Condition-ControlledDivergent Access to Spirodihydrofurans,Biscoumarins, Tetraketones, and Bisindenetetraones from Alkyne-TetheredIndenediones

Abstract Unified synthesis of structurally diverse oxygenated polycycles─spirodihydrofurans, biscoumarins, tetraketones, and bisindenetetraones─from readily accessible alkyne-stitched 1H-indene-1,3(2H)-diones has been described. Divergent reaction pathways were achieved from a common starting material through tactical modulation of the reaction conditions. In the presence of a base and a Lewis acid catalyst, the reaction of indenediones with 1,3-diones or their equivalents proceeded through a sequential 1,4-conjugate addition, cyclopropanation, and cyclative ring-expansion cascade to afford spirodihydrofurans with high regioselectivity. In the absence of Lewis acids, reactions with 1,3-diones delivered biscoumarins and tetraketones via a degradative annulation pathway. Notably, in the absence of external nucleophiles, slight modification of the reaction conditions promoted oxidative homodimerization of the indenediones to furnish bisindenetetraones. This condition-controlled strategy exhibited broad substrate scope and enabled high chemoselectivity and regioselectivity control in the construction of complex oxygenated polycyclic architectures.