Salts nitrilium

Detailed mechanistic studies by Fodor demonstrated the intermediacy of both imidoyl chlorides (6) and nitrilium salts (7) in Bischler-Napieralski reactions promoted by a variety of reagents such as PCI5, POCI3, and SOCh)/ For example, amide 1 reacts with POCI3 to afford imidoyl chloride 6. Upon heating, intermediate 6 is converted to nitrilium salt 7, which undergoes intramolecular electrophilic aromatic substitution to afford the dihydroisoquinoline 2. Fodor s studies showed that the imidoyl chloride and nitrilium salt intermediates could be generated under mild conditions and characterized spectroscopically. Fodor also found that the cyclization of the imidoyl chlorides is accelerated by the addition of Lewis acids (SnCU, ZnCh), which provides further evidence to support the intermediacy of nitrilium salts. ... 

Side reactions consistent with decomposition of intermediate nitrilium salt 7 have also been observed, including retro-Ritter reactions that afford alkenes (8), and VonBraun reactions that provide alkyl chlorides (9). ... 

In some instances the attack of the arene on the nitrilium salt occurs at the ipso carbon rather than the ortho carbon. For example, the Bischler-Napieralski cyclization of phenethyl amide 10 affords a 2 1 mixture of regioisomeric products 11 and 12. The formation of 12 presumably results from attack of the ipso aromatic carbon on the nitrilium salt 13 followed by rearrangement of the spirocyclic carbocation 14 to afford 15, which upon loss of a proton vields product 12. ... 

Diphenyl-1//-1,2,4-benzotriazepines 3 are formed in good yield by the cydization of the nitrilium salts 2, which in turn are prepared from the benzenehydrazonyl chloride 1 and nitriles... 

Since nitrilium salts can be prepared by treatment of nitriles with trialkyloxonium salts (see 16-8), this is a method for the conversion of nitriles to secondary amines. 

Nitrilium salts, e.g., 66, prepared from the alkylation of nitriles, react with sodium azide to yield 1,5-disubstituted tetrazoles, e.g., 67 (Scheme 7).121 The Schmidt reaction,122 a versatile method for the preparation of 1,5-disubstituted tetrazoles from ketones and hydrazoic acid, can now be regarded as a special case of azide addition to nitrilium salts.123... 

Nitrilium salts (66) react with alkyl or aryl azides to give good yields of 1,4,5-trisubstituted tetrazolium salts (115) (Eq. 20).189,255... 

Dealkylation of related salt 145b, which is stable up to — 20 °C, led to the formation of a nitrilium salt 146. The latter was transformed to amide 147 upon hydrolysis (see Equation 42) <1995HAC559>. 

The reaction of nitrile oxides with nitrilium salts, which are more reactive than the corresponding nitriles, as discussed in CHEC-II(1996) <1996CHEC-II(4)179>, is the main route through to oxadiazolium salts. Further advances in this area have not been reported. 

In the case of the most reactive compounds, substitution at the carbon atom of diselenonium and ditelluronium dications is also a possible pathway. For example, formation of diselenide 117 from selenoxide 115 was explained by demethylation of intermediate dication 116 with trifluoroacetate anion.126 Dealkylation of salt 118, which is stable up to —20°C, leads to formation of nitrilium salt 119. The latter is transformed to amide 120 upon hydrolysis.64 Dealkylation of intermediate diselenonium dication 122 was suggested as the key step in the oxidative synthesis of 1,2,4-diselenazolidines 123 from eight-membered heterocycles 121 (Scheme 46).127... 

Perhaps the earliest examples of a polar cycloaddition are some involving nitrilium salts. Meerwein et al. found that A -arylacylimido chlorides (70) in the presence of Lewis acids (usually added in the form... 

An alternative method of generating nitrilium salts for a cycloaddition reaction is by the decomposition of an aryldiazonium fiuoroborate (80) in the presence of a suitable nitrile. This method has the disadvantage... 

Nitrilium salts are more reactive 1,3-dipolarophiles than nitriles. With stable nitrile oxides, oxadiazolium salts (228) are obtained (Equation (38)). With unstable nitrile oxides the cycloaddition... 

The reactions of nitrilium salts with nitrones usually give tars. However, pyridine-A -oxides afford oxazolium salts, which rearrange in solution to more stable amides (Scheme 105) <71TL1947,75JOC4l>. 

Treatment of N-oxides with imidoyl chlorides or nitrilium salts can lead to intramolecular amination. This is a useful direct method for the introduction of a 2-arylamino group into the pyridine ring (Scheme 99) (74JOC1795). The by-products that are isolated in some of these reactions are believed to be formed as shown. When the a-positions are blocked a... 

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