Dihydrocarbazol-4 -ones

Electrophilic aromatic substitution of 708 with the iron-coordinated cation 602 afforded the iron-complex 714 quantitatively. The iron-mediated quinone imine cyclization of complex 714, by sequential application of two, differently activated, manganese dioxide reagents, provided the iron-coordinated 4b,8a-dihydrocarbazole-3-one 716. Demetalation of the iron complex 716 with concomitant... 

Electrophilic substitution at the arylamine 709 using the complex salt 602, provided the iron complex 725 quantitatively. Sequential, highly chemoselective oxidation of the iron complex 725 with two, differently activated, manganese dioxide reagents provided the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727) via the non-cyclized quinone imine 726. Demetalation of the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727), followed by selective O-methylation, provided hyellazole (245) (599,600) (Scheme 5.70). 

The construction of the carbazole framework was achieved by slightly modifying the reaction conditions previously reported for the racemic synthesis (614). Reaction of the iron complex salt 602 with the fully functionalized arylamine 814 in air provided the tricarbonyliron-coordinated 4b,8a-dihydrocarbazole complex 819 via sequential C-C and C-N bond formation. This one-pot annulation is the result of an electrophilic aromatic substitution and a subsequent iron-mediated oxidative cyclization by air as the oxidizing agent. The aromatization with concomitant demetalation of complex 819 using NBS under basic reaction conditions, led to the carbazole. Using the same reagent under acidic reaction conditions the carbazole was... 

Chemoselective oxidation of 4-methoxyanilines to quinonimines can be achieved in the presence of tricarbonyl(ri4-cyclohexadiene)iron complexes. This transformation has been used for the synthesis of carbazoles via intermediate tricarbonyliron-coordinated 4b,8a-dihydrocarbazol-3-one complexes (Scheme 1.24) [57]. 

A further route, via initial oxidation of the arylamine to a quinonimine followed by oxidative cyclization to an iron-coordinated 4b,8a-dihydrocarbazol-3-one and demetallation to a 3-hydroxycarbazole, has been described above (Scheme 1.24). 

In the presence of external protic acid, A-alkyl-iV-(4-methoxyphenyl)anilines (54a-59a) are converted to A-alkyl-l,2,4,9-tetrahydrocarbazol-3-ones (54b-59b) (equations 14—16)162. A conceivable mechanism is demonstrated for 54a in Scheme 8, where the dihydrocarbazole intermediate undergoes a successive formal [1,5] and [1,3] hydrogen shift and then acid assisted hydrolysis before the formation of final products. 

Similarly, direct photolysis of enaminones 232 resulted in the formation of trans-2ii in very high yields, Scheme 62 (85TL2323 89CJC213). Photolysis of bromo-substituted aryl enaminones also afforded high yields of dihydrocarbazol-4(5//)-ones [87JCS(CC)766],... 

Alternatively, a mild and efficient one-pot electrophilic aromatic substitution/ oxidative cyclization without isolation of the intermediate complexes 36 has been achieved using air as oxidizing agent (mode B in Scheme 12). Thus, reaction via mode B leads to tricarbonyl(ri" -4a,9a-dihydrocarbazole)iron complexes 37, which on demetalation with trimethylamine A(-oxide and subsequent catalytic dehydrogenation provide the carbazoles 40. The naturally occurring carbazole... 

A third pathway leads via the quinone imine intermediates 38 to 3-hydro-xycarbazoles 41 (mode C in Scheme 12) [97, 98, 108, 109]. Oxidation of the complexes 36 with manganese dioxide afforded the quinone imines 38, which on treatment with very active manganese dioxide undergo oxidative cyclization to the tricarbonyl(ri" -4b,8a-dihydrocarbazol-3-one)iron complexes 39. Demetalation of 39 with trimethylamine iV-oxide and subsequent aromatization lead to the 3-hydro-xycarbazoles 41. The isomerization providing the aromatic carbazole system is a... 

The indole 2-3 double bond can participate in a cobalt-mediated combination with two alkyne units. In particular, when one of the alkynes is tethered to the indole nitrogen atom by an acyl group, cyclization occurs to give an unusual dihydrocarbazole such as compound (286), which can be demetallated either to the dihydrocarbazole (287) or to the carbazole (288) (Scheme 84) <86JA2091>. 

Pyrano[3,4-6]indol-3-one (329) enters the Diels-Alder reaction with methoxy-butenone as an electron-rich olefin [92JCS(P1)415]. After decarboxylation of the primary adduct330,2-acetyl-3-methoxy-1,9-dimethy 1-2,3-dihydrocarbazole (331) eliminates methanol to form 2-acetyl-1,9-dimethylcarbazole (332) [92JCS (Pl)415]. 

The requisite tricarbonyl(ii -cyclohexadienylium)iron cation 2 is prepared from 1,3-cyclohexadiene and FefCOlj followed by treatment with triphenylmethyl carbocation tetrafluoroborate as shown. Subsequent oxidative cyclization of iron complex 3 with commercial manganese dioxide affords the iron-complexed dihydrocarbazol-3-one 4. 

Many of the multianalyte studies developed methods for the simultaneous determination of compoimds from the two major classes of neurotransmitters amino acids and bioamines. In one example, DA, serotonin, the serotonin metabolite 5-hydroxyindole acetic acid, glutamate, and GABA were quantified concurrently from tissue preparations using fluorescence detection following derivatization with a novel synthetic compoimd, l,2-benzo-3,4-dihydrocarbazole-9-ethyl... 

The electrophilic aromatic substitution of amine (44) by iron com-plexed cation (43) at room temperature provided (48) after three days while the complex (45) was obtained after two hours. Oxidative cyclis-ation of (45) as such was not facile. Acetylation to (46) followed by oxidation with Mn02 gave O-acylcarbazomycin B (47) which on deacetylation furnished carbazomycin B (5). However selective oxidation of (48) provided dihydrocarbazole-3-one (49). Demetallation with tri-... 

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