N‐Heterocyclic Carbene‐Catalyzed Enantioselective Intramolecular Annulations to Construct Benzo‐Fused Pyranones with Quaternary Stereocenter

Abstract

A highly enantioselective intramolecular NHC‐catalyzed approach for the synthesis of benzo‐fused pyranones bearing quaternary stereocenter is described. The developed methodology is based on annulation reaction between acyl anion intermediates and β,β‐disubstituted Michael acceptors. The reaction offers streamlined and effective access to target products in a highly stereoselective manner.

Solvent‐Free Synthesis of Quaternary Oxazolidine‐2‐thione β3‐Amino Ester Analogs

“…Flash chromatography was performed using columns of 230–400 mesh silica gel 60 (0.040–0.063 mm). α, β‐Unsaturated hydroxy esters 1 a , [19] 1 b , [20] 1 c , [21] 1 d , [22] 1 e , [23] 1 f , [24] 1 g , [25] and 1 h [26] were prepared according to literature procedures. The spectroscopic data were in agreement with those present in literature.…”

Remote electronic effect on the N-heterocyclic carbene-catalyzed asymmetric intramolecular Stetter reaction and structural revision of products

“…Next, we investigated the reaction of b-disubstituted alkenoate 2b (Table 2) because the absence of an a-proton in the product excludes the possibility of decreasing the enantiomeric excess by the a-deprotonation. [31][32][33][34] The reaction of 2b was much slower than that of 2a and therefore was performed at 40 1C using 20 mol% catalysts. The reaction rate increased as the electronwithdrawing ability of the NHC substituent increased, giving 3b in 44%, 52%, 70%, and 77% yield when the substituent X was Me, H, Br, and NO 2 , respectively (entries 1-4).…”

Synthesis of Novel 1,4-Diketone Derivatives and Their Further Cyclization

“…Cyanide ion, , thiazolium salt, , bis­(amino)­cyclopropenylidenes, chiral bicyclic thiazolium salt, ThDP-linked enzymes like lyases, MenD, and PigD, , and NHCs ,,,− have been utilized as catalysts in the Stetter reaction. The first isolation of free carbenes was carried out independently by Bertrand et al and Arduengo et al, and this discovery led to the emergence of suitable approaches for obtaining medically and biologically important compounds. , Recently, NHCs have performed effective reactions with homoenolates, enolates, vinyl enolates, acyl azoles, and acyl anion reagents to provide products that are not readily available by other means, and their interest in the field of catalytic synthesis is increasing .…”