Access to Oxoquinoline Heterocycles by N‐Heterocyclic Carbene Catalyzed Ester Activation for Selective Reaction with an Enone

Abstract

Organocatalytic ester activation is developed for a highly selective cascade reaction between saturated esters and amino enones. The reaction involves activation of the b-carbon atom of the ester as a key step. This method allows a single-step access to multicyclic oxoquinoline-type heterocycles with high enantiomeric ratios. Angewandte Chemie 6625

Alkynyl Acylazolium: A Versatile 1,3‐Bielectrophilic 3C‐Synthon in NHC‐Organocatalysis

“…Esters are a basic class of important carbonyl compounds that play a significant role in organic synthesis. Particularly, in the field of NHC‐catalysis, the activation of p ‐nitrophenyl esters to give the acylazolium intermediates has been well established considering the good leaving ability of the p ‐nitrophenoxide in the starting esters [17–21] . Taking this advantage into consideration, in 2017, Chi's [22] and Du's [23] group almost simultaneously developed two different NHC‐catalyzed annulation reactions for constructing heterocyclic skeletons using alkynoic p ‐nitrophenyl esters as the precursors of alkynyl acylazoliums, respectively.…”

Exploring Molecular Complexity by N‐Heterocyclic Carbene Organocatalysis: New Activation and Reaction Diversity

“…On the other side, lactam 18 a and lactone 20 a products were obtained through [3 + 2] cycloaddition reactions between the saturated carboxylic ester 13 and corresponding imine 17 and activated ketone 19 (Scheme 6). [15] Propionic acid scaffold bearing a stereogenic α-carbon is widely present in bioactive molecules and non-steroidal antiinflammatory drugs such as ibuprofen and ketoprofen. The carboxylic esters activation approach for stereoselective synthesis provides an excellent platform to prepare this type of functional molecules.…”

“…On the other side, lactam 18 a and lactone 20 a products were obtained through [3+2] cycloaddition reactions between the saturated carboxylic ester 13 and corresponding imine 17 and activated ketone 19 (Scheme 6). [15] …”

Synthesis of 3,4‐Fused 2‐Quinolones from an (ortho‐Aminophenyl)propiolate via Sequential Cycloaddition/Lactam Formation

“…[1,2] Therefore, the development of a novel method to efficiently construct this valuable N-heteropolycyclic motif is exceedingly important for drug discovery. In this regard, the sequential cycloaddition/lactam formation of (ortho-aminophenyl)propiolates constitutes a straightforward strategy for the diversity-oriented synthesis of 3,4-fused 2-quinolones because various types of cycloaddition reactions are applicable (Scheme 1).…”