N‐Heterocyclic Carbene‐Catalyzed Double Michael Addition: Stereoselective Synthesis of Spirofluorenes and Multisubstituted Indanes

Abstract

The strong Brønsted basic character of N‐heterocyclic carbenes (NHCs) has been used to promote the cascade double Michael addition between fluorenes and dienones. Under catalyst loadings of 1–5 mol% of NHC, fluorene reacts with divinyl ketones (DVKs) to afford anti‐spirofluorene compounds in high yields. However, when benzenedi(enones) were employed as Michael acceptors in the presence of 10 mol% of NHC, fluorene undergoes a different inter‐ and intramolecular cascade double Michael addition, providing multi‐substituted indanes in high yields with excellent diastereoselectivity.magnified image

SuFEx Reactions of Sulfonyl Fluorides, Fluorosulfates, and Sulfamoyl Fluorides Catalyzed by N-Heterocyclic Carbenes

“…Based on the previous studies of the Broønsted basicity of NHCs, a plausible mechanism for the reaction was proposed and depicted in Scheme . NHC acts as a carbon-centered Broønsted base to attack the acidic proton of alcohols through hydrogen bonding to form an oxy anion/azolium ion complex I , which might trigger the following SuFEx reaction with sulfonyl fluoride to give sulfonate ester with the release of free carbene.…”

“…In sharp contrast, reactions based on the Broønsted basic properties of NHCs have been far less examined. To date, only several very limited reactions, such as NHC-catalyzed transesterifications and Michael additions, had been reported. In these reactions, NHCs acted as a strong Broønsted base to activate proton-containing nucleophiles through the formation of hydrogen bonding.…”

Unprecedented Multicomponent Organocatalytic Synthesis of Propargylic Esters via CO2 Activation

“…Recently-reported transformations, catalyzed by NHCs, deal with the utilization of nitroalkenes to prepare three-to five-carbonatom building blocks, 12 the synthesis of 4difluoromethylquinolines, 13 polymerization reactions, 14 1,6conjugate addition reactions, 15 Michael additions, 16 and various enantioselective functionalizations. 17 On a different note, propargylic esters can be prepared via several synthetic pathways.…”

Regioselective mono-aza-Michael additions of divinyl ketones with 3-(arylimino)indolin-2-ones: Synthesis of N-enone-functionalized 3-(arylimino)indolin-2-ones

“…1,4-dien-3-ones) have been used as Michael acceptors in recent years to synthesize spiro-, cyano-, and other important compounds. [11][12][13][14][15][16][17][18][19] However, divinyl ketones as Michael acceptors have problems of regioselective control and can undergo 1,2-addition and two kinds of 1,4-addition reactions.…”