A Pd-catalyzed amide-directed enantioselective hydrocarbofunctionalization of unactivated alkenes with C-H nucleophiles has been developed using a chiral monodentate oxazoline (MOXin) ligand. Various indoles react at C3 position with aminoquinoline-coupled 3-alkenamides to give γ addition products in good to excellent yield and enantioselectivity. This study represents an important advance of the development of chiral monodentate oxazoline ligands, which have been underexplored for asymmetric catalysis.
A Pd-catalyzed carboxamide-directed enantioselective 1,2-carboboration reaction of unactivated alkenes with C−H nucleophiles and B 2 Pin 2 has been developed using a second generation of chiral monodentate oxazoline (MOXca) ligand. The MOXca ligand featuring a modular design of a Nlinked carbazole side arm can be readily synthesized from serine and NH-carbazoles and provided further improved enantiocontrol of the AQ-directed nucleopalladation over MOXin ligand. The use of KTFA additive and TFE solvent was critical to obtain high reactivity in this difunctionalization reaction system. Preliminary study showed that 1,2-aminoboration of 3-butenamide with imide N-nucleophiles and B 2 Pin 2 under the same conditions proceeded in good yield and high enantioselectivity.
Intramolecular cyclization of nitrogen-containing molecules onto pendant alkenes is an efficient strategy for the construction of N-heterocycles, which are of paramount importance in, for example, pharmaceuticals and materials. Similar intermolecular cyclization reactions, however, are scarcer for nitrogen building blocks, including N-centred radicals, and divergent and modular versions are not established. Here we report the use of sulfilimines as bifunctional N-radical precursors for cyclization reactions with alkenes to produce N-unprotected heterocycles in a single step through photoredox catalysis. Structurally diverse sulfilimines can be synthesized in a single step, and subsequently engage with alkenes to afford synthetically valuable five-, six- and seven-membered heterocycles. The broad and diverse scope is achievable by a radical-polar crossover annulation enabled by the bifunctional character of the reagents, which distinguishes itself from all other N-centred-radical-based reactions. The modular synthesis of the sulfilimines allows for larger structural diversity of N-heterocycle products than is currently achievable with other single cyclization methods.
An enantioselective addition reaction of various alkyl groups to
unactivated internal alkenes under Cu catalysis has been developed.
The reaction uses amide-linked aminoquinoline as the directing group,
4-alkyl Hantzsch esters as the donor of alkyl radicals, and rarely
used biaryl diphosphine oxide as a chiral ligand. β-lactams
featuring two contiguous stereocenters at Cβ and the β
substituent can be obtained in good yield with excellent enantioselectivity.
Mechanistic studies indicate that a nucleophilic addition of the alkyl
radical to CuII-coordinated alkene is the enantio-determining
step.
A Pd-catalyzed carboxamide-directed hydrocarbofunctionalization
reaction of unactivated alkenes with different alkynes has been developed.
An 8-aminoquinoline auxiliary was utilized to increase the reactivity
of the alkene and control the regioselectivity via the formation of
thermodynamically favored five-membered palladacycle intermediate.
3-Alkene carboxamides bearing a C4-substituted alkene group reacted
with a variety of terminal alkynes in the presence of an ortho-phenyl benzoic acid promoter, yielding γ-alkynylated products
with high yields and regioselectivity. 3-Butenamide underwent a three-component
coupling reaction with internal alkynes and carboxylic acids to give
vinyl ester products. Preliminary mechanistic studies indicate that
the intramolecular migratory insertion of alkynyl or vinyl palladium
species into the CC bond is responsible for the γ-selective
alkynylation or alkenylation of the alkene group.
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