Selective Synthesis of Multifunctionalized 2,3-Dihydroinden-1-ones and 1,3-Dihydroisobenzofurans from the Reaction of o-Alkynylbenzaldehydes with Imines Steered by N-Heterocyclic Carbene/Copper(II) and N-Heterocyclic Carbene/Base Cascade Catalysis.

We report in this paper the N-heterocyclic carbene/transition metal and N-heterocyclic carbene/base cascade catalysis in the reaction of o-alkynylbenzaldehydes with N-acylimines, demonstrating the example of reaction pathways steered by catalysts. Under the catalysis of a thiazole carbene/Et3N followed by Cu(OAc)2 in acetonitrile at ambient temperature, o-alkynylbenzaldehydes underwent reaction with N-acylimines that were generated in situ from N-((aryl)(tosyl)methyl)amides to produce a pair of Z- and E-2-amido-3-benzylidene-1-indanones in 47-92% total yields. The reaction of the same substrates in the presence of a thiazole carbene and Cs2CO3, on the other hand, afforded (1 E,3 Z)-1-amidobenzylidene-3-benzylidene-1,3-dihydroisobenzofurans in 54-89% yields.