Formal [4 + 2] benzannulation of 2-alkenyl indoles with aldehydes: a route to structurally diverse carbazoles and bis-carbazoles

Abstract

Construction of structurally diverse carbazoles and bis-carbazoles by protecting-group-free formal [4 + 2]-benzannulation of 2-alkenyl indoles and aldehydes is demonstrated.

Oxidative Rearrangement of 2‐(2‐Aminobenzyl)furans: Synthesis of Functionalized Indoles and Carbazoles

“…[15] The commonly used route is based on various processes of the benzene ring fusion to readily available indoles. [16] Having obtained the efficient method for the synthesis of 3-substituted indoles bearing α,β-unsaturated ketone moiety at the C(2) atom, we designed a new simple approach to functionalized carbazole derivatives. To implement this idea, a substituent at the C(3) atom of the indole ring should have a CH-acid moiety at the α-position that can be involved into aldol condensation with unsaturated ketone functionality at the indole C(2) atom.…”

Synthesis of polysubstituted arenes through organocatalytic benzannulation

“…Besides, the same group successfully expanded the [4 + 2] benzannulation reaction of 15 with aldehydes for the synthesis of other multifunctionalized aromatic compounds. 16 In 2018, Chang's group reported an inverse-electron-demand Diels-Alder reaction between 1,2-diazines 20 and ynamides 21. 17 Optimizing the reaction conditions showed that the reaction proceeded well under the catalysis of Tf 2 O in DCE at 100 C. The catalytic protocol could tolerate various functional groups, both electron-rich and electron-decient substituents on 1,2diazines are compatible in the [4 + 2] benzannulation, giving a series of 2-aminonaphthalenes or 2-aminoanthracenes 22 in moderate to excellent yields (56-95%).…”

Towards bioresource-based aggregation-induced emission luminogens from lignin β-O-4 motifs as renewable resources

“…Employing carbazole as a core moiety, introducing two electron acceptor groups (i.e., benzoyl) into a carbazole scaffold might provide an efficient way for the preparation of A-D-A-type AIEgens. Moreover, extensive synthetic strategies of the functionalized carbazoles focus on intermolecular cross-coupling reactions between C-H/C-X bonds (X = halo, N, O, C, etc) 56 , oxidative intramolecular C-H/C-H cross coupling of prefunctionalized diarylamines 57 , the construction of a benzene ring upon substituted indoles through transition metal catalysis 58 or Brønsted acid catalysis 59 – 61 . However, most approaches suffer from the need of excess oxidants, multi-step reactions and the formation of non-renewable substrates, which raises atom economy and environmental concerns.…”