Rhodium(III)‐Catalyzed Regioselective C−H Activation/Annulation for the Diverse Pyrazole‐Core Substituted Furans

Abstract

A novel and facile regioselective synthetic method for polyfunctionalized furans involving rhodium (III)-catalyzed pyrazole-or indazole-directed dual CÀ H functionalization with diazodicarbonyls has been developed. This strategy provides rapid access to diverse tetrasubstituted furans bearing various pyrazoles or indazoles. This unprecedented one-pot protocol proceeds via cascade CÀ H activation, metal-carbene formation, migratory insertion, intramolecular cyclization, and deprotonation. Ethyl 4-((1H-pyrazol-1-yl)methyl)-2-(4-methoxyphenyl)-5phenylfuran-3-carboxylate (3 j). Yellow liquid; yield -69 mg; HRMS (EI + ): m/z: calcd for C 24 H 22 N 2 O 4 : 402.1580, Found: 402.1581.Ethyl 4-((1H-pyrazol-1-yl)methyl)-2-(4-nitrophenyl)-5-phenylfuran-3-carboxylate (3 k). Yellow solid; yield -69 mg; 83%; mp 99-100°C; IR (KBr): v˜= H NMR (600 MHz, CDCl 3 ): δ = 8.27 (d, J = 9.6 Hz, 2H), 8.06 (d, J = 9.6 Hz, 2H), 7.78 (d, J = 7.2 Hz, 2H), 7.57 (d, J = 1.2 Hz, 1H),

Ir(III)-Catalyzed C–H Functionalization of Triphenylphosphine Oxide toward 3-Aryl Oxindoles

“…With the rapid development of cross-coupling reactions, the transition-metal-catalyzed α-arylation of oxindoles with aryl halides or esters has become a popular alternative approach (Figure a). Recently, 3-diazooxindole compounds have been applied in various α-arylations through a range of strategies . For example, the Dastidar group reported a Rh­(II)-catalyzed intermolecular C–H insertion of indole with 3-diazooxindole .…”

Recent advances in transition-metal-catalyzed carbene insertion to C–H bonds

“…The readily available Co(II) complex [Co(MeTAA)] (MeTAA = tetramethyltetraaza [14]annulene) proved to be an efficient catalyst enabling intramolecular carbene insertion to alkenyl C-H bond in o-cinnamyl N-tosylhydrazones (366). 364 The reaction proceeded via a Co(III)-carbene radical pathway to afford functionalized 1H-indene derivatives (367). Various functional groups such as ester groups CO 2 Me (86%), CO 2 Et (78%), CO 2 nBu (80%), CO 2 tBu (76%), and CO 2 Ph (82%), amide CONMe 2 (98%), cyano (52%), and phenyl (85%) were introduced onto the vinylic double bond, affording the target products in good to excellent yields (eqn ( 93)).…”

Transition Metal Promoted Cascade Heterocycle Synthesis through C−H Functionalization

“…Given the chemical importance of furans, Lee and co‐workers developed a rhodium‐catalyzed C−H functionalization/annulation protocol for the synthesis of densely functionalized furans 81 exploiting pyrazole as directing group for the reaction . They envisioned that the reaction between cinnamyl‐pyrazoles 80 and diazocompounds 48 would provide the desired product.…”