Palladium‐Catalyzed 6‐endo‐Selective Oxycyclization–Alkene Addition Cascades of ortho‐Alkynylarylcarboxamides and α,β‐Unsaturated Carbonyl Compounds

Regio- and chemoselective palladium-catalyzed cyclization–coupling cascade reactions between ortho-alkynylarylcarboxamides and methyl vinyl ketone or acrylaldehyde are described. An initial 6-endo-oxypalladation of the triple bond is followed by a C–C coupling to give structurally diverse isochromenimines (and related heterosubstituted derivatives), in which the α,β-unsaturated carbonyl moiety is incorporated as an alkyl-type exocyclic side chain. The coupling products were obtained in 76–97 % yield (average 86 % yield) without significant interference from Heck or alternative regiochemical pathways. In contrast to related cases, these cascade reactions do not require the use of protic solvents and excess amounts of halide additives, and they proceed effectively under either PdCl2 catalysis in the presence of substoichiometric amounts of added KI or PdI2 catalysis without any additive.