Chiral Brønsted Acid from Chiral Phosphoric Acid Boron Complex and Water: Asymmetric Reduction of Indoles. (9th January 2020)

• Record Type: Journal Article
• Authors: Yang, Kai; Lou, Yixian; Wang, Chenglan; Qi, Liang‐Wen; Fang, Tongchang; Zhang, Feng; Xu, Hetao; Zhou, Lu; Li, Wangyang; Zhang, Guan; Yu, Peiyuan; Song, Qiuling
• Is Part Of: Angewandte Chemie. Volume 132:Number 8(2020)
• Page Start: 3320
• Page End: 3325
• Publication Date: 2020-01-09
• Subjects: Asymmetrische Katalyse -- Bor -- Brønsted-Säure -- Heterocyclen -- Wasser; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201913656
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: A new chiral Brønsted acid, generated in situ from a chiral phosphoric acid boron (CPAB) complex and water, was successfully applied to asymmetric indole reduction. This "designer acid catalyst", which is more acidic than TsOH as suggested by DFT calculations, allows the unprecedented direct asymmetric reduction of C2‐aryl‐substituted N‐unprotected indoles and features good to excellent enantioselectivities with broad functional group tolerance. DFT calculations and mechanistic experiments indicates that this reaction undergoes C3‐protonation and hydride‐transfer processes. Besides, bulky C2‐alkyl‐substituted N‐unprotected indoles are also suitable for this system. Abstract : Es ist komplex : Eine neue chirale Brønsted‐Säure, die in situ aus einem chiralen Phosphorsäure‐Bor(CPAB)‐Komplex und Wasser erzeugt wird, ermöglicht die direkte asymmetrische Reduktion von C2‐Aryl‐substituierten N‐ungeschützten Indolen. Die Reaktion zeichnet sich durch gute bis exzellente Enantioselektivitäten mit breiter Verträglichkeit funktioneller Gruppen aus.