Lingheng Kong

Redox-Neutral Couplings between Amides and Alkynes via Cobalt(III)-Catalyzed C–H Activation

C-H activation assisted by a bifunctional directing group has allowed the construction of heterocycles. This is ideally catalyzed by earth-abundant and eco-friendly transition metals. We report Co(III)-catalyzed redox-neutral coupling between arenes and alkynes using an NH amide as an electrophilic directing group. The redox-neutral C-H activation/coupling afforded quinolines with water as the sole byproduct.

Cobalt(III)-Catalyzed C–C Coupling of Arenes with 7-Oxabenzonorbornadiene and 2-Vinyloxirane via C–H Activation

Co(III)-catalyzed mild C-C couplings of arenes with strained rings such as 7-oxabenzonorbornadienes and 2-vinyloxirane have been realized. The transformation is proposed to undergo ortho C-H activation, olefin insertion, and subsequent β-oxygen elimination. A broad range of synthetically useful functional groups are compatible, thus providing a new entry to access diversely 2-functionalized indoles.

Access to Structurally Diverse Quinoline-Fused Heterocycles via Rhodium(III)-Catalyzed C–C/C–N Coupling of Bifunctional Substrates

Rhodium(III)-catalyzed C-H activation of heteroarenes and functionalization with bifunctional substrates such as anthranils allows facile construction of quinoline-fused heterocycles under redox-neutral conditions. The couplings feature broad substrate scope and provide step-economical access to two classes of quinoline-fused condensed heterocycles.

Cobalt(III)-catalyzed efficient synthesis of indenones through carboannulation of benzoates and alkynes

Cobalt(III)-catalyzed C–H activation of simple benzoate esters has been achieved, and redox-neutral annulative coupling with internal alkynes allowed efficient synthesis of indenones. The employment of the weak and simple ester directing group makes it an attractive protocol in carbocycle synthesis.

Rhodium(III)-Catalyzed Synthesis of Naphthols via C–H Activation of Sulfoxonium Ylides

Direct and efficient synthesis of 1-naphthols has been realized via Rh(III)-catalyzed C-H activation of sulfoxonium ylides and subsequent annulation with alkynes, where the sulfoxonium ylide functioned as a new traceless bifunctional directing group. This reaction occurred under redox-neutral conditions with a broad substrate scope.

Rhodium(III)-Catalyzed Regio- and Stereoselective C–H Allylation of Arenes with Vinyl Benzoxazinanones

Vinyl benzoxazinanone was applied as an electrophilic allylating reagent for a series of arenes under redox-neutral Rh(III) catalysis. This reaction occurs in high efficiency under mild conditions to afford allylarenes bearing a sulfonamide functionality in exclusively E-selectivity. This allylation system combines C-H activation of arenes and scission of an unstrained six-membered ring.

Rh(III)-catalyzed coupling of nitrones with alkynes for the synthesis of indolines

Abstract Rh-catalyzed redox-neutral coupling between N-aryl nitrones and alkynes has been achieved under relatively mild conditions. The reaction proceeded via C–H activation at the N-aryl ring with subsequent O-atom transfer, affording trisubstituted indolines in good chemoselectivity and moderate to good diasteroselectivity.

Rhodium(III)-Catalyzed Acylation of C(sp3)–H Bonds with Cyclopropenones

Rh(III)-catalyzed activation and acylation of sp3 C-H bonds has been realized with diarylcyclopropenone as an acylating reagent. Both benzylic C-H in 8-methylquinolines and unactivated C-H in 2-alkylpyridines are applicable in this C-H acylation reaction, providing enones in good yields under redox-neutral conditions.

Access to Substituted Propenoic Acids via Rh(III)-Catalyzed C–H Allylation of (Hetero)Arenes with Methyleneoxetanones

An efficient synthesis of disubstituted acrylic acids has been realized via Rh(III)-catalyzed C-H activation of (hetero)arenes and coupling with four-membered methyleneoxetanones under redox-neutral conditions. In most cases, the reactions are silver-free, and the products are exclusively E-selective with a broad substrate scope. The transformation proceeds via ortho C-H activation followed by selective olefin insertion and β-oxygen elimination.

Ruthenium(II)-catalyzed α-fluoroalkenylation of arenes via C–H bond activation and C–F bond cleavage

Ru(II)-Catalyzed efficient α-fluoroalkenylation of arenes has been realized with gem-difluorostyrene as an olefinating reagent. This coupling system is efficient with a broad substrate scope, providing 1,2-diaryl-substituted monofluoroalkenes with good to excellent regio- and stereoselectivities under silver-free conditions.