Electrochemical Synthesis of Hetero[7]helicenes Containing Pyrrole and Furan Rings via an Oxidative Heterocoupling and Dehydrative Cyclization Sequence

Abstract

The electrochemical synthesis of hetero [7]helicenes including pyrrole and furan rings has been established. A single electrochemical operation led to an oxidative heterocoupling and dehydrative cyclization sequence to afford oxaza [7]helicenes in 50-86% yields with 45-77% Faradic efficiencies. Their derivatization and chiroptical properties were also investigated.

Substitution Effects on the Photophysical and Photoredox Properties of Tetraaza[7]helicenes

“…Placing a CF 3 -group or a C 6 F 5 -group in the same position (model substrates 7 h, 7 i) results in a strong stabilization compared to the non-fluorinated substituents (À 0.71 eV CH 3 !CF 3 , À 0.47 eV Ph!C 6 F 5 ). The LUMO energy of the methylated 7 b is raised to a similar extent (+ 0.11 eV) as the HOMO, resulting in comparable absorption and emission bands of 7 a and 7 b but an easier oxidation of 7 b. Fluorination on the inner ring positions (1,16) does not influence the HOMO level but fluorination in the 3,14-position stabilizes it by À 0.23 eV. LUMOs of the fluorinated derivatives 7 d and 7 e are shifted similarly to the HOMOs, with the 1,16-F-substitution having a lesser stabilizing effect compared to the 3,14-substitution (À 0.06 eV and À 0.27 eV).…”

“…The research interest in helicenes has grown in recent years, driven by the increasing number of synthetic approaches [1][2][3][4][5][6][7][8] and the desire to exploit the unique properties of this class of compounds, which originate from their helical structure in combination with the extended aromatic system. Helicenes find a wide variety of applications, such as synthetic use in the preparation of chiral catalysts, often in the form of ligands, or more exotic applications including the construction of molecular machines.…”

Helicity-modulated remote C-H functionalization

“…1B). Electrochemistry (28)(29)(30)(31)(32)(33)(34)(35)(36) was used to activate the helical substrates (37)(38)(39), and alkoxylation was simultaneously conducted under mild conditions. It was found that the first-position aryl hydrogen H A1 of the helical skeleton acted as a directing group to promote the remote alkoxylation by generating a unique "back-biting" environment.…”

Bismuth(III)-Catalyzed Oxidative Cross-Coupling of 3-Hydroxycarbazoles with Arenols under an Oxygen Atmosphere

“…Sasai and Takizawa et al reported an electronic method to avoid the use of transition metals lately. 37,38 Organobismuth(V) compounds can be used in stoichiometric arylation reactions (Scheme 2B). Barton et al reported the arylation of arenols using stoichiometric triaryl Bi(V) 9,10 to afford C 1 -symmetric hydroxybiaryls.…”

“…This problem can be overcome using heterogeneous catalysts; , however, certain limitations, such as metal-catalyst leaching, still remain. Sasai and Takizawa et al reported an electronic method to avoid the use of transition metals lately. , Organobismuth­(V) compounds can be used in stoichiometric arylation reactions (Scheme B). Barton et al reported the arylation of arenols using stoichiometric triaryl Bi­(V) , to afford C 1 -symmetric hydroxybiaryls. , In addition, Ball et al reported the regioselective arylation of arenols using stoichiometric Bi­(V) species generated from the in situ reaction of Bi­(III) and m -chloroperoxybenzoic acid ( m CPBA). , However, to the best of our knowledge, there have been no reports on Bi-catalyzed oxidative couplings between two arenols.…”