| