Imines manganese dioxide

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). 

Electrophilic aromatic substitution of the arylamine 780a using the iron-complex salt 602 afforded the iron-complex 785. Oxidative cyclization of complex 785 in toluene at room temperature with very active manganese dioxide afforded carbazomycin A (260) in 25% yield, along with the tricarbonyliron-complexed 4b,8a-dihydro-3H-carbazol-3-one (786) (17% yield). The quinone imine 786 was also converted to carbazomycin A (260) by a sequence of demetalation and O-methylation (Scheme 5.86). The synthesis via the iron-mediated arylamine cyclization provides carbazomycin A (260) in two steps and 21% overall yield based on 602 (607-609) (Scheme 5.86). 

The total synthesis of carbazomycin D (263) was completed using the quinone imine cyclization route as described for the total synthesis of carbazomycin A (261) (see Scheme 5.86). Electrophilic substitution of the arylamine 780a by reaction with the complex salt 779 provided the iron complex 800. Using different grades of manganese dioxide, the oxidative cyclization of complex 800 was achieved in a two-step sequence to afford the tricarbonyliron complexes 801 (38%) and 802 (4%). By a subsequent proton-catalyzed isomerization, the 8-methoxy isomer 802 could be quantitatively transformed to the 6-methoxy isomer 801 due to the regio-directing effect of the 2-methoxy substituent of the intermediate cyclohexadienyl cation. Demetalation of complex 801 with trimethylamine N-oxide, followed by O-methylation of the intermediate 3-hydroxycarbazole derivative, provided carbazomycin D (263) (five steps and 23% overall yield based on 779) (611) (Scheme 5.91). 

Arylazoarylimines (527), with a methyl or ethyl group ortho to the imine function (prepared by oxidation with manganese dioxide of arylaminohydrazones from anilines (525) and chlorohydrazones... 

Another aspect of the mode of action of ellipticine and its derivatives that has been intensely scrutinized in recent years is the chemistry of ellipticine quinone imines 6 and 256. The oxidation product of 9-hydroxyellipticine (3), formed by horseradish peroxidase-hydrogen peroxide or chemical (e.g., manganese dioxide) oxidation of 3, undergoes a rich array of chemical reactions. Meunier et al. 

Secondary amines having hydrogens on the a carbon are dehydrogenated to imines by mercuric acetate or manganese dioxide [825, 1091]. Piperidines give A -piperideines [1091] (equations 511 and 512). 

An efficient conversion of a hydroxy-imine into a fused oxazole ring under relatively mild conditions is effected by either silver oxide or thionyl chloride. Ekirium manganate is claimed to be more efficient than manganese dioxide in this cyclization. 

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 arylazoarylimines (48), carrying an aromatic methyl or ethyl group on the ortho position to the imine function and prepared by the reaction of anilines (46) with chlorohydrazones (47) in the presence of triethylamine followed by oxidation with manganese dioxide of the resulting arylamino-hydrazones, underwent thermal intramolecular cyclization in refluxing xylene in the presence of a catalytic amount of dabco to give the l/f-4,5-dihydro-l,3,4-benzotriazepines (49) in 50-87% yields (Scheme 7) <86JHC1795>. 

When the aniline moiety of iron complex 57 has a p-anisidine structure, the iron complex can be oxidized selectively to quinone imine 59 using commercial manganese oxide. Thus, oxidative cyclization of the quinone imines 59 using highly active manganese dioxide and demetallation provides 3-hydroxycarbazoles 60 directly (Scheme 23.23) [30]. 

Quinone imine-substituted ( n -cyclohexa-l,3-diene)iron complexes are obtained by oxidation of the corresponding p-anisidine precursors with manganese dioxide (Scheme 4—133). Treatment of the former species with very active manganese dioxide triggers an oxidative cyclization to afford iron-coordinated 4b,8a-dihydrocarbazol-3-Demetalation with trimethylamine N-oxide leads via concomitant... 

Very active manganese dioxide (320 mg) is added to a solution of the quinone imine complex (63 mg, 0.152 mmol) in dichloromethane (3 mL) and the heterogeneous reaetion mixture is stirred for 2 h at room temperature. By addition of very active Mn02 (80 mg) and stirring for additional 2 h at room temperature, the reaction is completed. The mixture is filtered through a short path of silica gel/Celite that is subsequently washed with ethyl acetate. The solvent is removed in vacuo and the residue is subjected to flash chromatography (hexane/ethyl acetate 5 1) on silica gel to afford the carbazolone iron complex as yellow crystals mp > 165 °C (decomp.) 49 mg (78%). ... 

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