TfOH-catalyzed direct Michael addition and cascade cyclization reactions of unactivated ketones: A divergent route to functionalized benzofurans and benzofuro[3,2-b]pyridines

Abstract

TfOH-catalyzed direct Michael addition and cascade cyclization reactions of azadienes with unactivated ketones have been developed by controlling the amount of TfOH, which provide a divergent approach to 2,3-disubstituted benzofurans and benzofuro[3,2-b]pyridines. Due to their weak nucleophilicity, unactivated ketones are used for the first time to react with azadienes instead of preactivated carbonyl compounds, in which the catalyst acidity is a key parameter. This approach with commercial ketones in mild reaction conditions shows synthetic and environmentally benign advantages including metal-free catalyst, atom economy and simple operation.