We report that Ni(COD)(DQ) (COD = 1,5-cyclooctadiene, DQ = duroquinone), an air-stable 18-electron complex originally described by Schrauzer in 1962, is a competent precatalyst for a variety of nickel-catalyzed synthetic methods from the literature. Due to its apparent stability, use of Ni(COD)(DQ) as a precatalyst allows reactions to be conveniently performed without use of an inert-atmosphere glovebox, as demonstrated across several case studies. Scheme 1. Overview of the growing nickel precatalyst toolkit.
A palladium(II)‐catalyzed enantioselective α‐alkylation of azlactones with nonconjugated alkenes is described. The reaction employs a chiral BINOL‐derived phosphoric acid as the source of stereoinduction, and a cleavable bidentate directing group appended to the alkene to control the regioselectivity and stabilize the nucleopalladated alkylpalladium(II) intermediate in the catalytic cycle. A wide range of azlactones were found to be compatible under the optimal reaction conditions to afford products bearing α,α‐disubstituted α‐amino‐acid derivatives with high yields and high enantioselectivity.
An asymmetric 1,2-dicarbofunctionalization of unactivated
alkenes
with aryl iodides and aryl/alkenylboronic esters under nickel/bioxazoline
catalysis is disclosed. A wide array of aryl and alkenyl nucleophiles
are tolerated, furnishing the products in good yield and with high
enantioselectivity. In addition to terminal alkenes, 1,2-disubstituted
internal alkenes participate in the reaction, establishing two contiguous
stereocenters with high diastereoselectivity and moderate enantioselectivity.
A combination of experimental and computational techniques shed light
on the mechanism of the catalytic transformation, pointing to a closed-shell
pathway with an enantiodetermining migratory insertion step, where
stereoinduction arises from synergistic interactions between the sterically
bulky achiral sulfonamide directing group and the hemilabile bidentate
ligand.
Diarylation of alkenyl sulfonamides with aryl iodides and aryl boronic esters under nickel catalysis is reported. The developed method tolerates coupling partners with disparate electronic properties and substitution patterns. 1,2-and 1,1-Disubstituted alkenes, as well as alkenes distal from the directing group, are all accommodated. Control experiments are consistent with a N-Ni coordination mode of the directing group, which stands in contrast to earlier reports on amide-directed 1,2-diarylation that involve carbonyl coordination. The synthetic utility of the method arises from the dual function of the sulfonamide as both a directing group and masked amine nucleophile. This is highlighted by various product diversifications where complex amine compounds are synthesized in a two-step sequence of N-functionalization and deprotection of the sulfonyl group. File list (4) download file view on ChemRxiv Manuscript.pdf (632.65 KiB) download file view on ChemRxiv Supporting Info.pdf (21.57 MiB) download file view on ChemRxiv 2a.cif (407.62 KiB) download file view on ChemRxiv 2ab.cif (0.98 MiB)
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