Pd-catalysed regioselective C–H functionalisation of 2-pyrones

Abstract

A new synthetic methodology for the catalytic C–H functionalisation of 2-pyrones is described which proceeds regioselectively at the C3 position, mirroring the observed regioselectivity in 6π-electrocyclisation/oxidative aromatisation reactions of related compounds. Insight into the reaction mechanism is provided, with support for a neutral palladium(II) pathway. Cationic palladium(II) complexes possessing 2-pyrones are unstable and readily undergo Pd^II→P transfer at ambient temperature resulting in phosphonium salt formation (and Pd⁰L_n species).