Substitution at nitrogen

Chapter 9. Synthetic Modification of Indoles by Substitution at Nitrogen. 89... 

Unlike alcohols and alkyl halides which are classified as primary secondary or tertiary according to the degree of substitution at the carbon that bears the functional group amines are classified according to their degree of substitution at nitrogen An amine with... 

X-ray analysis of an optically active oxaziridine substituted at nitrogen with the 1-phenylethyl group of known configuration led to the absolute configuration (+)-(2R,3R)-2-(5-l-phenylethyl)-3-(p-bromophenyl)oxaziridine of the dextrorotatory compound as expected, C-aryl and A-alkyl groups were trans to each other (79MI50800). 

Very few 1-unsubstituted 17/-azcpines have been isolated and, as a consequence, substitution at nitrogen is a rare event however, 1-mesyl-l//-azepine (8) and l-(trimethylsilyl)-l //-azepine (9) can be obtained by treating 1//-azepine (7) with mesyl chloride and with trimethylsilyl trifluoromethanesulfonate, respectively.9... 

For substituted anilines (Thompson and Williams, 1977) and for 1-naphthylamine and a series of derivatives thereof (Castro et al., 1986a), k2 and the ratio Ar 2/Ar3 have been determined for nucleophilic catalysis with Cl-, Br-, SCN-, and SC(NH2)2. The values of k2 correspond fairly well to those found for the diazotization of aniline, but those of Ar 2/Ar3 increase markedly in the above sequence (Table 3-1). As k3 is expected to be independent of the presence of Cl- or Br- and to show little dependence on that of SCN- or thiourea, the increase in k 2/k3 for this series must be due mainly to 2. Indeed, the value of log(Ar 2/Ar3) shows a linear correlation with Pearson s nucleophilicity parameter n (Pearson et al., 1968). This parameter is based on nucleophilic substitution of iodine (as I-) in methyl iodide by various nucleophiles. The three investigations on nucleophilic catalysis of diazotization demonstrate that Pearson s criteria for bimolecular nucleophilic substitution at sp3 carbon atoms are also applicable to substitution at nitrogen atoms. 

Imidoyl chlorides substituted at nitrogen (usually with an aryl group) are... 

A-Heteroatom-substituted hydroxamic esters can be expected to have different properties to those displayed by simple hydroxamic esters in two respects. On the one hand, bisheteroatom substitution at nitrogen impacts strongly upon the nitrogen hybridization... 

Solvolysis of urea analogues (200) in aqueous KOH leads to hydrolysis of the amide rather than substitution at nitrogen, in keeping with the poor leaving capacity of alkox-ide (equation 28). This reaction is an excellent source of Af,Af-dialkoxyamines (203), a relatively little known class of compounds . 

Amides substituted at nitrogen with both a sulfur and oxygen have only been generated as reactive intermediates. Sulfur is less electronegative than nitrogen and its role in anomeric substitution at nitrogen should be radically different. 

From Table 7 it may be seen that the y-carbon resonance is at a high field for the AA-oxide compared to the corresponding values for pyridine and pyridinium, providing the solvent is non-protonating. This points to shielding due to participation of canonical form (64), which is lost on protonation. Similar effects for a-C are also present, but as expected, are tempered by the proximity variation of substitution at nitrogen,... 

Hexamethyleneimine and its benzo derivatives are typical secondary amines and undergo electrophilic substitution at nitrogen, e.g. alkylation and acylation, under standard conditions. Most form stable hydrochlorides and simple derivatives such as picrates (B-67MI51600). Table 4 contains pjRTa values of some azepines. 

The NH protons of diamine and triamine complexes of gold(IH) are acidic, as shown by the data in Table 12. The acidity increases with the degree of substitution at nitrogen, and the trend is attributed primarily to steric effects.589-591... 

High enantioselectivity (ca. 95-99% ee) is observed in this system, better than that revealed in previous reports of the hydrosilylation of imines. The mechanism is as yet unclear however, the authors propose that an active catalyst may be formed by cleavage of the Ti-F bond and generation of a Ti(III) hydride species. Insertion of an imine into the Ti-H bond, followed by a (r-bond metathesis with the silane in a four-centered transition state, may lead to the observed products. Another report on the activity of titanocene complexes as catalysts for the hydrosilylation of aid- and keti-mines also indicates formation of a Ti-H species as catalyst.188 Hydrosilylation proceeds to yield silylamines, with dependence on substitution at nitrogen and on the nature of the ligand bound to the metallocene precursor. 

The physical properties of amines depend in an important way on the extent of substitution at nitrogen. Thus primary amines, RNH2, and secondary amines, R2NH, are less volatile than hydrocarbons of similar size, weight, and shape, as the following examples show ... 

Electrophilic substitution at nitrogen can occur in either ring, and the preference may depend on the nature of the substituents. Electrophilic substitution at carbon proceeds readily in the presence of electron-releasing substituents. 

Electrophilic substitution at nitrogen can occur in either ring depending on the nature of the substituents present. Electrophilic substitution at carbon proceeds readily in the presence of electron-releasing substituents. A wide variety of electrophiles have been studied. Mesoionic systems are readily substituted and cationic structures may become very reactive when conditions are chosen so as to promote intermediate formation of a pseudo-or anhydro-base. Sulfoxides are formed in the peracid oxidation of fused dihydrothiazoles. 

The synthesis of vinyl sulfoximines via the elimination reactions of P-hydroxy sulfoximines11,12,33,72,78 has been discussed in Section TV. A. The method of Craig33 is particularly useful for the preparation of N-unsubstituted vinyl sulfoximines 210 which can be readily substituted at nitrogen by reactions with a number of reagents (see Section II.A) including trifluoromethane sulfonic anhydride (triflic anhydride).33... 

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