Synthesis of Carbazoles via an Intramolecular Cyclization of 2-(6-Substituted 3(Z)-hexen-1,5-diynyl)anilines and Their Related Molecules

Abstract

Various 2-(6-substituted 3(Z)-hexen-1,5-diynyl)anilines 1a-g were treated with potassium tert-butoxide or potassium 3-ethylpentanoxide in NMP at 60 degrees C for 2 h to give the corresponding 5-substituted carbazoles 2a-g in 36-65% yields together with indoles 9a-g in 21-40% yields, respectively. Exposing the trifluoroacetamide analogues 10h-k under the same reaction conditions gave the carbazoles 2b-e in 37-57% yields and indoles 9b-e in 15-27% yields. Subsequent cyclizations of acetamide analogues 10a-g gave carbazoles 2a-g in 53-86% yields.

Development and applications of highly selective palladium-catalyzed monocoupling reactions of (cyclo)alkenes and 1,3-alkadienes bearing two or three electrophilic sites and bis(enol triflates) with terminal alkynes

“…136 In 2004, Wu and coworkers synthesized 4-butyl-9Hcarbazole (252a) in 58% yield by treatment of 2-(6-butyl-3(Z)-hexen-1,5-diynyl)aniline (251a) with t-BuOK in NMP at 60 °C for 2 h (Scheme 85). 137 The synthesis of compound 251a from 1 was accomplished according to a reaction sequence that involved the efficient conversion of 1 into 4 and CuI to give 251a in 39% yield. 137 Noteworthy, the intramolecular anionic cyclization of 251a gave 252a along with the indole derivative 253a in 21% yield.…”

“…137 The synthesis of compound 251a from 1 was accomplished according to a reaction sequence that involved the efficient conversion of 1 into 4 and CuI to give 251a in 39% yield. 137 Noteworthy, the intramolecular anionic cyclization of 251a gave 252a along with the indole derivative 253a in 21% yield. In 2005, several 1-aryl-1H-benzotriazoles were prepared in high yields from (Z)-3-en-1,5-diynes 254, which were synthesized from (Z)-1-chloro-4-trimethylsilyl-1-buten-3yne (2e) as outlined in Scheme 87.…”

“…An extensive use of (Z)-1-chloro-1-en-3-ynes was made by Wu and coworkers in the synthesis of unsymmetrically substituted acyclic (Z)-3-en-1,5-diynes (used) as precursors to heterocycles. 93,[136][137][138][139][140] As previously mentioned (Scheme 53), enediyne 52a was employed as a starting material in the synthesis of the 2-substituted benzofuran 143. 93 Specifically, treatment of 243a with 5 equiv of sodium methoxide in refluxing MeOH for 6 h gave phenanthridine 244a in 4% yield along with phenathridinone 245a in 7% yield.…”

10.1007/s11176-008-2012-z

“…A new procedure was proposed for the synthesis of carbazoles via intramolecular anionic cyclization of 2-[(3Z)-alk-3-ene-1,5-diyn-1-yl]anilines (120); the product yields ranged from 65 to 85% (Scheme 34) [71]. The best yields were obtained in the cyclization of N-acetyl derivatives 120 (Y = COMe).…”

Design, Synthesis, and In vitro Evaluation of Thieno[a]dibenzothiophene Derivatives

“…Recently, electrophilic cyclization reactions (ECR) have been used for the synthesis of biologically important heterocyclic/aromatic structures such as; indoles, benzofuranes, benzopyrenes, isoxazoles, pyridines, carbazoles, benzo[ b ]naphtho[2,1‐ d ]thiophene and pyrazoles . ECR displayed high regio‐selectivity, needed mild reaction conditions and mostly shorter reaction time for the formation of designed molecules.…”