Aerobic Linear Allylic C–H Amination: Overcoming Benzoquinone Inhibition

Abstract

An efficient aerobic linear allylic C—H amination reaction (LAA) is reported under Pd(II)/bis-sulfoxide/Brønsted base catalysis. The reaction operates under preparative, operationally simple conditions (1 equiv. olefin, 1 atm. O2 or air), with reduced Pd(II)/bis-sulfoxide catalyst loadings while providing higher turnovers and product yields than systems employing stoichiometric benzoquinone (BQ) as the terminal oxidant. Palladium(II)/benzoquinone π-acidic interactions have been invoked in various catalytic processes and are often considered beneficial in promoting reductive functionalizations. When such electrophilic activation for functionalization is not needed, however, benzoquinone at high concentrations may compete with crucial ligand (bis-sulfoxide) binding and inhibit catalysis. Kinetic studies reveal an inverse relationship between the reaction rate and the concentration of BQ, suggesting that benzoquinone is acting as a ligand for Pd(II) which results in an inhibitory effect on catalysis.

Enantioselective Allylic C−H Oxidation of Terminal Olefins to Isochromans by Palladium(II)/Chiral Sulfoxide Catalysis

“…Notably, examination of the phosphoramidite ( S )‐ L11 under both our standard conditions and O 2 ‐free conditions previously reported resulted in trace formation of 2 a (entry 15). Replacing the sterically‐bulky 2,6‐dimethylbenzoquinone (2,6‐DMBQ) with BQ as the stoichiometric oxidant diminished enantioselectivity (entry 16), possibly because of an undesirable competition between BQ and ( S , R )‐ tBu‐ArSOX L7 as a ligand for palladium(II) …”

Palladium‐Catalyzed Oxidation Reactions of Alkenes with Green Oxidants

“… Conversion of allyl moieties by the groups of a) Stahl [from Refs. (top) and (bottom)], b) Grubbs, c) Bäckvall, d) Hull, and e) White . TFA=trifluoroacetate, NMP= N ‐methyl‐2‐pyrrolidone, BQ=1,4‐benzoquinone, pc=phthalocyanine, DHBQ=2,5‐dihydroxy‐1,4‐benzoquinone.…”

“…The well-known Ts uji-Trost reactioni sapowerful strategy for the transformation of allyl moieties; however,t he prefunc-tionalization of substrates limits its application.M oreover,c ontrol of the selectivity during palladium-catalyzed oxidative functionalization of allyl moieties remains ac hallenging research topic. [40] For the use of O 2 in the conversiono fa llyl moieties, the groupso fS tahl, [41] Grubbs, [42] Bäckvall, [43] Hull, [44] and White [45] have performed much groundbreaking work (Scheme 27). Since 2014, we have also successively developed as eries of aerobico xidative allylic CÀHf unctionalizations of alkenes, withO 2 as the sole oxidant participating in the cycle (Scheme 28).…”

“…Conversion of allyl moieties by the groups of a) Stahl [from Refs. [41a] (top) and [41b] (bottom)],b)Grubbs,[42] c) Bäckvall,[43] d) Hull,[44] and e) White [45]. TFA = trifluoroacetate, NMP = N-methyl-2-pyrrolidone,B Q= 1,4-benzoquinone, pc = phthalocyanine, DHBQ = 2,5-dihydroxy-1,4-benzoquinone.ChemSusChem 2019ChemSusChem , 12,2911ChemSusChem -2935 www.chemsuschem.org 2019 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim…”

Transition-Metal-Free C(sp3)–H Oxidation of Diarylmethanes

“…Therefore, transition-metal-free methods for oxidation of alkylarenes are desirable in the pharmaceutical industry which can avoid the use of the heavy metal. For oxidation process, Molecular oxygen (O 2 ) represents one of the best choices because of its low cost and has attracted substantial attention [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Herein, we wish to report the direct oxidation of diarylmethanes to diaryl ketones using O 2 -mediation by MN(SiMe 3 ) 2 [M = K, Na or Li], which represent a green and efficient synthetic method for this transformation.…”