B(C₆F₅)₃-Catalyzed Formal (<i>n</i> + 3) (<i>n</i> = 5 and 6) Cycloaddition of Bicyclo[1.1.0]butanes to Medium Bicyclo[<i>n</i>.1.1]alkanes

Abstract

Herein, a B(C₆F₅)₃-catalyzed formal (<i>n</i> + 3) (<i>n</i> = 5 and 6) cycloaddition of bicyclo[1.1.0]butanes (BCBs) with imidazolidines/hexahydropyrimidines is described. The reaction provides a modular, atom-economical, and efficient strategy to two libraries of synthetically challenging medium-bridged rings, 2,5-diazabicyclo[5.1.1]nonanes and 2,6-diazabicyclo[6.1.1]decanes, in moderate to excellent yields. This reaction also features simple operation, mild reaction conditions, and broad substrate scope. A scale-up experiment and various synthetic transformations of products further highlight the synthetic utility.