The Study Of Radical Reactions Mediated By Tri-n-butyl Germanium Hydrogen

Spirocyclohexadienones are common core structures in natural products,pharmaceutical products and functional materials,which are also important intermediates in organic synthesis,can be further synthesized through reduction or other derivative reactions to a variety of saturated spirocompounds with quaternary carbon centers.The development of simple and efficient method for the synthesis of spirocyclohexadienones has attracted wide attention.Traditional approaches on the synthesis of spirocyclohexadienones are mainly focus on transition-metals catalyze,visible light induced,peroxide mediated and so on.Silicon-hydrogen and tin-hydrogen have related works as well,while the dearomatization of aromatic ring requires an oxygen-containing group or N3 in the para position,which can effectively stabilize the cyclohexadienyl radical and obtain the corresponding cyclohexadienone by leaving the protecting group.However,the study of germanium-hydrogen has not been reported yet.This article describes the radical spirocyclization reaction mediated by tri-n-butyl germanium hydrogen.Based on the study of organogermanium chemistry,we used tri-n-butyl germanium hydrogen instead of silicon hydrogen and tin hydrogen,successfully prepared spirocyclohexadienone oxindoles directly from substrates with no substituents at the para position of the aromatic ring with medium yield and good compatibility.We believe that tri-n-butyl germanium hydrogen may have some special effects in free radical reactions and suspected whether it can catalyze the activated esters decarboxylation to form C-N bond.We have developed an efficient and mild method to prepare carbamoyl azides from NHP(N-Hydroxyphthalimide)esters and TMSN3,and found the reaction did not need the participation of germanium hydrogen.The reaction enables primary,secondary,tertiary and aryl carboxylic acid derivatives to be converted to amine derivatives.Mechanistic studies reveal that Curtius rearrangement was responsible for the generation of carbamoyl azides.