Room-Temperature C–H Bond Functionalization by Merging Cobalt and Photoredox Catalysis

Abstract

A non-noble metal-free protocol has been developed for C−H bond functionalization at room temperature by merging cobalt-mediated catalysis with photocatalysis. The reaction requires only oxygen as sole oxidant and operated at room temperature under redox-neutral conditions. Visible-light activated photoredox catalyst functions as an electron transfer reagent with oxygen as a terminal oxidant in the cobalt-mediated C−H and N−H bond annulation. The developed methodology allows annulations with various coupling partners. The concept demonstrated herein is expected to enhance the scope of cobalt catalysis as applied to sustainable fine chemical synthesis.

Metallaphotoredox-Catalyzed C−H Activation: Regio-Selective Annulation of Allenes with Benzamide

“…On the other hand, intermolecular competition studies suggested that the electron-rich amide was slightly more favorable, which could be rationalized an electrophilic-type substitution C − H metalation. Based on the mechanistic experiments described above and relevant literature reports [81][82] [77,86]. Thus the Co(III) species could be regenerated, and a strong reductant, Na 2 Eosin Y radical anion (-1.06 V vs SCE) [86] was simultaneously generated.…”

Cp*Co(III)‐Catalyzed o‐Amidation of Benzaldehydes with Dioxazolones Using Transient Directing Group Strategy

“…To the best of our knowledge, orthoamidation of aldehydes under first row transition metal catalysis has not been realized yet. [18] Our continuous interest in exploring CÀ H bond functionalization using weakly chelating directing groups under base metal catalysis [19] prompted us to develop an efficient and sustainable procedure for the synthesis of 2-aminobenzaldehydes. Towards this goal, herein, we disclose the cobalt-catalyzed ortho-selective C(sp 2 )À H amidation of benzaldehydes with dioxazolones as an easily accessible amidating reagent [11b,20] using Cp*Co(III) as catalyst (Scheme 1).…”

C–H Functionalization of Aromatic Amides

“…In 2018, Sundararaju and co‐workers also reported a C–H functionalization reaction also using 8‐aminoquinoline as the directing group and Co(acac) 2 as the catalyst (Scheme ) . Compared with the former, the advantage of this reaction was that it did not need stoichiometric Mn(III) as a co‐catalyst.…”