Theoretical Investigation on Brønsted-Base-Catalyzed Diversified Annulations of Ethylidene 1,3-Indenedione and Vinyl 1,2-Diketone Delivering Oxabicyclo[3.2.1] Octane, Spiro[4.5]Decane, and Branched Triquinane

Our DFT calculations provide the first theoretical investigation on Brnsted-base-catalyzed annulation of ethylidene 1,3-indenedione with vinyl 1,2-diketone.After Michael addition between deprotonated ethylidene 1,3-indenedione and vinyl 1,2-diketone, three paths are possible.In path A, intramolecular oxa-Michael addition and proton transfer happen at first followed by intramolecular aldol reaction furnishing oxabicyclo [3.2.1] octane after protonation.In path B, the oxygen heterocyclic rings of deprotonated oxabicyclo [3.2.1] octane are destructed simultaneously through primary complicated ring opening.The ring expansion proceeds via intramolecular aldol reaction followed by readily proton transfer.The intramolecular annulation splits eight membered ring into two five membered ones for branched triquinane.In path C, after proton transfer, intramolecular aldol reaction provides hexacyclic alkene for spiro [4.5] decane.The positive solvation effect is suggested by decreased absolute and activation energies in solution compared with in gas.These results are supported by Multiwfn analysis on FMO composition of specific TSs, and MBO value of vital bonding, breaking.