Study On The Synthesis Of 2-carbonylpyrrole By Rhodium-catalyzed Transannuation Of 1-sulfonyl-1,2,3-triazole With β-diketone

Transition metal-stabilized carbene species,prepared by metal-catalyzed decomposition of diazo compounds,is a class of exceedingly active intermediates and have been widely applied in organic transformations.Transition metal-stabilized carbene species has become an important reactive intermediates for organic synthesis.In 2008,Fokin and Gevorgyan reported that 1-sulfonyl-1,2,3-triazoles could undergo a Dimroth-type equilibrium to generate α-imino diazo isomer.Readily available 1-sulfonyl-1,2,3-triazoles can be prepared by the copper-catalyzed azide-alkyne cycloaddition reaction(CuAAC).Since then,1-sulfonyl-1,2,3-triazoles have been wildly used as precursors of diazo compounds,which can be effectively decomposed to α-imino rhodium carbine by rhodium catalyst.α-Imino rhodium carbene can undergo a series of transformations,including transannulation cyclopropanation,C–H,O-H or N-H insertion.This thesis was mainly focused on formation of 2-carbonylpyrrole by trapping the α-imino carbene with β-diketone.To improve the yield,evaluation of the effects of the reaction parameters was carried out.At last,we confirmed the best condition of the reaction:Under a nitrogen atmosphere,the use of 1.5 mol% of Rh2(piv)4,1.5 equivalents 1-sulfonyl-1,2,3-triazole and β-diketone in 1,2-DCE at 70℃ gave 2-carbonylpyrrole in moderate to excellent yield.Most 1-Sulfonyl-1,2,3-triazole and β-diketone we investigated reacted smoothly to afford 2-carbonylpyrrole compounds in moderate to high yields.The CH3O-,Br-,Cl-,F-group are tolerated in the reaction.Excellent regioselectivity was observed when benzoylacetone derivatives was used.More importantly,carbonyl substituted enol was used for the first time to trap α-imino carbine,offering much more flexibility in pyrrole synthesis.