Noble-Metal-Free C-H Allylation of Tetrahydroisoquinolines Using a Cobalt-Organophotoredox Dual Catalyst System.

Metallaphotoredox-catalyzed allylation represents an emerging synthetic methodology that enables allylic substitution using nucleophilic radical species. The C-H allylation of N-aryl tetrahydroisoquinolines is an innovative example in this area and allows access to synthetically useful precursors for the further derivatization of tetrahydroisoquinolines. However, previous methods have required the use of noble metals, which has hampered their application due to concerns over their sustainability. Here we report the C-H allylation of N-aryl tetrahydroisoquinolines using a cobalt/organophotoredox dual catalyst system. Based on precedent, control experiments and controlled irradiation experiments, a mechanism for the cobalt/photoredox-catalyzed allylation that involves a π-allyl cobalt complex is proposed.

Cobalt-Catalyzed Allylic Alkylation Enabled by Organophotoredox Catalysis.

Co-catalyzed allylic substitution reactions have received little attention, arguably because of the lack of any known advantage of Co catalysis over either Rh or Ir catalysis. Described here is a general and regioselective Co-catalyzed allylic alkylation using an in situ catalyst activation by organophotoredox catalysis. This noble-metal-free catalytic system exhibits unprecedentedly high reactivities and regioselectivities for the allylation with an allyl sulfone, for the first time, representing the unique synthetic utility of the Co-catalyzed method compared to the related Rh- and Ir-catalyzed reactions.

Palladium-Catalyzed External-CO-Free Carbonylation of Aryl Bromides Using 2,4,6-Trichlorophenyl Formate.

A practical Pd-catalyzed carbonylation of (hetero)aryl bromides using a crystalline carbon monoxide (CO) surrogate, 2,4,6-trichlorophenyl formate (TCPF), was developed. This reaction proceeds without the slow addition technique that was previously required and with a low catalyst loading (1 mol%). The utility of this Pd-catalyzed external-CO-free carbonylation using TCPF was demonstrated in the synthesis of a histone deacetylase inhibitor.

Regioselective Deaminative Allylation of Aliphatic Amines via Dual Cobalt and Organophotoredox Catalysis.

Despite the rapid progress in C-C bond-forming reactions using Katritzky salts, their deaminative allylation remains a challenge. Inspired by the metallaphotoredox-catalyzed allylic substitution regime, here, we report the deaminative allylation of Katritzky salts via cobalt/organophotoredox dual catalysis. This cross-electrophile coupling enables regioselective allylation using a variety of allylic esters, overcoming the substrate limitations of reported protocols. Mechanistic studies indicate the involvement of a π-allyl cobalt complex as a radicalophile that mediates C-C bond formation.