Asymmetric Synthesis of Spiropyrazolones by Rhodium‐Catalyzed C(sp2)−H Functionalization/Annulation Reactions

• Published in: Angewandte Chemie International Edition Vol. 56; no. 16; pp. 4540 - 4544
• Main Authors: Zheng, Jun, Wang, Shao‐Bo, Zheng, Chao, You, Shu‐Li
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 10.04.2017; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alkynes; Aromatic compounds; asymmetric catalysis; Asymmetric synthesis; C-H functionalization; Catalysts; Chemical reactions; Chemical synthesis; Chemistry; Chemistry, Multidisciplinary; Organic chemistry; Physical Sciences; Pyrazolones; Rhodium; Science & Technology; Substrates; ACTIVATION; HYDROGENATION; alkynes; BIARYL COMPOUNDS; OXIDATIVE ANNULATION; asymmetric catalysis; INTERNAL ALKYNES; C-H functionalization; CHIRAL CYCLOPENTADIENYL LIGANDS; PHOSPHORUS LIGANDS; ALKENES; pyrazolones; RH; rhodium
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201700021

Rhodium‐catalyzed C(sp2)−H functionalization reactions of 4‐aryl‐5‐pyrazolones followed by [3+2] annulation reactions with alkynes provide rapid access to highly enantioenriched five‐membered‐ring 4‐spiro‐5‐pyrazolones. The use of a chiral SCpRh catalyst enabled the synthesis of a large range of spiropyrazolones with all‐carbon quaternary stereogenic centers in up to 99 % yield and 98 % ee from readily available substrates. Enantioenriched five‐membered‐ring 4‐spiro‐5‐pyrazolones were synthesized by the rhodium‐catalyzed C(sp2)−H functionalization of 4‐aryl‐5‐pyrazolones followed by a [3+2] annulation reaction with alkynes. The use of a chiral SCpRh catalyst (see scheme) led to excellent enantioselectivity, reactivity, and regioselectivity in this cascade process.