Regioselective Synthesis of Substituted Carbazoles, Bicarbazoles, and Clausine C

Abstract

Substituted carbazoles are efficiently constructed from 3-triflato-2-pyrones and alkynyl anilines. Multiple substituents are tolerated on the carbazole, and complete control of regiochemistry is observed. Complicated and sterically congested substitution patterns are produced. This strategy is also used to prepare substituted bicarbazoles and related biaryls. Finally, the method was showcased in a synthesis of the carbazole natural product clausine C.

tert-Butyl(2-oxo-2H-pyran-5-yl)carbamate as the First Chameleon Diene Bearing an Electron-Donating Substituent

“…Ring substituents play a critical role in the cycloadditions of 2( H )pyran-2-ones. Generally speaking, the unsubstituted ring 2( H )pyran-2-one, 18 ( Figure 2 ), undergoes cycloadditions only under harsh conditions and with alkynes to afford benzenes following the tandem loss of CO 2 [ 1 , 2 , 3 , 4 , 5 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. Examples of cycloadditions of 2( H )pyran-2-one, 18, with alkenes to afford bridged bicyclic lactones do exist, but are rare [ 65 , 66 , 67 , 68 , 69 , 70 ].…”

“…In particular, cycloadditions of 2( H )pyran-2-one dienes to alkene dienophiles affords bridged bicyclic lactones, e.g., 2 which can then be transformed in few steps to highly substituted, six-membered rings, e.g., 3 ( Scheme 1 ) [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. Under more forcing conditions, typically at higher temperatures, cycloadditions to alkyne dienophiles and subsequent aromatization via loss of bridging CO 2 leads to substituted benzenes, e.g., 4 [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ].…”

Preparation of Some New Pyrazine and Triazine Derivatives and Study of their Antimicrobial and Anticancer activities

“…The reaction mixture was then allowed to cool to room temperature, and the solid material was filtered, dried, and recrystallized from the acetone. The physical characteristics and FT-IR spectral data of compounds (3)(4)(5) are shown in Table 2. (8) [27] Compounds (3-5) (0.001 mol) in a solution of sodium hydroxide (20 mL, 4.0 N) were refluxed for 5-6 hours.…”

“…The diazine derivatives have gained a great deal of attention in the present day as a result of their many advantageous traits. For instance, the ease with which structural alterations can be made [4], the excellent electrical and optical properties [5], and the beneficial biological activities [6]. The pyridazine, which has been known as the "wonder nucleus", as well as its derivatives, were reported because of their biological and chemical actions to have a broad variety of biological activities [7], which include potent and anti-hypertensive cardiotonic agents [8].…”

Lewis Acid-Catalyzed 2,3-Dihydrofuran Acetal Ring-Opening Benzannulations toward Functionalized 1-Hydroxycarbazoles

“…The synthesis of carbazoles generally follows two distinct approaches ( Figure 2 ): (a) an annulation reaction to generate the central pyrrole ring or (b) a benzannulation reaction in which a benzene ring is appended on the five-member ring of an indole [ 15 , 16 , 17 , 18 , 19 ]. While several syntheses have been reported [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ], the abundant presence of the carbazole core in bioactive molecules and photoelectronic materials makes them attractive targets for the development of new synthetic methodologies, often targeting new substitution patterns, modularity and mild reaction conditions.…”