A Desaturative Approach for Aromatic Aldehyde Synthesis via Synergistic Enamine, Photoredox and Cobalt Triple Catalysis

Abstract

Aromatic aldehydes are fundamental intermediates that are widely utilised for the synthesis of important materials across the broad spectrum of chemical industries. Accessing highly substituted derivatives can often be difficult as their functionalizations are generally performed via electrophilic aromatic substitution, SEAr. Here we provide an alternative and mechanistically distinct approach whereby aromatic aldehydes are assembled from saturated precursors via a desaturative process. This novel strategy harnesses the high‐fidelity of Diels–Alder cycloadditions to quickly construct multi‐substituted cyclohexenecarbaldehyde cores which undergo desaturation via the synergistic interplay of enamine, photoredox and cobalt triple catalysis.

Strategies and Mechanisms of First-Row Transition Metal-Regulated Radical C–H Functionalization

“…In addition, Leonori's group found that a synergistic combination of morpholine, photoredox conditions and Co catalysis could transform saturated cyclohexane formaldehyde into an aromatic aldehyde through the same Co-regulated radical mechanism (Scheme 45f). 373 Very recently, Zuo's group demonstrated Co/bisphosphonium-catalyzed the selective C(sp 3 )−H dehydrogenation of benzylic alcohols (45-34) (Scheme 45g). 374 The photocatalytic system demonstrated high efficiency when applied in continuous-flow conditions, even using a straightforward and readily assembled continuous-flow setup.…”

Light-driven C–O coupling of carboxylic acids and alkyl halides over a Ni single-atom catalyst

“…4,5 The renewed interest in this catalytic methodology is owed to the mild reaction conditions employed, the robust functional group tolerance, and the possibility to access redox-neutral reaction routes unattainable with classical ionic chemistry triggered by thermal activation. 6,7 Besides, the use of visible light is seen as an ideal driving force for catalytic transformations, [8][9][10][11][12][13][14] in order to establish a greener chemical industry within the forthcoming decarbonization of our economy. 15 Despite the novelty of the approach, the method relies on the use of Ir or Ru-containing photocatalysts (chiefly, Ir[dF(CF3)ppy]2(dtbbpy)PF6 or Ru[dF(CF3)ppy]2(dtbbpy)PF6, where (dF(CF3)ppy = 2-(2,4difluorophenyl)-5-(trifluoromethyl)pyridine, and dtbbpy = 4,4′-di-tert-butyl-2,2'-bipyridine)), homogeneous Ni co-catalysts, and additional bipyridyl compounds for ligating the Ni centers, as summarized in Fig.…”