10- Methyl-9- acridinium cations

The selectivity toward the hydride transfer from the 4 position of these compounds was also studied for the reduction of 10-methyl-acridinium cation with 38-4- , 39-4-d, and 40-4-d that were prepared by the reduction of 43, 44, and 45 with BNAH-4,4-d2, respectively. 

An example of disproportionation to (109) and (110) is provided by the behaviour of the berberinium ion in alkaline solution (Scheme 62). The pseudobase of the 5-methyl-phenanthridinium cation is present even in neutral solution (equation 85). Attack at position 9 in acridinium salts is also very easy, and they rearrange to pseudobases in a few minutes in alkaline solution. These pseudobases, unlike the others described, do not undergo ring opening. They readily disproportionate or are oxidized to acridin-9-ones by air when the starting salt is unsubstituted at C-9 (B-78MI20502). Pyridine 1-oxides and their analogues... 

Various other miscellaneous salts have been used from time to time to initiate cationic polymerisation. These include tris-p-bromophenyl aminium hexa-chloroantimonate (97), anilinium hexafluoroantimonate (98), nitronium tetra-fluoroborate (95), thianthrenium perchlorate (99), and hexachloroantimonate (100), and N-methyl acridinium and N-methylphenazonium salts (75). In general... 

Further benzologation leads to measurable pvalues for the IV-methyl-acridinium (9.8626) and N-methylphenanthridinium (11.9441) cations however, pKR+ > 14 in aqueous solutions of the N-methyl cations of both the 5, 6- and 7, 8-benzoquinolines.41 The loss in resonance energy upon pseudobase formation is expected to be one of the major factors involved in considerations of the relative susceptibilities of heterocyclic cations to pseudobase formation. A rather crude, but informative, calculation of the loss in resonance energy (AR) upon pseudobase formation has been attempted for each of the above cations. 

This tendency to pseudo-base formation increases with the complexity of the heterocyclic nucleus. Thus, whereas pseudo-base formation does not occur for the i-methylpyridinium cation, and only at a very high pH for the i-methylquinolinium and 2-methylisoquinolinium ions, the reaction takes place much more readily upon further annelation (as in lo-methyl-acridinium). The insertion of an electron-attracting substituent (such as -NOg), or a second doubly-bound ring-nitrogen atom, as in quinox-alinium and quinazolinium, has the same effect. Some examples are listed in Table 10.5, in which p/Crqh is the pH at which the pseudo-base and the quaternary cation are present in equal concentrations. Formally p/Croh is similar to a piCa value, but the equilibrium is only slowly achieved. 

Figure 3.30 Structure of ABPAC, a 9-aryl, 10-methyl derivative of the acrdinium cation, where the aryl group is 4 -amino-4-biphenylyl. The dihedral angles associated with the single bonds linking the phenyl groups are labeled 03 (phenyl/acridinium) and 02 (the biphenylyl moiety), with zero defined by coplanarity (as drawn). For the aminophenyl linkage (NC), 01 refers to the dihedral angle between the HNC and NCC planes associated with the HNCC bonded sequence. The optimized H2N moiety is pyramidalized, and is nearly symmetrically disposed with respect to the mean plane of the attached phenyl group (with 01 = 17°) [29].

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