3‑Alkynylindoles as Building Blocks for the Synthesis of Electronically Tunable Indole-Based Push–Pull Chromophores

• Published in: Journal of organic chemistry Vol. 87; no. 6; pp. 4385 - 4399
• Main Authors: Erden, Kübra, Dengiz, Cagatay
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 18.03.2022; Amer Chemical Soc
• Subjects: alkynes; Alkynes - chemistry; Chemistry; Chemistry, Organic; Density Functional Theory; Indoles; Models, Molecular; organic chemistry; Physical Sciences; regioselectivity; Science & Technology; MILD CONDITIONS; TCNQ; CLICK CHEMISTRY; DIELS-ALDER REACTION; REGIOSELECTIVE SYNTHESIS; 2+2 CYCLOADDITION-RETROELECTROCYCLIZATION; DONOR-ACCEPTOR MOLECULES; OPTOELECTRONIC PROPERTIES; CHARGE-TRANSFER CHROMOPHORES; HIGHLY EFFICIENT
• ISSN: 0022-3263; 1520-6904; 1520-6904
• DOI: 10.1021/acs.joc.2c00067

In this study, two different classes of push–pull chromophores were synthesized in modest to excellent yields by formal [2+2] cycloaddition-retroelectrocyclization (CA-RE) reactions. N-Methyl indole was introduced as a new donor group to activate alkynes in the CA-RE transformations. Depending on the side groups’ size and donor/acceptor characteristics, N-methyl indole-containing compounds exhibited λmax values ranging between 378 and 658 nm. The optoelectronic properties of the reported D–A-type structures were studied by UV/vis spectroscopy and computational studies. The complete regioselectivity observed in the products was elaborated by one-dimensional (1D) and two-dimensional (2D) NMR studies, and the electron donor strength order of N-alkyl indole and triazene donor groups was also established. The intramolecular charge-transfer characteristics of the target push–pull chromophores were investigated by frontier orbital depictions, electrostatic potential maps, and time-dependent density functional theory calculations. Overall, the computational and experimental results match each other. Integrating a new donor group, N-alkyl indole, into the substrates used in formal [2+2] cycloaddition-retroelectrocyclizations has significant potential to overcome the limited donor-substituted substrate scope problem of CA-RE reactions.