Palladium-catalyzed B-H Bond Activation Of O-carboranes To Construct B-O And B-B Bonds

o-Carboranes,a kind of boron cluster compounds of three elements,carbon,boron and hydrogen,has been widely used in the field of medicine and engineering.For example,carborane derivatives have been used in propellants due to their good combustion performance and adding them into anti-tank high-burning rate propellants can effectively improve their burning rate.In medicine,It has been used as boron neutron capture therapy,this radiation method is one of the ways to achieve effective precision therapy in cancer treatment.Therefore,the synthesis of o-carboranes derivatives is very important in the study of carboranes.In the past decade,the efficiency and scope of directed equivalent B（4,5）–H and B（3,6）–H functionalization reactions have been substantially improved via substrate or catalyst strategy.In sharp contrast,directed inequivalent B（3,4）–H functionalization reactions are rare.Therefore,this paper has studied the research on the"Palladium-catalyzed B-H bond activation of o-carboranes to construct B-O and B-B bonds".A new way for regioselective B（3,4）–H activation of o-carborane via a ligand has been reported.First,a pyridine group has been introduced on the cage carbon,and then B（3）-monoacyloxylated and B（3,4）-diacyloxylated o-carboranes were achieved by adding amino acids and phosphoric acid ligands using carboxylic acid as source of acyl groups.Through experimental exploration,we found that fatty acids,aromatic acids,cinnamic acids and some complex drug molecules carboxylic acids can react.The aromatic acid benzene ring with electron-absorbing and electron-donating groups and heterocyclic ring can react,and has a high yield.The products were separated by column chromatography for NMR spectra(¹H,¹³C,¹¹B,¹¹B{¹H}and ¹⁹F),high resolution mass spectra,Theoretical calculations,kinetic experiments,single-crystal X-ray diffraction and melting point test.Dehydrogenation coupling has been a direct and effective method in the history of o-carboranes,but the dehydrogenation coupling of B（3,6）-H still presents significant challenges.The o-carborane B（3,6）-H is self-conjugated selectively and can react at room temperature.The products were separated by column chromatography for NMR spectra(¹H,¹³C,¹¹B,¹¹B{¹H}and ¹⁹F),high resolution mass spectra,single-crystal X-ray diffraction and melting point test.