Metal-free regio- and chemoselective sulfonocyclization of tertiary enamides to access nobenzene-fused medium-sized rings via SO2 insertion

Abstract

Azocines, as privileged motifs, are essential to material science and medicinal chemistry because of their unique 3D spatial properties. However, in contrast to recent developments in the synthesis of benzene-fused azocines, the synthesis of tetrahydroazocines remains challenging and quite limited, as their synthesis process relies mostly on noble transition-metal catalysts. We developed a metal-free and effective route to synthesize tetrahydroazocines containing various sulfonyl groups via the metal-free radical cascade cyclization of 3-aza-1,7-enynes with DABSO and aryl diazonium tetrafluoroborates. This method involved the precise control radical regio-and chemo-addition of sulfonyl to alkynes and sequential 8-endo-trig cyclization with alkenes.