Carbazole dicarboxylic

Beccalli et al. reported a synthesis of carbazomycin B (261) by a Diels-Alder cycloaddition using the 3-vinylindole 831 as diene, analogous to Pindur s synthesis of 4-deoxycarbazomycin B (619). The required 3-vinylindole, (Z)-ethyl 3-[(l-ethoxy-carbonyloxy-2-methoxy)ethenyl]-2-(ethoxy-carbonyloxy)indole-l-carboxylate (831), was synthesized starting from indol-2(3H)one (830) (620). The Diels-Alder reaction of the diene 831 with dimethyl acetylene dicarboxylate (DMAD) (535) gave the tetrasubstituted carbazole 832. Compound 832 was transformed to the acid 833 by alkaline hydrolysis. Finally, reduction of 833 with Red-Al afforded carbazomycin B (261) (621) (Scheme 5.99). 

Two years later, the same group reported a formal synthesis of ellipticine (228) using 6-benzyl-6H-pyrido[4,3-f>]carbazole-5,ll-quinone (6-benzylellipticine quinone) (1241) as intermediate (716). The optimized conditions, reaction of 1.2 equivalents of 3-bromo-4-lithiopyridine (1238) with M-benzylindole-2,3-dicarboxylic anhydride (852) at —96°C, led regioselectively to the 2-acylindole-3-carboxylic acid 1233 in 42% yield. Compound 1233 was converted to the corresponding amide 1239 by treatment with oxalyl chloride, followed by diethylamine. The ketone 1239 was reduced to the corresponding alcohol 1240 by reaction with sodium borohydride. Reaction of the alcohol 1240 with f-butyllithium led to the desired 6-benzylellipticine quinone (1241), along with a debrominated alcohol 1242, in 40% and 19% yield, respectively. 6-Benzylellipticine quinone (1241) was transformed to 6-benzylellipticine (1243) in 38% yield by treatment with methyllithium, then hydroiodic acid, followed... 

Carbazole-containing PODs have been obtained (53) by cyclodehydration (in the presence of POCl3) of polyhydrazides prepared by polycondensation of IV-ethyl-3,6-carbaZoledicarbonyl chloride with dihydrazides of the corresponding dicarboxylic acids. Thermal decomposition of the polymers containing aliphatic units occurs at 365-380°C, compared to 400-405°C for polymers containing aromatic units. 

The Lewis acid-catalyzed amidation of 9-ethyl-9//-carbazole gave 9//-carbazole-3,6-dicarboxamide 1214 that was saponified to carbazole-3,6-dicarboxylic acid 1215, followed by conversion into carbazole-3,6-dicarbonyl dichloride 1216, utilizing SOCb (Scheme 234) <1997CM1578, 1999SM(99)181>. 

Snyder and co-workers tried to utilize cycloadditions of dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate 150 to N-substituted indoles 325 as the key step in the attempted preparation of carbazoles <1997TL8611>. However, unlike previous examples reported by Haider and Wanko with 3,6-bis(trifluoromethyl)-l,2,4,5-tetrazine 147 <1994ACO205, 1994H(38)1805>, the initially formed dimethyl 5//-pyridazino[4,5-3]indole-l,4-dicarboxylates 326 did not react further with any dienophile. On the other hand, they underwent reductive ring contraction readily with zinc in acetic acid to furnish dimethyl 5//-pyridazino[4,5-3]indole-l,4-dicarboxylates 327 (Scheme 78) <1997TL8611>. 

Copolymers having the carbazole group and the oxadiazole group directly in the backbone, i.e., poly[3,6-A-Ethylcarbazole-l,3,4-oxadiaz-ole-2,5-diyl], can be prepared from A-ethylcarbazole-3,6-dicarboxylic acid and hydrazine hydrochloride.The reaction runs at 140°C with PPA. The synthesis is shown in Figure 10.4. 

