Gold(I)-Catalyzed and Nucleophile-Guided Ligand-Directed Divergent Synthesis

Transition metal catalysts can mediate a plethora of skeleton rearrangements of a range of substrates to construct complex small molecules. Yet, their potential to transform common substrates into distinct molecular scaffolds has not been fully explored to deliver biologically relevant small molecules. Gold(I)-catalyzed transformations of enynes are amongst the most intriguing rearrangements and provide opportunities to access a range of diverse scaffolds efficiently. In ligand-directed divergent synthesis (LDS), variation of ligands in metal complexes determines the fate of substrates during their transformation into distinct scaffolds. For instance, variation of ligands for the gold(I) catalysts helps to transform oxindole derived 1,6-enynes into several distinct molecular frameworks. In this report, we present how ligand variation in gold(I) catalysts, nucleophile-additives and alkyl and alkynyl substitutions on the 1,6-enynes as well as replacement of the oxindole ring with a different privileged ring-system (PRS) influence the LDS approach to access a wider chemical space. Based on the experimental results, we propose several mechanistic pathways in gold(I)-catalyzed cycloisomerizations and cascade reactions of 1,6-enyne substrates leading to structurally distinct chemotypes.