A polystyrene-supported 9-amino(9-deoxy)epi quinine derivative for continuous flow asymmetric Michael reactions

Abstract

A polystyrene (PS)-supported 9-amino(9-deoxy)epi quinine derivative catalyzes Michael reactions affording excellent levels of conversion and enantioselectivity using different nucleophiles and structurally diverse enones. The highly recyclable, immobilized catalyst has been used to implement a single-pass, continuous flow process (residence time: 40 min) that can be operated for 21 hours without significant decrease in conversion and with improved enantioselectivity with respect to batch operation. The flow process has also been used for the sequential preparation of a small library of enantioenriched Michael adducts.

Catalytic Enantioselective Flow Processes with Solid‐Supported Chiral Catalysts

“…However, this array of functionalities makes the anchoring of such scaffolds far from straightforward. We decided to use the quinuclidine vinyl group for that purpose, which gave rise to the triazole‐linked resin 14 in four synthetic steps . The reaction of choice this time was the Michael addition of α‐nitroesters to enones, given the already mentioned ketone preference of primary amines.…”

Synthesis of Chiral Polyamides Containing an (R,R)‐1,2‐Diphenylethylenediamine Monosulfonamide Structure and Their Application to Asymmetric Transfer Hydrogenation Catalysis

“…Chiral synthetic polymers have attracted much attention owing to their unique properties, including chiroptical properties, and their applications, including asymmetric catalysis and chiral separation chemistry . In asymmetric catalysis, the immobilization of chiral catalysts onto solids, such as crosslinked polystyrene and silica, is frequently used to prepare recoverable heterogeneous catalysts for asymmetric synthesis. In addition to their easy recoverability and reusability, polymer chains can provide specific chiral catalyst conformations in their microenvironment, which sometimes increases the reactivity and stereoselectivity in asymmetric reactions .…”

An Adverse Effect of Higher Catalyst Loading and Longer Reaction Time on Enantioselectivity in an Organocatalytic Multicomponent Reaction

“…The more favourable increase in entropy could be the driving force for the irreversible racemisation and would reach the completion when thermodynamic equilibrium is achieved ( ee ≈0 %) . This assumption was further revalidated by the reaction of 1 and 6 b in presence of 10 mol % of Q2 and 20 mol % TFA (see Scheme C) . It is interesting to note that the initially formed enatiomerically pure product (+)‐ 4 b (94 % ee ) was susceptible to the erosion of enantiopurity over a period of time (30 h, 72 % ee ).…”