Bromides acridizinium

It has been demonstrated (59JA1938) that the attack of phenylmagnesium bromide on acridizinium bromide (3) is at position 6, for oxidation afforded 2-(2-benzoylben-zoyl)pyridine (Scheme 16). 

Sulfonation (66JOC565) or nitration (74JOC1157) of the acridizinium (benzo[Z ]quin-olizinium) ion (3) occurs at position 10 (Scheme 31). When acridizinium bromide is dissolved in liquid bromine and allowed to stand for 15 h the perbromide salt of 7,8,9,10-tetrabromo-7,8,9,10-tetrahydroacridizinium ion is formed and this is easily converted to the simple bromide by the action of acetone. If the tetrabromo salt is refluxed in xylene, it is reconverted to acridizinium bromide (3) in good yield. Treatment of the tetrabromide with sodium acetate gives 10-bromoacridinium bromide (Scheme 32). 

Tab. 2.5.1. Binding constants and binding-site size of acridizinium bromides 5a and 5b as determined from spectrophotometric titrations with st DNA, (poly[dA-dT -poly[dA-dT ), and (po ly[d G-d C]-po ly[d G -d C]).

The hydrogenation of acridizinium bromide (Scheme 26) with a palladium catalyst can be carried out so that only one mole of hydrogen is absorbed to afford a 6,11-dihydroacridizinium salt (68JOC1296). With the same catalyst the hydrogenation of benzo[c]quinolizinium chloride slows after the addition of two moles of hydrogen and gives l,2,3,4-tetrahydrobenzo[c]quinolizinium chloride (71JCS(C)3650). 

On the basis of Monte Carlo simulations [40] and molecular orbital calculations [26a], hydrogen bonding was proposed as the key factor controlling the variation of the acceleration for Diels-Alder reactions in water. Experimental differences of rate acceleration in water-promoted cycloadditions were recently observed [41]. Cycloadditions of cyclopentadiene with acridizinium bromide, acrylonitrile and methyl vinyl ketone were investigated in water and in ethanol for comparison (Scheme 3). Only a modest rate acceleration of 5.3 was found with acridizinium bromide, which was attributed to the absence of hydrogenbonding groups in the reactants. The acceleration factor reaches about 14 with acrylonitrile and 60 with methyl vinyl ketone, which is the best hydrogen-bond acceptor [41]. 

Scheme 3. Kinetics of the cycloaddition between cyclopentadiene and acridizinium bromide...

Irradiation of 3-amino-2-oxo-4-hydroxyquinoline leads to its photochemical condensation to a dimer,and photodimerisation of acridizinium bromide in both solution and in the solid state forms four photodimers, two of which may be enantiomeric. In anionic micelles, a different regioselectivity is observed as reflected in a higher yield of those dimers showing higher dipole moments. 

Contrary to previous reports, acridizinium bromide yields all four isomeric [4+4]photodimerisation products both in solution and in the solid state. 2-Cyano-6,6-dimethyl-2-cyclohexenone undergoes photoaddition to 2,3-dimethyl-2-butene to give tricyclic[c,d]fused isoxazole (146) in 92% yield, possibly involving the triplet biradical (144) and the nitrene (145). With 2-methyI-2-butene and 2-methylpropene, isoxazoles (147) and (148) respectively are formed, though products from competitive formation of triplet biradical (149) are also found.The crystalline 1 2 adducts of 1,2,4,5-tetracyanobenzene with benzyl cyanide yield the coupling product (150) on irradiation this involves electron and proton transfer, radical coupling and tautomerisation steps. In solution (150) is not formed. 

The Diels-Alder reaction between acridizinium bromide and cyclopentadiene is typically catalyzed by cage compounds. In a seminal paper by Otto et al. [18], selection of catalysts was performed using the reaction product as a suitable TSA to select macrocycles from a dynamic library. Exposure of the dynamic combinatorial library (DCLs) based on dithiol building blocks to the product (as TSA) leads to the selection and the amplification of two hosts among all the constituents of the dynamic library (Figure 4.6). The selected cage compounds were applied as catalysts in separate experiments and, indeed, compound 7 was demonstrated to catalyze the Diels-Alder reaction between the two substrates. The reaction rate was... 

When first reported by Bradsher and Solomons in 1957, this reaction represented the first example of a Diels-Alder reaction in which the diene was a quaternary ammonium salt. The reaction of acridizinium bromide with now classical dienophiles, e.g., maleic anhydride, malonate or fumarate esters and acrylonitrile was found to afford the expected Diels-Alder adducts. However, benzoquinone failed to generate any of the predicted products. While the concept of an inverse electron demand Diels-Alder reaction had theoretically been hypothesized much earlier, this was the first practical example of such a reaction. 

Acridizinium salts. A soln. of l-benzyl-2-(l,3-dioxolan-2-yl)pyridinium bromide (prepn. s. 995) in 48%-HBr refluxed 11 hrs. acridizinium bromide. Y 95%.— The cyclic acetal was superior to any known picolinaldehyde derivative in both the yield and quality of the product. F. e. s. G. K. Bradsher and J. G. Parham, J. Org. Ghem. 28,83 (1963) 6a-azonianaphthacenequinones, compounds being quinolizinium salts as well as quinones, s. J. Org. Ghem. 28, 1669. 

As a first example, Sanders, Otto, and coworkers described the isolation of a catalyst for the Diels-Alder reaction between acridizinium bromide (38) and... 

Scheme 9.5 Diels-Alder reaction between acridizinium bromide 38 and cyclopentadiene 39, and macrocycles 41 and 42 self-selected by the product 40.

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