Use of quinoxaline-2-carboxylic acid and its 3-chloro- and 3-hydroxy derivatives in the complexometric determination of palladium

Analytical and Bioanalytical Chemistry -