[2,3]-Sigmatropic rearrangement with [1.1.1]propellane
Suparnak Midya, Aksar Ali, Durga Prasad Hari
Abstract
The most established reactivity of [1.1.1]propellane involves addition reactions at the bridge C-C bond, resulting in the formation of bicyclo[1.1.1]pentane derivatives. Herein, we present a [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 a diverse range of 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 photocatalyzed radical cascade cyclization. Density functional theory calculations suggest the involvement of a copper-bound five-membered transition state. [1.1.1]Propellane is a highly strained smallest tricyclic hydrocarbon, and its reactivity is primarily focused on addition reactions across the strained C-C bond, leading to the formation of bicyclo[1.1.1]pentane derivatives. Herein, the authors present a [2,3]-sigmatropic rearrangement that uses [1.1.1]propellane as a carbene precursor to rapidly access allenylated or allylated methylenecyclobutanes.