Synthesis of π-Extended Imidazo[1,2-]quinolines via Carboxylic Acid-Assisted Ru(II)-Catalyzed Dual C-H Activation and Alkyne Annulation.

Ru(II)-catalyzed, carboxylic acid-assisted oxidative annulation of -aryl azoles with alkynes via double C-H activation to produce highly functionalized π-extended imidazo[1,2-]quinolines is reported. The reaction features a broad substrate generality and tolerates various biologically relevant scaffolds. Interestingly, annulated products showed strong fluorescence properties and an AgIE effect and exhibited a selective fluorescent response toward the Cu ion.

Cyclometalated Ruthenium-Complex-Catalyzed Selective Oxidation of Olefins to Carbonyls.

Cyclometalated ruthenium(II)-complex-catalyzed selective oxidative scission of olefins to carbonyls is described. A strong C-donor ligand, paired with a rigid backbone and redox activity of ruthenium, provided high catalytic activity and a long lifetime for olefin oxidation. The catalyst tolerates numerous functional groups and applies to challenging biomass-, natural-product-, sugar-, amino-acid-, and fatty-acid-derived substrates.

Parts-Per-Million Level Loading Cyclometalated Ru(II)-NHC Catalyzed Selective Oxidation of Olefins to Carbonyls.

Oxidative cleavage of olefins is a useful reaction in organic synthesis. The most well-known catalytic system is the osmium based Lemieux-Johnson catalyst, which generally requires high catalyst loading and tends to suffer from rapid overoxidation to produce the acid predominantly. Hence, the development of a mild, general, and selective method toward the oxidative cleavage of alkenes to carbonyl compounds is highly desired.

Ru/O-Catalyzed Oxidative C-H Activation/Alkyne Annulation Using Quinoline-Functionalized NHC as a Directing and Functionalizable Group.

The ruthenium/O-catalyzed oxidative annulation reaction of imidazo[1,5-]quinolin-2-ium salts with alkynes -heterocyclic carbene-directed C-H activation to obtain π-conjugated fused imidazo[1,5-]quinolin-2-ium derivatives is reported. Molecular oxygen has been explored as an economic and clean oxidant and an alternative to metal oxidants. The current protocol exhibits a wide range of substrate scope including bioactive (±)-α-tocopherol derivatives.

Ruthenium(II)-Catalyzed Oxidative Annulation of Imidazo[1,5-a]quinolin-2-iums Salts and Internal Alkynes via C-H Bond Activation.

Ruthenium(II)-catalyzed synthesis of π-conjugated fused imidazo[1,5-a]quinolin-2-ium derivatives have been achieved via C-H activation of quinoline-functionalized NHC (NHC=N-heterocyclic carbene) and oxidative coupling with internal alkynes. The reaction occurred with high efficiency, broad substrate scope, tolerates a wide range of functional groups and utilized into a gram-scale. Synthetic applications of the coupled product have been exemplified in the late-stage derivatization of various highly functionalized scaffolds.

Copper-Catalyzed Oxidative Dehydrogenative Reaction of Quinoline--Oxides with Donor-Acceptor Cyclopropanes: Installation of a Tertiary Alkyl Motif at C2 Position.

A copper-catalyzed oxidative dehydrogenative reaction of quinoline -oxides with donor-acceptor cyclopropanes has been demonstrated to construct C2-alkylated quinolines containing a γ-keto diester motif. The use of molecular oxygen as an oxidant, excellent site-selectivity, and good functional group tolerance are the important features in this process. The preliminary mechanistic studies demonstrate that the catalyst plays a dual role as a Lewis acid and a redox catalyst.

Site-Selective Deoxygenative Amination of Azine -Oxides with Carbodiimides under Catalyst-, Activator-, Base-, and Solvent-Free Conditions.

An operationally simple method for synthesizing 2-amino azines [3+2] dipolar cycloaddition of azine -oxide with carbodiimide has been demonstrated. The reaction can proceed smoothly under simple heating conditions without any transition metal catalyst, activator, base, and solvent. This transformation demonstrates a broad substrate scope and produces CO as the only co-product.

Boric acid catalyzed chemoselective reduction of quinolines.

Boric acid promoted transfer hydrogenation of substituted quinolines to synthetically versatile 1,2,3,4-tetrahydroquinolines (1,2,3,4-THQs) was described under mild reaction conditions using a Hantzsch ester as a mild organic hydrogen source. This methodology is practical and efficient, where isolated yields are excellent and reducible functional groups are well tolerated in the N-heteroarene moiety. The reaction parameters and tentative mechanistic pathways are demonstrated by various control experiments and NMR studies.