Special Groups of Heterocyclic Compounds

Snedden, in Advances in Mass Spectrometry (R. M. Elliot, ed.), p. 456. Pergamon Press, Oxford, 1063. 

To give a short survey of the characteristic fragmentation patterns of the compounds discussed, the reproduced spectra contain only the key fragments the minor peaks necessary for their identification may be found in the literature. 

Naturally Occurring Furan Derivatives The mass spectra of naturally occurring oxygen heterocyclics were reviewed only recently.52 

The mass spectra of columbin (97) and some closely related compounds have been published and discussed.22b The most prominent cleavage reaction possibly involves a cyclic mechanism in which one molecule of C02 is eliminated and a stable vinylfuran ion is produced, (97)— [98]  

The alternative fragment [99] of mass 220 cannot stabilize the positive charge as well as [98] and is prone to further decomposition. Therefore it is formed in low abundance only. 

---

Nucleophilic substitution of the diazo group is practically the only method for the production of nitro derivatives of tetrazole [392, 436 143], 5-Nitrotetrazole itself was isolated and identified in the form of metallic salts [436-440, 442, 443], The mechanism of substitution of the diazo group by a nitro group in heterocyclic compounds has not been studied specially. As already mentioned, in many cases the reaction takes place as catalytic nucleophilic substitution and does not require the use of a catalyst (copper salts) [392,444], The results from investigation of the kinetics of the substitution of the diazonium group by the nitro group in compounds of the benzene series make it possible to suppose that the diazonitrite is formed intermediately and quickly reacts with a second nitrite anion [392,444], Some difference between the kinetics of the reaction of 3-diazonium-5-carboxy-l,2,4-triazole and 3-diazonium-5-methoxycarbonyl-l,2,4-triazole with sodium nitrite in hydrochloric acid and the analogous process in the benzene series is probably due to prototropic... 

There are three types of nomenclature used for heterocyclic compounds. Many heterocycles have trivial names, which are based on their occurrence, special properties, or historical reasons such as discovery of particular material. Systematic names of heterocyclic compounds derived from the structure of the compound are governed by lUPAC rules, which are divided into two groups the Hantzsch-Widman and replacement nomenclatures. In this book, we were trying to follow the guidelines for naming the heterocyclic compounds, which are summarized in Chapter 2 of the excellent book The Chemistry of Heterocycles Structures, Reactions, and Applications ... 

The theory and practice of the VNS reactirais have been examined in detail by the group of Prof. M. Mgkosza (for reviews, see [14, 18, 20-22, 25, 36, 37]. This well-developed methodology has been extended to many organic reactions, such as direct introduction of alkyl, hydroxy, and amino substituents into electron-deficient arenes (mainly nitroarenes), azines, and nitro derivatives of heteroaromatic compounds. Several excellent reviews dedicated specially to the VNS reactions of heterocyclic compounds have been published [18, 132]. 

Fluorinated Heterocyclic Compounds. HeterocycHc compounds containing the CF group are prepared by methods similar to those used in the fluorination of aHphatic compounds. The direct action of fluorine on uracil yields the cancer chemotherapy agent, 5-fluorouracil [51-21-8] as one special example of a selective fluorination on a commercial scale (25). 

Surprisingly, some 2,3,6-substituted pipecolic acid derivatives like 2 favor exclusively the anti amide isomer [19]. The anti preference of 2 has been demonstrated by NMR spectroscopy in solution (methanol and DMSO) and X-ray analysis in the solid state. The reason for this unexpected finding is the special arrangement of substituents on the pipecolic heterocycle. In contrast to compounds like 1, the additional bulky substituent attached to C3 forces the carboxy group at C2 into an equatorial position and the substituent at C6 into an axial position. 

Methyl isocyanate and all isocyanic acid esters are an interesting and highly reactive class of organic compounds, since the isocyanate group (-NC0) reacts readily with a wide variety of compounds as well as with itself to form dimers, trimers, ureas, and carbodi-imides. Methyl isocyanate (MIC) is an intermediate in the preparation of carbamate pesticides and conceivably could be applied to the production of special heterocyclic polymers and derivatives. 

Reduction of heterocyclic disulfides and anodic reactions of sulfhydryl compounds show no special features. Elimination of a sulfhydryl group may be the slow step in some reactions. 

The special type of carbonyl-group derivatization is aimed for gas chromatography-mass spectrometry (GC-MS) determination of double-bond C = C positions in the unsaturated long-chain acids. The analytical derivatives for the solution of this problem are nitrogen-containing heterocycles. These compounds can be synthesized by condensation of carboxylic acids with 2-amino-2-methyl-l-propanol (2-substituted 4,4-dimethyloxazolines), 2-aminophenol (2-substituted benzoxazoles), and so forth. 

---