Chemoenzymatic and enantioselective assembly of the (1α,3aβ,6α,7aβ)-octahydro-1,6-methano-1H-indene framework associated with 2-isocyanoallopupukeanane: validation of a new synthetic strategy and the identification of enantiomeric switching regimes

The octahydro-1,6-methano-1H-indene framework associated with the marine sesquiterpenoid 2-isocyanoallopupukeanane (1) has been prepared in enantiomerically pure form from the cis-1,2-dihydrocatechol 8 using Diels–Alder cycloaddition, oxa-di-π-methane rearrangement and intramolecular enolate alkylation steps as the key bond-forming events. Three distinct strategies for employing such sequences in the selective synthesis of either enantiomeric form of the target framework have been identified.