Access to Spiro-bicyclo[2.1.1]hexanes via BF3∙Et2O-Catalyzed Formal [2π + 2σ] Cycloaddition of Bicyclo[1.1.0]butanes with Benzofuran-derived Oxa(aza)dienes

Herein, we have developed a method for the construction of spiro[benzofuran-2,2'-bicyclo[2.1.1]hexanes] via BF3·Et2O-catalyzed formal [2π + 2σ] cycloaddition of bicyclo[1.1.0]butanes with benzofuran-derived oxa(aza)dienes. This transformation allowed for facile access to a variety of functionalized spiro-bicyclo[2.1.1]hexanes in good yields (up to 99% yield) with excellent regioselectivities and a broad substrate scope (34 examples) under mild reaction conditions. Moreover, the synthetic utility of the cycloadducts were further emphasized through a scale-up experiment and subsequent synthetic transformations.