Synthesis of 2,5-Dithia-bicyclo[4.1.1]octanes by Silver-Catalyzed Formal (4+3) Cycloadditions of Bicyclobutanes with Benzodithioloimines

Cycloadditions of bicyclobutanes with two- or three-atom reaction partners have been widely exploited to access bicyclo[2.1.1]hexanes and bicyclo[3.1.1]heptanes. However, their application to the synthesis of bicyclo[4.1.1]octane derivatives has remained elusive. Herein, we report silver-catalyzed formal (4+3) cycloadditions between simple bicyclobutanes and benzodithioloimines, establishing a new method for synthesizing previously inaccessible 2,5-dithia-bicyclo[4.1.1]octanes, which have two sulfur atoms in their bicyclo[4.1.1]octane frameworks. This mild method tolerates bicyclobutane substrates with a wide range of substituents. The synthetic utility of this method was demonstrated via various synthetic transformations of the products to yield valuable sulfur-containing bridged bicyclic scaffolds.