Spiro-Annulation of Ene-diones with Iodonium Ylides: An Anomalous Cloke–Wilson Rearrangement for the Regioselective Synthesis of Spirodihydrobenzofurans

An efficient synthesis of spirodihydrobenzofuran derivatives via the 1,4-conjugate addition of iodonium ylides to indene-1,3(2<i>H</i>)-diones, followed by an anomalous Cloke-Wilson rearrangement is reported. This strategy demonstrates a broad substrate scope with a high degree of regioselectivity control. Computational studies involving the natural orbital bond analysis were explored to explain this anomalous formation of unconventional products. In case of alkyne-tethered indenediones, the same regioselectivity control was observed, but in the presence of scandium-triflate in dimethoxyethane (DME), the normal Cloke-Wilson product was observed as an exclusive product.