Agneswaran R, Mohanakrishnan AK. Synthesis of α-, β-, and γ-Carbolines via Intramolecular Cyclization of Azidomethyl(indolyl)acrylates Involving PIFA-BF
3·OEt
2/DBU-Mediated Cyclization as well as Thermolysis Approaches.
J Org Chem 2024;
89:9867-9887. [PMID:
38955671 DOI:
10.1021/acs.joc.4c00571]
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Abstract
In this study, we present our findings on the synthesis of α-, β-, γ-carbolines via PIFA/BF3·OEt2-mediated intramolecular cyclization of isomeric azidomethyl(indolyl)acrylates. Alternately, 1,5,7-triazabicyclo[4.4.0]dec-5-ene/1,8-diazabicyclo(5.4.0)undec-7-ene (TBD/DBU)-mediated Michael addition followed by intramolecular cyclization of isomeric 2/3-(azidomethyl)indol-3/2-yl)acrylates also furnished the respective β- and γ-carboline derivatives. Unexpectedly, the thermolysis of 2-(azidomethyl)-3-(indol-3-yl)acrylates led to the formation of ethyl 5-(2-(phenylsulfonamido)aryl)nicotinates along with γ-carbolines, via nitrene insertion followed by rearrangement and cyclization. The isomeric 2-(azidomethyl)-3-(indol-2-yl)acrylate upon thermolysis led to the expected δ-carboline. Thermal intramolecular nitrene insertion reaction could also be extended for accessing pyrido benzothiophene, pyrido thiophene, and quinoline.
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