Gold-catalyzed regioselective oxidation of propargylic carboxylates: a reliable access to α-carboxy-α,β-unsaturated ketones/aldehydes

Controlling Selectivity in Shuttle Hetero-difunctionalization Reactions: Electrochemical Transfer Halo-thiolation of Alkynes

Shuttle hetero-difunctionalization reaction, in which two chemically distinct functional groups are transferred between two molecules, has long been an unmet goal due to the daunting challenges in controlling the chemo-, regio-, and stereoselectivity. Herein, we disclose an electrochemistry enabled shuttle reaction (e-shuttle) to selectively transfer one RS^- and one X^- group between β-halosulfides and unsaturated hydrocarbons via a consecutive paired electrolysis mechanism. The preferential anodic oxidation of one anion over the other, which is controlled by their distinct redox potentials, plays a pivotal role in controlling the high chemoselectivity of the process. This easily scalable methodology enables the construction of a myriad of densely functionalized β-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g., 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS-Br reagents. In a broader context, these results open up new strategies for selective shuttle difunctionalization reactions.

Gold(i)-catalyzed 6-endo-dig azide–yne cyclization: efficient access to 2H-1,3-oxazines

Denitrogenative 6-endo-dig azide–yne cyclization of α-propargyloxy-β-haloalkylazides was enabled by gold catalysis, thus providing 2H-1,3-oxazines.

Palladium-Catalyzed Oxidative Synthesis of α-Acetoxylated Enones from Alkynes

We report a palladium-catalyzed oxidative functionalization of alkynes to generate α-acetoxylated enones in one step. A range of functional groups are well-tolerated in this reaction. Mechanistic studies, including the use of (18) O-labeled DMSO, revealed that the ketone oxygen atom in the product originates from DMSO.

Gold-Catalyzed Ring Expansion of Alkynyl Heterocycles through 1,2-Migration of an Endocyclic Carbon-Heteroatom Bond

A mild and efficient gold-catalyzed oxidative ring-expansion of a series of alkynyl heterocycles using pyridine-N-oxide as the oxidant has been developed, which affords highly valuable six- or seven-membered heterocycles with wide functional group toleration. The reaction consists of a regioselective oxidation and a chemoselective migration of an endocyclic carbon-heteroatom bond (favored over C-H migration) with the order of migratory aptitude for carbon-heteroatom bonds being C-S>C-N>C-O. In the absence of an oxidant, polycyclic products are readily constructed through a ring-expansion/Nazarov cyclization reaction sequence.

Gold-catalyzed selective oxidation of 4-oxahepta-1,6-diynes to 2H-pyran-3(6H)-ones and chromen-3(4H)-ones via β-gold vinyl cation intermediates

α-Oxo gold carbenes generated in situ via the gold-catalyzed selective oxidation of 4-oxahepta-1,6-diynes were effectively trapped by internal alkynes, resulting in the formation of 2H-pyran-3(6H)-ones, 3, and chromen-3(4H)-ones, 4, upon facile trapping the vinyl cation intermediates.

Assigning regioisomeric or diastereoisomeric relations of problematic trisubstituted double-bonds through heteronuclear 2D selective J-resolved NMR spectroscopy

Although one of the first 2D NMR methods, but so far neglected, selectiveJ-resolved NMR spectroscopy offers a unique opportunity to help organic chemists in structure elucidation, avoiding natural and non-natural product misassignments.

Expanding the horizon of intermolecular trapping of in situ generated α-oxo gold carbenes: efficient oxidative union of allylic sulfides and terminal alkynes via C-C bond formation

With a new P,S-bidentate phosphine as the ligand to gold(I), the α-oxo gold carbenes generated in situ via gold-catalyzed intermolecular oxidation of terminal alkynes were effectively trapped by various allylic sulfides, resulting in the formation of α-aryl(alkyl)thio-γ,δ-unsaturated ketones upon facile [2,3]sigmatropic rearrangements.

Gold-Catalyzed Oxidation of Propargylic Ethers with Internal C-C Triple Bonds: Impressive Regioselectivity Enabled by Inductive Effect

Inductive perturbations of C-C triple bonds are shown to dictate the regiochemistry of gold-catalyzed oxidation of internal C-C triple bonds in the cases of propargylic ethers, resulting in highly regioselective formation of β-alkoxy-α,β-unsaturated ketones (up to >50/1 selectivity) via α-oxo gold carbene intermediates. Ethers derived from primary propargylic alcohols can be reliably transformed in good yields, and various functional groups are tolerated. With substrates derived from secondary propargylic alcohols, the development of a new P,N-bidentate ligand enables the minimization of competing alkyl group migration to the gold carbene center over the desired hydride migration; the preferred migration of a phenyl group, however, results in efficient formation of a α-phenyl-β-alkoxy-α,β-unsaturated ketone. These results further advance the surrogacy of a propargyl moiety to synthetically versatile enone function with reliable and readily predictable regioselectivity.