Kreher improved upon Welch s lactam reduction by using diisobutylaluminum hydride (DIBAL) to reduce either lactam (Scheme 14, equation 1) [80]. Srinivasan and Jeevanandam employed a route similar to Sha s [78] to prepare a series of 2,4-dihydropyrrolo[3,4- ]indoles 43 (equation 2) [81]. A Diels-Alder reaction of 43 (R=Me, R =Bn) with DMAD gave the cycloadduct in 70% yield, which on exposure to tosic acid yielded dimethyl 4-benzylamino-l-methyl-5-(phenylsulfonyl)carbazole-2,3-dicarboxylate (68% yield). Snyder and coworkers described a novel pyri-dazine reductive ring contraction, as explored by Boger... 

Another pioneer in the Diels-Alder reactions of vinylpyrroles was Noland, who also developed the reactions of vinylindoles to yield carbazoles. Some examples of the former are shown in Scheme 2 (equations 1 and 2) [4-7], Jones and his colleagues were equally active in this cycloaddition chemistry of vinylpyrroles (equations 3 and 4) [8-12], These workers measured the rates of the reaction between 1-methyl-2-vinylpyrrole and seven dienophiles, with maleic anhydride being 4800 to 50,000 times more reactive than the other dienophiles (DMAD, maleonitrile, fumaronitrile, dimethyl maleate, methyl acrylate, and acrylonitrile) [8], In a clever tactic to thwart the formation of dihydroindoles, Jones used an excess of methyl propio-late to convert the initial adduct to a second Diels-Alder cycloadduct that subsequently loses ethene by a retro-Diels-Alder reaction to afford the dimethyl 1-methyl (phenyl)-4,7-dicarboxylates (equation 4). The reactions are concerted and were consistent with FMO calculations (HOMO[vinylpyrrole]-LUMO[alkene]). The yields are 54% to 81%, but attempts to dehydrogenate the tetrahydroindole products to indoles were unsuccessful. 2-Vinylpyrrole itself undergoes Michael additions and polymerization with these dienophiles. Domingo, Jones, and coworkers subsequently... 

Urea added portionwise during 1 hr. to a refluxing mixture of 9-methylcarbazole, acetic acid, and anhydrous AICI3, refluxing continued 2-2.5 hrs. 9-methyl-carbazole-3,6-dicarboxylic acid diamide. Y 87-88%. F. e. s. V. V. Gordshtein, V. P. Lopatinskii, and E. E. Sirotkina, Izv. Tomsk. Politekh. Inst. 185, 122 (1970) C. A. 75, 63532. 

The polyester (27b) with carbazole groups in the main chain was prepared by polycondensation of N-octylcarbazole-3,6-dicarboxylic acid with ethylene glycol [221]. The polymer is soluble in tetrahydrofuran and 1,1,2,2-tetrachloroethane. Its molecular weight (Af ) is 8300. The polymer (27b) is thermaly stable up to 420°C, and its chemical doping by iodine yields a semiconductor material with a conductivity of 10 S cm . 

A polyester of similar structure but with a much higher concentration of chromophores (carbazole is also present as a pendent) has been prepared by Rovkina et al. [222] (28). It was prepared by polycondensation of (9-carbazolylmethyl)oxirane or (9-carbazolyl)-2,3-dihydroxypropane with 9-alkylcar-bazole-3,6-dicarboxylic acids. The relative molecular mass of the polyesters is rather low (990-3370), so they are soluble in polar organic solvents and form elastic films with good adhesion to different substrates. When doped with TNF, the polyesters (28) exhibit photoconductivity. 

Rovkina et al. [222,280] reported on the synthesis of oligoesters having pendant carbazole groups. They were prepared by polycondensation of EPK (32a) or 3-(9-carbazolyl)propane-diol-l,2 (34a) with dicarboxylic acids (adipic, sebacic or phthalic). The carbazole-containing oligoesters had relative molecular masses from 640 to 2640 and exhibited photoconductivity and good film-forming properties. 

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