Palladium-catalyzed aminocarbonylation of 3-iodochromone was studied in the presence
of primary and secondary amines using atmospheric pressure of carbon monoxide as
a carbonyl source. This procedure successfully provided a library of chromone-3-carboxamides
and 3-substituted chroman-2,4-diones in 40 to 92% isolated yields. The reaction proceeded
via highly chemoselective aminocarbonylation (up to 100%) in the presence of secondary
amines by using monodentate or bidentate phosphine ligands. The tendency of 3-iodochromone
substrate to undergo ANRORC rearrangement with N-nucleophiles was crucial to shift
the reaction toward an unprecedented chemoselective carbonylative transformation,
where a late-stage carbonyl insertion is favored concomitantly to the last ring-closure
step. The proposed azaMichael addition/ring-opening/intramolecular aryloxycarbonylation
sequence showed compatibility, uniquely, to primary amines when XantPhos was used
as a ligand. The solid-state structures of chromone-3-carboxamide (2a) and chroman-2,4-dione
(3s) were undoubtedly established by single-crystal XRD analysis. A catalytic cycle
was proposed to rationalize the formation of the two types of carbonylated compounds.
