Synthesis Of Alkylboronates Via Iron-catalyzed Boration Of Alkenes

Alkylboronates are among the most versatile C-nucleophiles in organic synthesis.Moreover,pinacol alkylboronates can be stored in air and readily purified as common organic compounds because of their stability in moisture and air.Pinacol alkylboronates can also be readily converted into the corresponding alcohols,aldehydes,amines,etc.Thus,efficient approaches toward the synthesis of diverse alkylboronates have received much attention.Transition-metal catalyzed boration of alkenes is an efficient method for the synthesis of alkylboronates with various functional groups and different structures.In the past decades,Most of the transition-metal catalysts involved precious metals such as Rh,Pt,Pd.With respect to sustainable and green chemistry,iron based catalytic systems have received signigicant growing interests because iron element are earth-abundant,inexpensive and environment-friendly.In this dissertation,three types of alkylboronates with different structure and rich functional groups were synthesized by iron-catalyzed boration of alkenes.(1)The ferrous chloride catalyzed anti-Markovnikov hydroboration of un-activated aryl alkenes with bis(pinacolato)diboron(B2pin2)in the absence of ligands has been reported.The reaction proceeded smoothly in the presence of ferrous chloride,BuOK and rBuOH,and the alkylboronates were obtained in high yield with high regioselectivity for a large range of aryl alkenes with wide functional-group compatibility.(2)The ferrous chloride catalyzed method for the synthesis of gem-difluoroallylboronates via boration/?-fluorine elimination of trifluoromethyl alkenes in the absence of ligands is described.Thus,a full range of gem-difluoroallylboronates were obtained in high yield under mild conditions.As an important fluorinated building block,gem-difluoroallylboronate can be readily converted into gem-difluoroallyl alcohol,difluoromethylboronate and difluorohomoallylic alcohol.Furthermore,2-(2-((3r,5r,7r)-adamantan-1-yl)-3,3-difluoroallyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane(5x)can be used as an intermediate for the synthesis of a GABAB receptor agonist 3-(4-acetylphenyl)-1-((3r,5r,7r)-adamantan-1-yl)-2,2-difluoro-3-hydroxypropan-1-one(10).(3)An efficient approach to cyclopropylboronates via iron-catalyzed boration of allylic esters is described.The reactions of allylic esters and B2pin2 proceed smoothly catalyzed by FeC13/DPPP.Thus,a wide range of cyclopropylboronates with broad functional-group compatibility were obtained.