Attack on Nitrogen

Attack on Nitrogen. The kinetics of the reaction of diazonium salts with dimethyl phosphonate have been studied. The almost third-order behaviour supports the mechanism shown, involving a phosphonate anion rather than a 

The betaine (47), derived from the reaction of tris(dimethylamino)phosphine and dialkyl azodicarboxylate, has been used to prepare monosaccharide 

Attack on Nitrogen. A variety of cyclic derivatives of phosphorous acid have been converted into spirophosphoranes (51), using diethyl azodicarboxylate as the condensing agent,42 probably by initial addition to nitrogen to give (50). Several 

Attack on Nitrogen. Imidophosphoranes have been obtained from the reactions of both phosphorous esters and amides with azides. 2-AJkyl-benzoxazoles are the products from the exothermic reaction of the aryl azide (77) with triethyl phosphite. The intermediacy of the imide (78) was supported by u.v. and n.m.r. spectra of the reaction mixture and confirmed by its isolation as a yellow oil from the reaction at 0 °C in hexane. 

Substituted benzamidoximes react with tris(dimethylainino)phosphine to give 3,4-benzo-l,2-azaphosphole 2-oxides (79). 

Aminophosphines and amidoximes are reported to form the phos-phoramide derivative (63) however, a similar reaction with amidoxime ethers gives the diazadiphosphetidine (64).  

The reaction of dialkyl and trialkyl phosphites with / -quinonedisul-phonimides (65) has evoked considerable interest. Levy and Sprecher isolated the nitrogen phosphorylated product (66) in 80% yield from a reaction with dialkyl phosphite, although other workers claim that attack is at carbon to give (67). 

---

Acylations were often carried out with diaziridines. Twofold acylation is normally observed when two NH groups are present. Most acylations were performed with benzoyl chloride, acetyl chloride or phenyl isocyanate (B-67MI50800). Ring opening reactions during acylation, foreseeable for intermediates of electrophilic attack on nitrogen, were observed only seldom, provided mild conditions were used. 

The nitrogen atoms in ADC compounds are highly electrophilic. Nucleophilic attack on nitrogen is easy, and as with electrophilic acetylenes, such as dimethyl acetylenedicarboxylate, it seems likely that some cycloaddition reactions of ADC compounds with unsymmetrical substrates proceed via a stepwise mechanism. PTAD is a powerful electrophile, although TCNE is more reactive, and chlorosulfonyl isocyanate is more reactive still.58... 

In addition to those methods described in CHEC(1984) and CHEC-II(1996) (primarily alkylation and acylation reactions), Vicentini <1996T7179> has shown that 5-methylimidazo[4,5-f]pyrazole 28 can undergo electrophilic attack on nitrogen by hydroxylamine 0-sulfonic acid to yield the 4-amino species 29 (Equation 1). 

There have been a number of reports of improved selectivity with sulfonic acid resin catalysts compared with conventional liquid acid catalysts[6—9]. Various explanations have also been proposed. If mechanisms usually postulated for condensation reactions with liquid Br0nsted acid [10] and solid acid catalysts [11] are adopted, the sequence of steps shown in Fig. 2 could be considered for the condensation of MFC. Both mechanisms incorporate the essential features of known carbenium ion chemistry, i.t., electrophilic attack on the aromatic ring by polar carbenium ion intermediates. Note that MDU is formed by this attack on the benzene ring of MPC, while the N—benzyl compound by the attack on nitrogen atom. 

An intramolecular reaction, which could be viewed as an electrophilic attack on nitrogen, is mentioned under the reactions of the carbocyclic ring (see Section 7.21.6.1.3) <83CPB1518>. The dihydrobenzodipyrrole (45) was acylated on the pyrrolidine nitrogen atom (87CC1406). The oxidation of some benzodipyrroles, e.g. compound (6), and related tripyrroles, to their JV-oxides can be viewed as an electrophilic attack on nitrogen. 

The primary site of attack in the reactions of the 1,2,5-thiadiazoles and selenadiazoles with lithium alkyls or Grignard reagents is usually at the ring sulfur or selenium (Scheme 2, path A) but attack on nitrogen (path B) or the ring carbon (path C) also occurs. yV-Phenyl-o-phenylenediamine is produced in the reaction of (1) and (2) with phenyllithium, probably via path B (55JCS1468). The driving force for this mode of addition could depend on the stable benzenoid character of the addition intermediate. 

A. Reactivity of Ring Atoms 1. Electrophilic Attack on Nitrogen... 

Attack on Nitrogen. A new route to phosphoramidates, involving the reaction of silyl phosphites with the appropriate azide, followed by hydrolysis, has been developed. The mechanism (see Scheme 6) probably involves initial formation of the phosphite imine (36) followed by migration of a sUyl group from oxygen to nitrogen, and it is exemplified by the synthesis of the oligoazanucleotide (37). 

Attack on nitrogen in neighboring rings occurs in low yield (2-5%)and is accompanied by loss of sulfur (Eq. 87).347... 

---