title: Multifold C-C Coupling and Unorthodox Cyclization Catalysis for Selective Synthesis of Indolotriarylmethanes, Indolocarbazoles, and Their Analogues: A Control Experiment Study.
abstract: The selective construction of medicinally and synthetically important indole-based unsymmetrical triarylmethanes using indoles and aldehydes is challenging because the significant nucleophilicity of indole leads to C-C coupling with an azafulvene intermediate to build up the alternative bis(indolyl)methane products, which may be useful synthons. A new, straightforward, ligand-free CuIIcatalytic strategy for easy syntheses of unsymmetrical indolotriarylmethanes and new bisindolylbenzoyl analogues is established through the dual C-C coupling of an assembly of three reaction partners comprising aldehydes, indoles, and arylboronic acids. More importantly, this approach is exploited for multifold C-C coupling cyclization reactions with C-C cleavage using symmetrical bisindolylbenzoylmethanes in the presence of an organic base and aerial molecular oxygen as a stoichiometric oxidant. In contrast to the formation of a simple cyclocondensation product indolocarbazole, it undergoes unprecedented selective pseudo-four-component tandem oxidative cyclization with fragmentation from a 1,3-dicarbonyl compound to produce valuable fused 5,7-dihydroindolo[2,3-b]carbazoles through the functionalization of two indole C(sp2)-H and one C(sp3)-H bond of the active methylene residue. For a better understanding of the new reactions, we have studied various competition experiments and ESI-MS and 3D Mid-IR-ATR spectral analyses of the ongoing reactions. The predicted DFT transition state model is also in agreement with the experimental results.
authors.affiliation: Department of Chemistry, University of Calcutta , 92 A. P. C. Road, Kolkata 700009, India.
authors.forename: Tuluma
authors.initials: T
authors.lastname: Das
authors.affiliation: Department of Chemistry, University of Calcutta , 92 A. P. C. Road, Kolkata 700009, India.
authors.forename: Sudipto
authors.initials: S
authors.lastname: Debnath
authors.affiliation: Department of Chemistry, University of Calcutta , 92 A. P. C. Road, Kolkata 700009, India.
authors.forename: Rituparna
authors.initials: R
authors.lastname: Maiti
authors.affiliation: Department of Chemistry, University of Calcutta , 92 A. P. C. Road, Kolkata 700009, India.
authors.forename: Dilip K
authors.identifier: 0000-0001-8743-2620
authors.initials: DK
authors.lastname: Maiti