Lewis Acid Regulated Divergent Catalytic Reaction between Quinone Imine Ketals (QIKs) and 1,3‐Dicarbonyl Compounds: Switchable Access to Multiple Products Including 2‐Aryl‐1,3‐Dicarbonyl Compounds, Indoles, and Benzofurans

Abstract

A catalytic Lewis acid regulated reaction between quinone imine ketals (QIKs) and 1,3-dicarbonyl compounds provides a divergent and tunable approach to a variety of skeletons, including a series of 2-aryl-1,3-dicarbonyl compounds, indoles, and benzofurans. The use of lithium chloride and ferrous bromide gives C3-or C2-alkylation products of the QIKs. The combination of ferrous bromide and trifluoromethanesulfonic acid delivers indole derivatives. Sequential hydrolysis and C3-alkylation occur in the presence of ytterbium (III) trifluoromethanesulfonate and stoichiometric amounts of water. When the reaction is performed with trifluoromethanesulfonic acid and stoichiometric amounts of water, benzofuran is obtained. This protocol utilizes mild conditions, exhibits regio-and chemoselectivity, and has broad functional group tolerance.

A Comprehensive Review on Benzofuran Synthesis Featuring Innovative and Catalytic Strategies

“…For the construction of carbon–carbon bonds, Bronsted-acid-mediated reactions have gained substantial significance in organic synthesis. 97 Taking into account the efficiency of Bronsted-acid-catalyzed reactions, Chen et al 98 in 2022 proposed the triflic-acid-mediated reaction of substituted quinone imine ketals (QIK) 86 with substituted dicarbonyl compounds 85 involving water and HFIP (hexafluoroisopropanaol) medium to achieve substituted benzofuran cores 87 in high yields ( Scheme 25 ).…”