Study On The Highly Efficient Conversion Of α-Diazoacetates

As one kind of the most important intermediates in organic syntheses,diazo compounds have been considered to be multifunctional reagents.However,compared with other diazo compounds,β-alkyl substitutedα-diazoacetates have much more reactive sites.This paper mainly focuses on the two highly catalytic reactions ofα-diazoacetates.（1）Metal-free Lewis Acid TrBF₄-catalyzed 1,2-hydride migration ofα-diazoacetates has been developed,affording（Z）-α-β-unsaturated esters in good yields and with high regioselectivities.And the reaction of the gram scale also worked well in87%yield and excellent Z-selectivity with up to Z:E=96:4.On the basis of mechanism experiments,it was found that the harnessing of ion-pair for stereoselectivity control.In addition,TrBF₄ efficiently catalyzed Roskamp reaction ofα-diazoacetates with aldehydes,giving diverseα-branched-β-ketocarbonyls.（2）Visible-light promoted[2+1]and[2+2]cycloaddition reactions ofα-diazoacetates with olefins have been also developed.Under blue LEDs irradiation,Ir（ppy）₃ could catalyzed[2+1]cyclopropanation ofα-diazoacetates and olefins,affording functionalized various cyclopropanes with up to 97%yield.Moreover,It was found that Rh₂（OAc）₄ and Ir（ppy）₃ could synergistically catalyze the[2+2]cycloaddition ofα-diazoacetates and olefins,obtaining excellent yield with up to 84%and high regioselectivity with up to 10:1 d.r..In addition,estrone-and vitamin E-derived cyclobutanes were also obtained in good yields.A number of experimental observations revealed that the[2+1]and[2+2]cycloaddition were achieved through energy transfer and single electron transfer,respectively.