Enantioselective Michael Addition of 4‐Hydroxycoumarins to β,γ‐Unsaturated α‐Oxophosphonates Catalysed by a Bifunctional Squaramide Bearing a Structurally Rigid 9,10‐Ethylene‐9,10‐dihydroanthracene Skeleton

Abstract

A bifunctional squaramide based on (R,R)‐11,12‐diamino‐9,10‐ethylene‐9,10‐dihydroanthracene has been developed, and it has demonstrated great advantages over previously reported organocatalysts in the asymmetric Michael addition of 4‐hydroxycoumarins to β,γ‐unsaturated α‐oxophosphonates. Upon quenching the generated β‐4‐hydroxy‐2‐oxo‐2H‐chromen‐3‐yl‐substituted acylphosphonate intermediates with DBU and an alcohol or amine as a second nucleophile, the corresponding β‐substituted carboxylates or amides were obtained in acceptable to excellent yields and with high levels of enantioselectivity (80–97 % ee) in a one‐pot fashion.

Enantioselective Synthesis of 2,3‐Dihydrofurocoumarins by Squaramide‐Catalyzed Michael Addition/Cyclization of 4‐Hydroxycoumarins with β‐Nitrostyrenes

“…Specifically, unsaturated α‐keto esters are useful acceptors for enantioselective Michael additions of coumarin derivatives . Wang, Zhou, and coworkers showed that structurally rigid squaramides catalyzed Michael addition of 4‐hydroxycoumarin to unsaturated α‐oxo phosphonates . In addition, there are two examples of organocatalytic asymmetric Michael addition of 4‐hydroxycoumarin to nitroalkenes.…”

Stereoselective Synthesis of Highly Functionalized Nitrocyclopropanes through the Organocatalyic Michael‐Addition‐Initiated Cyclization of Bromonitromethane and β,γ‐Unsaturated α‐Ketoesters

“…As revealed in Table 1, thiourea I and II and squaramides III , IV , Va , Vb all efficiently promoted the desired cyclopropanation reactions at 10 mol % catalyst loading in CH 2 Cl 2 , thereby delivering the corresponding nitrocyclopropane ( 3a ) with enantioselectivities from 70 to 87 % (Table 1, entries 1–6). Surprisingly, squaramide catalyst VI , which contained a structurally rigid 9,10‐ethylene‐9,10‐dihydroanthracene skeleton and had previously been found to efficiently catalyze the Michael addition of 4‐hydrxoycoumarins to β,γ‐unsaturated α‐ketophosphonates,17 was inactive for the model reaction and failed to provide the product ( 3a ). Bifunctional squaramide catalyst IV , which was derived from quinine, was the best choice in terms of enantioselectivity (Table 1, entry 4, 87 % ee ).…”

Polymeric p–n Nanojunctions: Formation and Electrochemical Properties of C60‐Pd@Polypyrrole Core–Shell Nanoparticles

“…A closely related asymmetric one‐pot reaction of 4‐hydroxycoumarins 34 with β,γ‐unsaturated α‐oxo phosphonates 149 catalyzed by an amino‐squaramide XXIV based on ( R,R )‐11,12‐diamino‐9,10‐ethylene‐9,10‐dihydroanthracene provided the corresponding β‐substituted esters or amides 165 in low to high yields and with good levels of enantioselectivities (Scheme ) 83…”