Nitrilium cation

The miniaturized conditions provided a suitable setting for this reaction, affording several important benefits. First, in microreactor environment this highly exothermic process demanded no additional cooling, whereas the reaction in batch needs to be conducted at 0°C. In addition to this, instant TOF-MS analysis proved the formation of the nitrilium cation intermediate, thus proving the reaction mechanism that was speculative until then. Another advantage of the reactor directly connected to the analyzer is the convenience and the speed of the reaction optimization. 

Scheme 13). A possible mechanistic pathway involves imidoyl chloride and nitrilium cation intermediates. A similar reaction of A.A/ -diacetyl-1,2-diaminobenzene and phosphoryl chloride with the 2,2 -diindolyl-methane 12 did form the macrocycle 46, but only in a very low yield12 (Scheme 13). 

Some of the species most closely related to vinyl cations will be briefly considered. These are the propargyl cations and some isoelectronic analogues of vinyl cations, such as acyl cations, nitrilium cations and the imminium ions. 

Trapping the nitrilium cation is also possible. The most famous example is probably the heterocycle (an oxazine, Chapter 42) produced by intramolecular capture of the nitrilium ion with a hydrox-... 

Alkenes and alcohols condense with nitriles under drastic acidic conditions. In most cases sulfuric acid is used either neat or with solvents such as acetic acid. In liquid hydrogen fluoride containing defined amounts of water, nitriles react with linear or branched alkenes to form amides in good yields. Treatment of allylsilanes and allylstannanes with thallium(III) salts in acetonitrile activates Ae alkene for nucleophilic attack of the nitrile group. The generated nitrilium cation (equation 23) is hydrolyzed to the corresponding )V-allylamide. ... 

Further studies on the behaviour of aliphatic amides in refluxing HMPT suggest that the initial intermediate is the nitrilium cation (36), whose sub-... 

In a new kind of process, iV-allylskatole reacts with a nitrile and a palladium acetonitrile complex to give a palladium complex of proposed structure (51), presumably via intramolecular acylation of the nitrilium cation (50). The complex (51) can be converted into the pyrazinoindole (52) by reaction with benzylamine or the tetrahydro analog (53) with sodium borohydride (Scheme 14) <86JA6224>. Acylation has been effected at C-7 in some 4,6-dimethoxyindoles <94ti(M97>. 

Alkyl arylacetates react with Tf20 to give a cation which in the presence of a nitrile affords isoquinoline derivatives via cychza-tion of the intermediate nitrilium cation (eq 27). ... 

It is commonly assumed that the reaction involves an initial protonation at the oxygen atom of the oxime moiety, giving an oxonium cation, and is followed by the migration of an alkyl group plus the departure of a water molecule to give the nitrilium cation. The latter ion is, in turn, hydrolyzed in a basic solution to finally yield an amide. The mechanism is illustrated below. 

In the absence of moisture cation 25 is stable over a period of weeks, 5, however, decomposes slowly at room temperature to non-identified produets [14-16]. Both cations 5 and 25 show distinct behaviour towards nucleophilic solvents. While their Si-NMR and C-NMR resonances are not influeneed by arene solvents, the addition of the higher nucleophilic acetonitril as cosolvent leads to the formation of silylated nitrilium cations 26 and 27 (Scheme 8). They are characterized by their Si and C chemical shifts (see Figs. 6 and 7) [14, 16]. The silicon resonances are high field shifted by ca 51-56 ppm and similarely, the signals of the vinylic carbon atoms are shifted by 20 ppm to higher field in the NMR spectra of the nitrilium ions. This clearly indicates the breakdown of the intramolecular stabilization of the positively charged silicon center on the expense of intermolecular interactions between the silyl cations and acetonitril. 

It is relevant to point out that Fodor and co-workers have shown that nitrilium cations are intermediates in the Bischler-Napieralski cyclization whenever secondary amides are used. A nitrilium ion was trapped as its crystalline hexafluoroantimonate salt. ... 

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