1,2-Dihydroacridines

Acridine (9) combines readily with dimethyl acetylenedicarboxylate in methanol yielding the methoxide (11), which is in equilibrium with the corresponding 9-methoxy-9,10-dihydroacridine (12). Presumably the first formed zwitterion (10) abstracts a proton from the solvent,... 

Dibenz[6,/ azepines 36 from 9,10-Dihydroacridines 35 General Procedure 30... 

Method A To a mixture of the 9-(hydroxymethyl)-9,10-dihydroacridine (4mmol) and sea sand (10g) under N2 in refluxing anhyd xylene (30 mL) was added in four portions during a 2-h period, P205 (4g, 28 mmol). The yellow-orange mixture was heated under reflux for an additional 1.5 h, then cooled, and quenched cautiously with a large excess of cold H20. The mixture was filtered to remove the sand, and the aqueous layer was then separated from the filtrate. The sand and the aqueous layer were extracted with hot benzene and the benzene and xylene solutions were combined, dried, and the solvent removed under reduced pressure. The crude product was obtained as a yellow-orange residue which was purified by crystallization (benzene). 

Dihydroacridine-10-carbaldehyde (4) is the major product (57%) from the oxidation of 1 l//-dibenz[7),e]azepine (3) with peracetic acid.222 1 l//-Dibenz[/),e,]azcpin-6(5/7)-one (5) is also formed along with trace amounts ( < 4 %) of 9-acridone-10-carbaldehydeand 5,6-dihydro-l 1H-dibenz[ >,< ]azepine-6,l 1-dionc. 

The reduction of acridine to 9,10-dihydroacridine by the precursor [RuH(CO) (NCMe)2(PPh3)2]BF4 has been found to occur with the experimental rate law r=kcat [Ru][H2] and the postulated mechanism involves, as the determining... 

Photoinduced electron transfer [22] from reductants such as l-benzyl-l,4-di-hydronicontinamide [27], the Hantzsch-ester [22] (diethyl-2,6-dimethyl-l,4-di-hydropyridine-3,5-dicarboxylate) or 10-methyl-9,10-dihydroacridine [27, 28] to the fullerene and successive proton transfer leads selectively to l,2-dihydro[60]fullerene. These reductions usually proceed under mild conditions. 

Substitution of the nine position is a common transformation for acridines. An optimized method for preparing the 9-carboxamides uses BOP/DMF <99SC4341>. Reaction of 9-isothioacridines with the sodium anion of diethylmalonate is followed by alkylation with bromoacetate to afford the spiro[dihydroacridine-9(10i/)-thiazolidines] <99H(51)137>. 

Pyridine reacts with sodium hydrazide in the presence of hydrazine to yield 2-hydrazinopyridine in the absence of free hydrazine a hydrazo compound is formed (Scheme 88) (64AG(E)342). A difference between hydrazination and amination is the formation of 1,4-adducts which cannot be rearomatized even on heating. This is reflected in the behaviour of quinoline, which gives only a 0.5% yield of a -hydrazino product, whereas 4-methylquino-line is hydrazinated in 76% yield (64AG(E)342). Acridine behaves differently with sodium hydrazide/hydrazine, 9,10-dihydroacridine is formed almost quantitatively, but reaction in the absence of hydrazine yields 9-aminoacridine (65%). An even higher yield of 9-amino-acridine is obtained when sodium Af.AC-dimethylhydrazide is used (Scheme 89). Good evidence for intermediacy of (151) comes from the isolation of (152) on hydrolysis of (151). 

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. 

Ring expansion of more readily accessible acridines provides an alternate method for preparing the dibenzazepines. The starting halide (18-1) can be obtained by chlorination of the corresponding A -acetyl dihydroacridine. The displacement of... 

Anodic oxidation of 9,9-substituted 9,10-dihydroacridines in CH3CN-Bu4NC104 at a Pt electrode gives a cation-radical that dimerizes to a 2,2 -biacridine system such a dimer is further oxidizable to a quinonoid... 

Reductions with noble metal catalysts proceed smoothly (at 20°C) when the bases are in the form of hydrochlorides the free bases tend to poison the catalyst. A pyridine ring is reduced more easily than a benzene ring thus, 2-phenylpyridine gives 2-phenylpiperidine (384), quinoline gives 1,2,3,4-tetrahydroquinoline (385) and acridine gives 9,10-dihydroacridine (386). 

Dihydroacridines carbazoles.3 Addition of 2-azidodiphenylmethane (1) to a suspension of A1C13 in CH2C12 results in liberation of N2 and formation of 9,10-dihydroacridine (2). A similar reaction with 2-azidobiphenyl results in carbazole (83% yield). 

It has been demonstrated that visible light irradiation of the absorption band of AcrH + in the presence of organometallic compounds and alkenes and alkylbenzenes in MeCN results in efficient C-C bond formation between these electron donors and AcrH+ via photoinduced electron transfer from the donors to the singlet excited state of AcrH+ to yield the alkylated or allylated adducts selectively [89-91], The AcrH+ is also photoreduced by ethylbenzene and other alkylbenzenes to yield the corresponding 9-substituted-10-methyl-9,10-dihydroacridine [92] ... 

Photo-induced H-abstraction of anthraquinone from xanthene has been studied using nuclear polarization-detected EPR and the structure of the resulting short-lived radical pair determined.194 The retrodisproportionation reactions of a variety of styrenes with 9,10-diliydroanthracene (DHA), xanthene (XAN), and 9,10-dihydroacridine (DHAc) have been studied in order to determine if there was any evidence of the alternative hydride-transfer mechanism in competition with the proposed H-atom-transfer mechanism. No such evidence was found.195 The reaction between azulene and DHAC... 

Analogously, acridine (152) is silylated and the resulting 9,10-bis(TMS)-9,10-dihydroacridine (153) is then acylated to 10-acetyl-9-TMS-9-10-dihydroacridine (154) and 10-acetyl-9,10-di-hydroacridine (156), respectively105). 

If 153 plus the acylating agent is only heated briefly (1 h), 154 is not obtained, but 9-TMS-9,10-dihydroacridine (155) instead. Further treatment with the acylating agent leads to 154. Recent developments, especially in France, revealed a broad spectrum of applications14b) using predominantly the two systems TMS-C1 (742)/Li/THF or 142/Mg/HMPT. 

Fukuzumi S, Suenobu T, Kawamura S, Shida A, Mikami K (1997) Selective two-electron reduction of C60 by 10-methyl-9,10-dihydroacridine via photoinduced electron transfer. Chem Commun 291-292... 

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