A Tandem Isomerization/Prins Strategy: Iridium(III)/Brønsted Acid Cooperative Catalysis

Abstract

In Gemeinschaftsarbeit: Eine milde und effiziente Isomerisierungs‐Protonierungs‐Sequenz unter kooperativer Katalyse durch kationische Iridium(III)‐Spezies und Bi(OTf)3 ergibt Pyran‐anellierte Indole. Drei verschiedene Cyclisierungsarten führen in guten Ausbeuten zu den entsprechenden Gerüsten von biologisch aktiven Substanzen. In Gegenwart eines chiralen Phosphats sind auch N‐substituierte Indole enantioselektiv zugänglich.

Ruthenium‐Catalyzed Tandem‐Isomerization/Asymmetric Transfer Hydrogenation of Allylic Alcohols

“…Therefore, the search for and optimization of new synthetic pathways, which allow for short reaction routes, is of high importance. It is beneficial if such synthetic procedures contain steps that can be combined in a sequential manner, called tandem or cascade reactions, which makes it possible to use unstable intermediates, produce less waste, use less solvent, and allow for faster formation of the desired product 1. Here, we present a catalytic cascade protocol, which allows for the formation of enantiomerically enriched secondary alcohols by initial isomerization of racemic allylic alcohols, followed by reduction of the resulting ketones.…”

Synthesis of Heterocycles through Transition‐Metal‐Catalyzed Isomerization Reactions

“…Most recently, the groups of Nielsen36 and Scheidt37 independently reported catalyst systems for the generation of oxocarbenium ions, which upon reaction with internal indole nucleophiles afforded tetrahydropyranoindoles. By screening a range of catalysts, Nielsen and co‐workers found the use of [RuClH(CO)(PPh 3 ) 3 ] (5 mol %) and diphenyl phosphate (5 mol %) to be optimal for the synthesis of products 67 , and the products were obtained in good yields, generally >60 % (Scheme , selected examples) 36.…”

“…Scheidt and co‐workers reported a cooperative catalytic system consisting of [IrH 2 (thf) 2 (PPh 2 Me) 2 ]PF 6 (1 mol %) and Bi(OTf) 3 (1 mol %) for the formation of three distinct types of biologically relevant pyran‐fused indole scaffolds, depending on the appendage of the allyl group (Scheme ) 37. Products of the types 73 and 77 were isolated in good to excellent yields (65–92 %), whereas type 75 products generally were obtained in lower yields (52–70 %).…”

Gold‐Catalyzed Dual Annulation of Homopropargyl Alcohols with Nitrones: Synthesis of Tetrahydropyrano[4,3‐b]indole Scaffolds

“…[19] Furthermore, the tetrahydropyrano [4,3-b]indoles are privileged heterocyclic motifs that frequently occur in a plethora of bioactive molecules, such as anti-inflammatory and anti-tumor compounds. [20]…”