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Creators/Authors contains: "Warren, Timothy H."

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  1. The methyl moiety is a key functional group that can result in major improvements in the potency and selectivity of pharmaceutical agents. We present a radical relay C–H methylation methodology that employs a β-diketiminate copper catalyst capable of methylating unactivated C(sp3)–H bonds. Taking advantage of the bench-stable DABAL-Me3, an amine-stabilized trimethylaluminum reagent, methylation of a range of substrates possessing both activated and unactivated C(sp3)–H bonds proceeds with a minimal amount of overmethylation. Mechanistic studies supported by both experiment and computation suggest the intermediacy of a copper(II) methyl intermediate reactive toward both the loss of the methyl radical as well capture of radicals R• to form R–Me bonds. 
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  2. Commercially available benzophenone imine (HNCPh 2 ) reacts with β-diketiminato copper( ii ) tert -butoxide complexes [Cu II ]–O t Bu to form isolable copper( ii ) ketimides [Cu II ]–NCPh 2 . Structural characterization of the three coordinate copper( ii ) ketimide [Me 3 NN]Cu–NCPh 2 reveals a short Cu-N ketimide distance (1.700(2) Å) with a nearly linear Cu–N–C linkage (178.9(2)°). Copper( ii ) ketimides [Cu II ]–NCPh 2 readily capture alkyl radicals R˙ (PhCH(˙)Me and Cy˙) to form the corresponding R–NCPh 2 products in a process that competes with N–N coupling of copper( ii ) ketimides [Cu II ]–NCPh 2 to form the azine Ph 2 CN–NCPh 2 . Copper( ii ) ketimides [Cu II ]–NCAr 2 serve as intermediates in catalytic sp 3 C–H amination of substrates R–H with ketimines HNCAr 2 and t BuOO t Bu as oxidant to form N -alkyl ketimines R–NCAr 2 . This protocol enables the use of unactivated sp 3 C–H bonds to give R–NCAr 2 products easily converted to primary amines R–NH 2 via simple acidic deprotection. 
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  7. Abstract

    S‐Nitrosothiols (RSNOs) serve as air‐stable reservoirs for nitric oxide in biology. While copper enzymes promote NO release from RSNOs by serving as Lewis acids for intramolecular electron‐transfer, redox‐innocent Lewis acids separate these two functions to reveal the effect of coordination on structure and reactivity. The synthetic Lewis acid B(C6F5)3coordinates to the RSNO oxygen atom, leading to profound changes in the RSNO electronic structure and reactivity. Although RSNOs possess relatively negative reduction potentials, B(C6F5)3coordination increases their reduction potential by over 1 V into the physiologically accessible +0.1 V vs. NHE. Outer‐sphere chemical reduction gives the Lewis acid stabilized hyponitrite dianiontrans‐[LA‐O‐N=N‐O‐LA]2−[LA=B(C6F5)3], which releases N2O upon acidification. Mechanistic and computational studies support initial reduction to the [RSNO‐B(C6F5)3] radical anion, which is susceptible to N−N coupling prior to loss of RSSR.

     
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