Furfural and related compounds are industrially relevant building blocks obtained from lignocellulosic biomass. To enhance the added value of these renewable resources, a Ru-catalyzed hydrofurylation of alkenes, involving a directed C-H activation at C3 of the furan ring, was developed. A thorough experimental study revealed that a bidentate amino-imine directing group enabled the desired coupling. Removal of the directing group occurred during the purification step, directly releasing the C3-functionalized furfurals. Development of the reaction as well as optimization and scope of the method were described. A mechanism was proposed on the basis of DFT calculations.
The
direct introduction of sp3 carbon fragments at the
β position of α,β-unsaturated aldehydes is greatly
complicated by competing 1,2-addition manifolds. Previous catalytic
enantioselective conjugate addition methods, based on the use of organometallic
reagents or ground-state iminium ion activation, could not provide
general and efficient solutions. We report herein that, by turning
them into strong oxidants, visible light excitation of chiral iminium
ions triggers a stereocontrolled radical pathway that exclusively
affords highly enantioenriched β-substituted aldehydes bearing
a variety of alkyl fragments.
Reported herein is a dual nickel-and photoredox-catalysed modular approach for the preparation of enantioenriched N-benzylic heterocycles. α-Heterocyclic carboxylic acids, easily obtainable from common commercial material, are reported as suitable substrates for a decarboxylative strategy in conjunction with a chiral pyridine-oxazoline (PyOx) ligand, providing quick access to enantioenriched drug-like products. The presence of a directing group on the heterocyclic moiety is shown to be beneficial, affording improved stereoselectivity in a number of cases.
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