Harnessing Carbene Reactivity of [1.1.1]Propellane for [2,3]-Sigmatropic Rearrangement: Application and Mechanistic Studies

[1.1.1]Propellane is a highly strained smallest tricyclic hydrocarbon, and its reactivity is primarily engrossed by addition reactions across the strained C-C bond, leading to the formation of bicyclo[1.1.1]pentane derivatives. Herein, we present an unprecedented [2,3]-sigmatropic rearrangement that uses [1.1.1]propellane as a carbene precursor to rapidly access allenylated or allylated methylenecyclobutanes. The reaction is highly efficient and scalable, works well under mild conditions, and can tolerate remarkable functional groups on propargyl and allyl sulfides/selenides. Another significant achievement of this approach is the utility of the obtained products in synthesizing substituted bicyclo[2.1.1]hexanes, potential bioisosteres of ortho and meta-substituted benzenes, by developing a novel photocatalyzed radical cascade cyclization. Density functional theory calculations have suggested that the mechanism of this reaction proceeds via a Cu(I)-assisted five-membered envelope transition state to give the [2,3]-rearrangement product.