Heterocyclic Derivative Syntheses by Palladium-Catalyzed Oxidative Cyclization−Alkoxycarbonylation of Substituted γ-Oxoalkynes

4-Yn-1-ones containing different substituents, prop-2-ynyl α-ketoesters, and prop-2-ynyl α-ketoamides have been caused to react catalytically under oxidative carbonylation conditions to give
tetrahydrofuran, dioxolane and oxazoline, dihydropyridinone, and tetrahydropyridinedione derivatives in satisfactory yields. Reactions were carried out in MeOH or MeCN/MeOH mixtures at 65−100 °C in the presence of catalytic amounts of PdI2 in conjunction with KI under 32 bar (at 25 °C)
of a 3:1 mixture of CO and air. Anti and syn 5-exo-dig cyclization modes account for the formation
of different products. It has been found that cyclopentenone, dihydropyridinone, and tetrahydropyridinedione derivatives, formed when the reaction is carried out at higher temperature and for
a longer time, can also be selectively obtained through an acid treatment of tetrahydrofuran and
oxazoline derivatives involving an unusual rearrangement. The structures of 6-methoxy-2,2-dimethyl-3-oxo-5-phenyl-2,3-dihydropyridine-4-carboxylic acid methyl ester and 2,2,5-trimethyl-3,6-dioxo-1,2,3,6-tetrahydropyridine-4-carboxylic acid methyl ester have been confirmed by X-ray
diffraction analysis.