Studies On The Reactions Of Rh(Ⅱ)-azavinyl Carbene With 1,3,5-Triazinanes And Mechanistic Insights Into α-Oxo Gold Carbene Activated Sp~3 C-H Insertion

Transition metal carbene species play an important role in organic synthesis due to the versatile reactivities,attractive transformations and easy access.Diazo compounds are traditionally used for the generation of the carbene species through elimination of nitrogen gas.However,diazo compounds are usually unstable,explosive and toxic,which limits their applications in organic syntheses.Therefore,safe surrogates and identifying sustainable for the generation of metal carbenes species have attracted great attention.Alternative carbene precursors have been found,such as hydrazones,cyclopropenes,enynyl ketones,propargylic esters,1,3,5-cycloheptatrienes,alkynes and 1,2,3-triazoles.The related research on alkyne carbene precursor and 1,2,3-triazole carbene precursor was carried out.The reaction of Rh(II)-azavinyl carbene intermediate with 1,3,5-triazinanes was comprehensively studied through both experiments and density functional theory(DFT)calculations.Experimental studies showed that octahydro-1H-purine derivatives could be produced by N-sulfonyl-1,2,3-triazoles with 1,3,5-triazinanes under rhodium catalyst reaction conditions.Afterwards,the template reaction conditions were optimized,which were found to be:N-sulfonyl-1,2,3-triazole(1.2 equiv),1,3,5-triazinanes(1 equiv),Rh2(Oct)4(5 mol%),NaHC03(2 equiv)and cyclohexane as a solvent,the reaction was carried out at 85℃ for 5 hours.Good reaction yields can be obtained under optimal reaction conditions.Subsequently,substrate scope studies showed that the reaction has good versatility for N-sulfonyl-1,2,3-triazoles and 1,3,5-triazinanes.The mechanism of the reaction was further studied by control experiments and DFT calculations.Studies suggested that the 1,3,5-triazinanes might undergo a formal[6+3]cycloaddition with the Rh(Ⅱ)-azavinyl carbene intermediates,which are generated from Rh(Ⅱ)-catalyzed denitrogenation of N-sulfonyl-1,2,3-triazoles.Afterwards,ring-closure of the formed nine-membered ring intermediate via intramolecular nucleophilic addition followed by subsequent rearrangements could afford the final octahydro-1H-purine derivatives.The mechanism of α-oxo gold carbene activated sp3 C-H insertion was studied by DFT calculations.The coordination of gold catalyst to the alkyne moiety of alkynone commenced the reaction mechanism.DFT results revealed that after the nucleophilic addition of 8-methylquinoline N-oxide(an oxidant)and subsequent release of quinoline,the cricital α-oxo gold carbene intermediate counld be formed.The gold carbenoid complex,which is thermodynamically stable,is proposed as the key intermediate for the reaction.The cyclopentanone derivatives can be produced through a sp3 C-H insertion at γ-position by the α-oxo gold carbene.The factors accounting for the regioselectivities of the reaction are steric effect and the stability of the products.