Light-Driven Carbon–Carbon Coupling of α-sp³–CH of Aliphatic Alcohols with sp²–CH Bond of 1,4-Naphthoquinones

Abstract

Here, an α-selective Csp3–H bond functionalization of primary aliphatic alcohols with 1,4-naphthoquinones yielded Csp2 –Csp2 coupled products driven by blue-LED light under catalyst, metal, base, and reagent-free conditions. In this transformation, cleavage of three C–H bonds (two sp3–C-H, one sp2–C–H, and one O–H) and four new bonds formed, leading to fluorescent 2-acylated-1,4-naphthohydroquinones.

Synthesis and Photochemical Properties of Fluorescent Metabolites Generated from Fluorinated Benzoylmenadiones in Living Cells

“…On the other hand, α-selective Csp 3 –H bond functionalization of primary aliphatic alcohols with 1,4-naphthoquinones driven by blue LED light irradiation in the absence of a catalyst, metal, base, or reagent afforded a large series of 2-acylated-1,4-naphthohydroquinones that were shown to display a fluorescent signal in the visible region (Figure ). For example, the maxima of absorption (λ abs ) and of emission (λ em ) were found to be 393 and 516 nm, respectively, for 2-acetyl-1,4-naphthohydroquinone in acetonitrile, substantiating our preliminary findings (Figure ).…”

Blue Light Irradiated Metal-, Oxidant-, and Base-Free Cross-Dehydrogenative Coupling of C(sp2)–H and N–H Bonds: Amination of Naphthoquinones with Amines

“…In the case of aminols also, selective C­( sp 2 )–N coupling was realized within 30 min and intermolecular or intramolecular C–C/O coupling was not observed even after exposing the reaction for a longer duration (Scheme ). Selective coupling of the N–H bond over the −OH bond of aminols could be due to the lower bond dissociation enthalpy of the N–H (<90 kcal/mol) bond than α-C–H and O–H bonds (>110 kcal/mol) . Subsequently, an array of aliphatic aminols, 2-aminoethanol, 3-aminopropanol, 4-aminobutanol, and 5-aminopentanol, were explored for C2-amination of naphthoquinone to get respective 2-(hydroxyalkyl) amino-1,4-naphthoquinone 52 – 55 with 92–96% yields within 30 min.…”

“…Recently, our group has embarked on the light-driven construction of carbon–carbon and carbon–heteroatom bonds for the preparation of biologically relevant organic molecules. − Very recently, light-driven C­( sp 2 )–C­( sp 3 ) bond formation between 1,4-naphthoquinones and primary aliphatic alcohols has been achieved for the preparation of 2-acylated-1,4-naphthoquinones in moderate to good yields . Furthermore, the reaction needed a substoichiometric amount of naphthoquinone as an oxidant.…”

“…Despite the involvement of radicals in preliminary steps, C–N coupling was furnished by an ionic pathway and the direct coupling of carbon and nitrogen centered radicals could not be achieved by us. Here, in continuation of our work on light-irradiated coupling reactions, − we disclose an attractive mild blue light irradiated coupling of C–H and N–H bonds for the C2-amination of 1,4-naphthoquinones and quinones with a diverse array of commercially available amines in methanol by dehydrogenative pathways. Furthermore, UV–visible, kinetic isotopic effect (KIE), and controlled experiments studies have been conducted to establish the mechanism of the blue light irradiated reaction.…”

Visible-Light-Promoted Desulfurization to Synthesize Deoxyglycosides

“…The 2-SAc glycosyl donors can be efficiently prepared starting from free methyl glycosides by combining selective protection strategies and thioacetate-involved substitution strategies. − However, this desulfurization has to be performed in a dedicated photochemical reactor, and, in some cases, the high-energy UV light can induce the formation of undesired byproducts. For example, under UV irradiation, desulfurization of per-acetylated glycosyl 1-thiols may produce acetyl migration byproducts caused by β-(acyloxy)­alkyl radical rearrangement, ,, and desulfurization of substrates containing benzyl-type protecting groups may also produce unknown byproducts. , A reaction under visible-light irradiation is usually milder, in which a photocatalyst has to be employed to transfer energy from the light to the substrate. − The desulfurization of cysteinyl peptide under visible light has been reported by Guo’s group for the synthesis of peptides through the ligation-desulfurization protocol . Thus, in this study, we developed a visible-light-induced desulfurization method (Scheme b) to synthesize deoxyglycosides as an alternative to UV-light-induced desulfurization.…”