Acridine hydrogenation

Photopolymerization reactions are widely used for printing and photoresist appHcations (55). Spectral sensitization of cationic polymerization has utilized electron transfer from heteroaromatics, ketones, or dyes to initiators like iodonium or sulfonium salts (60). However, sensitized free-radical polymerization has been the main technology of choice (55). Spectral sensitizers over the wavelength region 300—700 nm are effective. AcryUc monomer polymerization, for example, is sensitized by xanthene, thiazine, acridine, cyanine, and merocyanine dyes. The required free-radical formation via these dyes may be achieved by hydrogen atom-transfer, electron-transfer, or exciplex formation with other initiator components of the photopolymer system. 

The results are consistent with the rate-determining step being addition of the aryl radical to the aromatic ring, Eq. (9). Support for this mechanism is derived from the results of three other studies (a) When A -nitrosoacetanilide is decomposed in pyridine, the benzene formed by abstraction of hydrogen from pyridine by phenyl radical accounts for only 1 part in 120 of the reaction leading to phenyl-pyridines. (b) 9,9, 10,lCK-Tetrahydro-10,10 -diphenyl-9,9 -bianthryl is formed in the reaction between phenyl radicals and anthracene, probably by the addition mechanism in Eq. (11). Adducts are also formed in the reactions of benzyl radicals with anthracene- and acridine. ... 

The aromatic spacer group of the model receptors prevent the formation of intramolecular hydrogen bonds between the opposing carboxyls yet these functions are ideally positioned for intermolecular hydrogen bonds of the sort indicated in 32. The acridine derivatives do indeed form stoichiometric complexes with oxalic, malonic (and C-substituted malonic acids) as well as maleic and phthalic acids, Fumaric, succinic or glutaric acids did not form such complexes. Though protonation appears to be a necessary element in the recognition of these diacids, the receptor has more to... 

The reaction network for 5,6-benzoquinoline [101] has been proposed in a more detailed level than that of acridine. In this network, conversely to acridine network, only one primary hydrogenation product, l,2,3,4-tetrahydro-5,6-benzoquinoline, was identified, and in contrast to the quinoline case however, no aniline derivatives were detected. 

Scheme 52 explains the [(Cp )Rh(MeCN)3]2+-assisted regioselective hydrogenation of pyridines, benzoquinolines, acridines as well as indoles and benzothiophene.258 The relative hydrogenation rates were attributed to both electronic and steric effects, the rate generally decreasing with increasing basicity and steric hindrance at the nitrogen atom. 

As a general trend, six-membered mononuclear N-heteroaromatics such as pyridine and derivatives are much less prone to undergo hydrogenation than bi-and trinuclear N-ring compounds (e.g., quinolines, benzoquinolines, acridines) due to their higher resonance stabilization energy. 

Reaction conditions used for reduction of acridine [430,476, partly hydrogenated phenanthridine [477 and benzo f]quinoline [477 are shown in Schemes 38-40. Hydrogenation over platinum oxide in trifluoroacetic acid at 3.5 atm reduced only the carbocyclic rings in acridine and benzo[h]quinoline, leaving the pyridine rings intact [471]. 

Cyclic 1,3-diketones can also participate in this MCR. Thus, utilization of two equivalents of 1,3-cyclohexanedione or dimedone instead of (3-ketoesters led to hydrogenated acridine derivatives. However, when only one equivalent of cyclic 1,3-dicarbonyl is used in combination with one equivalent of (3-ketoester, unsym-metric 1,4-DHPs may be obtained (Scheme 3). For example, this reaction was applied to the synthesis of ZD0947, a potassium chaimel opener [20]. 

Reaction of aldoximes with dimedone derivatives under microwave irradiation leads to partially hydrated acridine derivatives . Eused heterocyclic compounds containing partially hydrogenated pyridine and quinoUne rings were prepared by intramolecular cycloaddition reaction of 5-alkynyl oxime derivatives . (Z)-l,10a-Dihydropyrrolo[l,2-i>]... 

Scheme 4.8 Rebek s trifunctional enolization catalyst including a general base (acridine nitrogen), hydrogen bond donor (carboxylic acid), and a binding group (carboxylate).

Protonated pyridines and derivatives readily undergo acylation at C-2 or C-4 (Table 28) (76MI20503). Acyl radicals are usually generated either by hydrogen abstraction from aldehydes (Scheme 210), or by oxidative decarboxylation of a-keto acids (Scheme 211). In the former case (Scheme 210) with acridine as the substrate, reduction can take place to give a dihydroacridine. 

Benzo ring reduction in acridine can be achieved in a variety of ways. 1,4,5,8-Tetrahydro-acridine is given by lithium in liquid ammonia and ethanol (Scheme 35) (69AJC1105). The symmetrical octahydroacridine (48) can be obtained by hydrogenation of acridine over platinum oxide in trifluoroacetic acid. The product is obtained in quantitative yield (Scheme... 

The hydrogenation of phenanthridine at 250 °C under pressure in the presence of a sodium-rubidium catalyst in benzene is reported to give octahydrophenanthridines. Acridine similarly forms a variety of reduction products (71JOC694). 

Pyridinethiones and thiols are readily oxidized to the corresponding disulfides by reagents such as hydrogen peroxide, potassium ferricyanide and bromine, e.g. Scheme 126 (70JCS(C)1530). Treatment of acridine-9-thione with sulfuric acid gives acrid-9-one. 

An interesting example where erroneous mechanistic conclusions were drawn from sensitization experiments is the photoreduction of acridine (17). Although irradiation of acridine in a variety of hydrogen containing solvents gave measurable reduction to acridan and diacridan, addition of benzophenone or acetophenone greatly enhanced the rate of this reaction.113... 

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