Dihydrocarbazoles synthesis

The procedure is also applicable to acetoxy-substituted arylamines, thus broadening the scope of the carbazole synthesis (Scheme 22). Reaction of the complex salt 6a with the 5-acetoxyarylamines 56 affords the tricarbonyliron-complexed 4a,9a-dihydrocarbazoles 57, which on demetalation and subsequent catalytic dehydrogenation [100] give the 4-acetoxycarbazoles 58. Removal of... 

Diels-Alder reaction of vinylindoles with dienophiles has been established as a versatile and flexible methodology for the synthesis of carbazole alkaloids. Among the two different vinylindoles, 3-vinylindoles were the first to be explored for the Diels-Alder cycloaddition methodology with a range of dienophiles to give polyfunctionalized carbazole derivatives. This reaction is catalyzed by tiifluoroacetic acid, and the yield in the absence of the acidic catalyst is very low. The reaction of substituted 3-vinylindoles 550 and 553 with ethylenic dienophiles 551 and acetylenic dienophiles 535 leads, via a tetrahydrocarbazole and a dihydrocarbazole, to the corresponding carbazoles (552 and 554), respectively (530,531) (Scheme 5.18). 

Using a modification of Sakamoto s indole benzannulation protocol (see Scheme 5.59), Beccalli et al. reported the synthesis of the 3-methoxycarbazole alkaloids hyellazole (245) and 6-chlorohyellazole (246) (540) (Scheme 5.61). Unlike Sakamoto s methodology, this method requires a good leaving group at the 2-position of the indole moiety of the 3-(l,3-butadienyl)indoles 692 to facilitate the aromatization of the intermediate dihydrocarbazole by eliminating the dehydrogenation step. 

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]. 

Fischer indole synthesis, of 1,2-benzo-3,4-dihydrocarbazole, 30, 91 of 1,2,3,4-tetrahydrocarbazole, 30, 90 Flavilium chloride, 32, 75 Flavone, 32, 72 Formaldehyde, 30, 51 or-Formylethyl methyl ketone, 32, 34 Formyl isobutyl ketone, 32, 34 Friedel-Crafts reaction, 30, 1 31, 88 32, 10... 

Demetalation of 4 with trimethylamine N-oxide yields car-bazole 5. Methylation gives carbazomycin A (1) [12]. In addition to carbazoles, Kndiker and his students applied this iron-mediated chemistry to the preparation of dihydroindoles [13, 14], (anhydrolycotine), tetrahydroindoles [15], dihydrocarbazoles [16], perhydroacenaphihenes [17], and azaspiroannelated ring systans [18-21], Several shorter accounts of Kndlker s carbazole syntheses [22-25] and the overall utility of tricarbonyl(Tl -diene)iron complexes in organic synthesis are available [26-32],... 

Silylated diynes are used in the synthesis of methylene cyclopentanes, notably acyl derivatives of Oppoizer s camphor sultam, enediyne antibiotics, and CpCo omplexed dihydrocarbazoles, and ( )-Lysergene and (+)-LSD from a substituted indole and Me3SiC=CR through a [2+2+2]cycloaddition. Monosilylated hexatriyne and octatetrayne are used in the synthesis of the caryoynencin polyyne antibiotics, while triflate substituted disilyl polyynes result from the corresponding allyl derivative with The hydropyrolysis of bis-... 

The first example of Rh-catalyzed C-H coupling of 2-phenylpyridines with 7-azabenzonorbornadienes to provide czs-fused dihydrocarbazoles 39 was reported by Li and coworkers (Eq. (5.38)) [23]. The C-N bond forms via a double C-H activation, in which a seven-membered rhodacyclic complex is a key intermediate as a result of stereoselective insertion of the olefin into the Rh-C(aryl) bond. This strategy has also been employed for the synthesis of dihydrocarbazoles by using various directing groups. 

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