Iron-Catalyzed Dearomatization of Biaryl Ynones with Aldehydes via Double C–H Functionalization in Eco-Benign Solvents: Highly Atom-Economical Synthesis of Acylated Spiro[5.5]trienones

The multiple C–H bonds of biaryl ynones render the 6-exo-trig regioselective C–H activation dearomatization to spiro[5.5]trienones challenging since the competing reactions of C–H bonds on Ar1 or the ortho-C–H bonds on Ar3 may result in 5-exo-trig cyclization to indenones or 6-exo-trig ortho-dearomatization, respectively. We here report an unprecendented dearomatization of biaryl ynones with aldehydes via double C–H functionalization where a regiospecific remote unactivated para-C–H functionalization of biaryl ynones efficiently furnishes acylated spiro[5.5]trienones. This cascade cyclization features a green catalyst and solvent and high atom- and step-economy.