The Nitrogen Analogs

The possible nitrogen analogs of carbonium ions are the cation LIII and its conjugate base LIV. 

The simplest intermediate of the nitrogen cation type is the nitronium ion, the active species in most aromatic nitration reactions. There is both cryoscopic and spectroscopic (Raman and infrared) evidence for its existence.802 On the other hand, it has a structure with quaternary rather than electron deficient nitrogen, a structure compatible with the centrosymmetric geometry demanded by the spectra. The Raman line at 1400 cm.-1 has been assigned to the totally symmetric vibration of the linear triatomic molecule. 

The Schmidt reaction of ketones with hydrazoic acid is believed to be a similar rearrangement, again with concerted trans migration and elimination of nitrogen. 

When the two groups of the ketone are para-substituted phenyls, the product of the Schmidt reaction is usually a nearly equimolecular mixture of the two isomeric amides.806 This result, obtained instead of a preferential migration of the more electron-releasing group, is consistent with a mechanism in which the formation of the intermediate rather than its rearrangement is rate determining. 

In the reaction of hydrazoic acid with carboxylic acids the amine is probably formed by way of an intermediate identical with that 

---

There are four types of organic species in which a carbon atom has a valence of only 2 or 3/ They are usually very short lived, and most exist only as intermediates that are quickly converted to more stable molecules. However, some are more stable than others and fairly stable examples have been prepared of three of the four types. The four types of species are carhocations (A), free radicals (B), carbanions (C), and carbenes (D). Of the four, only carbanions have a complete octet around the carbon. There are many other organic ions and radicals with charges and unpaired electrons on atoms other than carbon, but we will discuss only nitrenes (E), the nitrogen analogs of carbenes. 

Nitrenes (R—N) are the nitrogen analogs of carbenes, and most of what we have said about carbenes also applies to them. Nitrenes are too reactive for isolation under ordinary conditions, although ab initio calculations show that nitrenes are more stable than carbenes with an enthalpy difference of 25-26kcal moP... 

At least two types of nitrenium ions, the nitrogen analogs of carbocations, can exist as intermediates, though much less work has been done in this area than on carbocations. In one type (46), the nitrogen is bonded to two atoms and in the other... 

The Nitrogen Analogs of Enols and Enolates Enamines and Imine Anions... 

The nitrogen analogs of ketones and aldehydes are called imines, azomethines, or Schiff bases, but imine is the preferred name and we use it here. These compounds can be prepared by condensation of primary amines with ketones or aldehydes.102 The equilibrium constants are unfavorable, so the reaction is usually driven forward by removal of water. 

Imines can be deprotonated at the a-carbon by strong bases to give the nitrogen analogs of enolates. Originally, Grignard reagents were used for deprotonation but lithium amides are now usually employed. These anions, referred to as imine anions... 

The nitrogen analogs of carbenes are called nitrenes. As with carbenes, both singlet and triplet electronic states are possible. 

Compounds 17 were formed by the reaction of Is(R)SiF2 (R = Is, /Bu) with two equivalents of [LiPH2(DME)] (DME = 1,2-dimethoxyethane). They do not show any tendency to eliminate LiF in THF solutions, surely because of the strong Si—F bond. Similar stability was observed for the nitrogen analogs.13... 

Hydrazine has the structure H2N-NH2, and it is the nitrogen analog of hydrogen peroxide, HO-OH. Although hydrazine is unstable (the heat of formation is +50kJ/mol), it reacts as a weak diprotic base... 

Radicals in which the odd electron is on a nitrogen next to an aromatic ring are stabilized by resonance analogous to that of tri-phenylmethyl. In the case of Wurster s salts, the nitrogen analogs of semiquinones, there are two equivalent resonance structures in the acid form, but in the less stable basic form one of the structures requires separation of charge. Evidence for the unpaired electron has been obtained by measurement of the paramagnetism.144... 

Nitrenes, the nitrogen analogs of carbenes, are too reactive for isolation under ordinary conditions. The ground state of NH, and of most nitrenes, is a triplet. Aryl nitrenes have been trapped at 77 K,186 the more reactive alkyl nitrenes in matrices at 4 K.187... 

The aziridines are the nitrogen analogs of the epoxides and undergo similar electrophilic reactions. No biological data were obtained for these compounds nor were they used as precursors to any CA-4, 7, analogs. They have been included since the synthesis is noteworthy, and they could be interesting intermediates. Xu et al. stereoselectively aziridinated chalcones using the nitrene precursor (PhINTS) and a copper catalyst to form compound 141 (Scheme 36) [82],... 

Related work had shown that the nitrogen analogs of the cyclic ketene acetals were readily synthesized and would polymerize with essentially 100% ring opening. For this reason their copolymerization with a variety of monomers was undertaken (6). 

In addition to sulfimides, the nitrogen analogs of sulfinates and sulfinamides are chiral and have been obtained as optically active compounds. For instance, the synthesis of diastereomeric menthyl p-toluenesulfinimidoates 90 mentioned above was effected by Cram and his collaborators (18,137) on two ways. The first comprised the reaction of racemic A -tosyl-p-tolueneiminosulfinyl chloride 92 with menthol, followed by separation of the diastereomers of 90, whereas in the second method the reaction of the ester (->45 with chloramine T was utilized. 

Pyrazinamide was synthesized in 1952, and it is the nitrogen-analog of nicotinamide. It exhibits hepatotoxicity. Synonyms of this drug are dexambutol, miambutol, esnbutol, ebu-tol, and others. 

SECTION 1.9. THE NITROGEN ANALOGS OF ENOLS AND ENOLATES— ENAMINES AND IMINE ANIONS... 

The nitrogen analogs of carbenes are called nitrenes. As with carbenes, both singlet and triplet electronic states are possible. The triplet state is usually the ground state for simple structures, but either species can be involved in reactions. The most common... 

Wittig and Blumenthal [1] in 1927 introduced the term enamine to designate the nitrogen analog of the term enol (structures I and II). The enamine... 

It was then reasoned that reactions of enantiopure propargylic amines should lead to the nitrogen analogs of 96 in non-racemic form52. First, the de was optimized using racemic starting material 97 (equation 46 and Table 11, entries 1-4)52. 

In the fused benzofuran series, the same method, applied to bromoacyl-o-hydroxycoumarins502,549 and bromoacyl-o-hydroxyxan-thones321,433,550 allows the synthesis of the corresponding oxo-dihydrofuro derivatives. The nitrogenated analogs of compounds 237 (2,3-dihydro-3-oxofuro[2,3-6] and -furo[3,2-c] pyridines) have also been obtained.551,552... 

As early as 1964, polycyclic aromatic hydrocarbons (PAHs) known to be carcinogenic, such as benzo[a]pyrcne, were detected in broiled meat (164). A number of papers have been published about PAHs found in smoked and thermally treated foods as a result of pyrolysis or incomplete combustion of organic matter (165 -169). Less information is available on the nitrogen analogs, the basic azaarenes polycyclic aromatic nitrogen-containing hydrocarbons (PANHs), but they have been shown to be present in association with PAHs in various samples that contain nitrogen, such as processed food (170-172). 

The dithioester 83, which can be written as an ylid (84), with DMAD alone at 100°, gave 10% of 85.287 The nitrogen analog 86 apparently... 

---