A straight access to functionalized carbazoles by tandem reaction between indole and nitrobutadienes

Sequential Annulations to Interesting Novel Pyrrolo[3,2-c]carbazoles

“…As already ascertained in other processes, we found, in recent years [27,28], that the more reactive electrophilic site within 4 -type butadienes is the nitrovinylic moiety, presumably leading, as a first intermediate, to the Michael adduct 12 (Scheme 6), analogous to that ( 13 ) hypothesized for the reaction with indole [16]. Of course, due to the different site-selectivity of the considered heterocycles, the new bond involves C2 of pyrrole, while in the case of indole involves C3.…”

“…As a matter of fact, experimental results in previously studied systems, as well as Baldwin’s rules [31], encouraged us to consider the intermediate 15 as the most likely one, although it is only through 14 that 9 can originate. Thus, the observed distribution could be the result of a competition between these two alternative cyclization ways, rather than the consequence of different evolutions of 14 , with 15 playing a significant role anyway: In this regard, it is worth mentioning what we observed in the reactions with indole, where a trisubstituted derivative analogous to 9 was generally the main product (Scheme 8, results from [16]).…”

“…In this regard, it should be recalled that in our experience, nitroindoles and nitrocarbazoles are not easily reduced when the nitro groups are positioned on C5 and C3, respectively, as expected when considering the electron-donating effect of the ring nitrogens. Particularly representative of this noteworthy different reducibility was the result [16] obtained from 1,4-diaryl-2,3-dinitrocarbazole (Ar = p -Tol, Scheme 4), for which the reduction of the two nitro groups proceeded with such different rates as to reveal a high regioselectivity.…”

“…In this context it should be placed our recent work on the benzannulation of indole [16,17], employing versatile nitrobutadienic building blocks ( 3 , 4 in Scheme 1, parts a and c , respectively) obtained from the initial ring opening of suitably substituted nitrothiophenes ( 1 , 2 ) [18,19,20]. Thus, mixtures of 2- and 3-nitro-, or 2,3-dinitro-1,4-diarylcarbazoles were obtained from indole by action of 2,3-dinitrobutadienes 3 , while when employing mononitrobutadienes 4 , 4-aryl-3-nitrocarbazoles were generated as the main products.…”

Synthesis and Biological Evaluation of S-Substituted Perhalo-2-nitrobuta-1,3-dienes as Novel Xanthine Oxidase, Tyrosinase, Elastase, and Neuraminidase Inhibitors

“…These synthesized compounds are important in pharmacology. S-, N-, N,S-substituted polyhalonitrobutadiene compounds obtained by the reactions of polyhalonitrobutadiene compounds with various nucleophilic reagents such as thiols, dithiols, and amines are given in the literature [1][2][3][4][5][6][7][8][9]. There are studies on antifungal, antibacterial, anticancer, and anti-HIV properties of these compounds [10][11][12][13][14][15][16].…”