Cascade Reaction of Alkynols and 7-Oxabenzonorbornadienes Involving Transient Hemiketal Group Directed C-H Activation and Synergistic RhIII/ScIII Catalysis.

As the first cascade C-H activation directed by a transient group, reaction of alkynols and 7-oxabenzonorbornadienes has been achieved via synergistic rhodium and scandium catalysis to afford spirocyclic dihydrobenzo[a]fluorenefurans. This transformation proceeds by a transient hemiketal group directed C-H activation, dehydrative naphthylation, and intramolecular Prins-type cyclization. Mechanistic studies and density functional theory calculations indicate that the rate-determining step is C-H bond cleavage and both the transient hemiketal group and synergistic RhIII/ScIII catalysis play key roles.