Optimised procedures for the one-pot selective syntheses of indoxyls and 4-quinolones by a carbonylative Sonogashira/cyclisation sequence

A selective one-pot synthesis of carbonyl-containing N-heterocyclic compounds has been developed using a carbonylative Sonogashira/cyclisation sequence. Various catalytic protocols were studied (CO pressure, temperature, catalyst identity, base and substrate/catalyst ratio) with the objective of obtaining selectively either indoxyl or 4-quinolone products. The origin of the selectivity toward the 5- or 6-membered ring compounds was explained through the respective role of the various catalytic species involved, whether they are organic or metallic. The non-cyclic common intermediate was selectively prepared using [PdCl₂(dppp)] as catalyst. By using a two-step multi-catalysis, i.e. {[Pd]+HNEt₂}, 4-quinolones were obtained whereas with a tandem catalysis, i.e. {[Pd]/PR₃}, indoxyls were synthesised.