Cyclization of an alkene-bearing cyclopentanone: The role of rhodium and Brønsted acid

Cobalt-Catalyzed Deacylative Ipso-C-C Bond Functionalization: An Approach toward Indole-Acyloins and Its Photophysical Studies

Selective functionalization of the indole-C3-C bond with aromatic/heteroaromatic 1,2-diketones has been uncovered for the first time. Cobalt catalyst was found to be an effective catalyst for this unusual transformation. This ipso-C-C bond functionalization occurred in the presence of easily available weakly coordinating groups such as ketone and ester. One of the salient features of this methodology is the in situ generation of water from hexafluoro-2-propanol which acts as a reactant for the removal of the pivaloyl/ester group in a deacylative manner. The plausible mechanism has been supported by DFT calculations. Moreover, photophysical studies show the potential utility of indole-C3-acyloin and indolo-fused carbazole, which could be used in photovoltaic and optoelectronic application.

Stereoselective Dynamic Cyclization of Allylic Azides: Synthesis of Tetralins, Chromanes, and Tetrahydroquinolines

This report describes the stereoselective synthesis of 3-azido-tetralins, -chromanes, and -tetrahydroquinolines via a tandem allylic azide rearrangement/Friedel-Crafts alkylation. Exposure of allylic azides with a pendant trichloroacetimidate to catalytic quantities of AgSbF6 proved optimal for this transformation. This cascade successfully differentiates the equilibrating azide isomers, providing products in excellent yield and selectivity (>25 examples, up to 94% yield and >25:1 dr). In many cases, the reactive isomer is only a trace fraction of the equilibrium mixture, keenly illustrating the dynamic nature of these systems. We demonstrate the utility of this process via a synthesis of hasubanan.

Pursuing the active species in an aluminium-based Lewis acid system for catalytic Diels-Alder cycloadditions

Several Al-based complexes supported by a bis(imino)aryl NCN pincer ligand have been prepared. Systematic structural and experimental evidence identified a cationic species, supported by a THF molecule, as the best Lewis acid precatalyst for a range of Diels-Alder cycloadditions. This highlighted the importance of fully isolating and characterizing the active species in any catalytic process especially when Lewis acids are used due to the presence of hidden Brønsted acids (HBAs). Finally, the control experiments conducted in order to eliminate HBA activity that involve a bulky pyridine base should be performed with caution as the corresponding protonated pyridinium salt could also serve as a proton source.