Browsing by Author "Ascenzi Pettenuzzo, Cristina"

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    Photoinduced Pyridine N-Oxide Catalyzed Functionalization of Unactivated Olefins and Alkylboronic Acids
    (2024-12) Ascenzi Pettenuzzo, Cristina; Deng, Yongming; Minto, Robert; Laulhé, Sébastien; Sardar, Rajesh
    Primary alcohols are fundamental substrates in organic synthesis, and widely used in pharmaceutical, agrochemical, and bulk/fine chemical industries. Chapter one describes the current practices in industry and discoveries in academia for primary aliphatic alcohol synthesis. The methods discussed in chapter one include hydroboration-oxidation, the Ziegler process, hydroformylation/hydrogenation, transition metal-catalyzed hydrogenation of epoxides. Catalytic methods are described as well, both in transition metal catalysis and photoredox catalysis. Chapter two introduces a photoinduced pyridine N-oxide-catalyzed method for carbohydroxylation of unactivated olefins. The extensive reaction optimization process is shown, including the screening of different pyridine N-oxides, photocatalysts, and solvents. In this chapter, the applicability of the method is confirmed for a broad scope of unactivated olefins, both mono- and di-substituted. The regioselectivity of the transformation is confirmed by X-ray crystallography. Chapter three offers mechanistic insights regarding the carbohydroxylation of unactivated olefins. The proposed mechanism is corroborated through different experiments. Cyclic voltammetry and Stern-Volmer fluorescence quenching analysis, revealed that the photocatalyst directly oxidized pyridine N- oxide but does not oxidize the olefin substrate. The substitution step that ultimately affords the primary alcohol is confirmed with the use of different oxygen nucleophiles, that generate the corresponding carbo-oxygenated products. The 18O labeling experiments provide solid evidence that the oxygen source is not the pyridine N-oxide, rather it is the added nucleophile. Radical trapping experiments confirm the existence of the carbon radical generated, after pyridine N-oxy radical addition to the olefin. Chapter four delves in the development of a protocol for the generation of alkyl carbon radicals from alkylboronic acids, wherein photoexcited 4-nitropyridine N-oxide biradical features a catalyst to promote the nucleo-homolytic substitution of boronic acids. With a wide range of readily available aliphatic boronic acids, including methyl boronic acid, the developed catalytic system demonstrates broad applicability for alkylation, amination, and cyanation.
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    Photoredox/Pyridine N-Oxide Catalyzed Carbohydroxylation and Aminohydroxylation of α-Olefins
    (ACS, 2025) Ascenzi Pettenuzzo, Cristina; Pradhan, Deepak Ranjan; Singh, Jujhar; Liu, Lichuan; Cuffel, Gabe; Vetticatt, Mathew J.; Deng, Yongming; Chemistry and Chemical Biology, School of Science
    Regioselective carbohydroxylation and aminohydroxylation of α-olefins were developed by a photoredox catalyst and pyridine N-oxide. This approach offers the catalytic and direct conversion of unactivated alkenes to a series of primary alcohols, including those bearing β-quaternary carbon centers and β-amino alcohols. The regioselective difunctionalization is enabled by the radical addition of α-olefin from the pyridine N-oxy radical, which is generated from readily available pyridine N-oxide via photoredox catalyzed single-electron oxidation. A combination of experimental and computational mechanistic studies was employed to lend support for the proposed reaction mechanism that proceeds via interwoven radical steps and polar substitution. The implications of this method for regioselective difunctionalization of α-olefins were further demonstrated by the examples of carboetherification, carboesterification, and lactone formation.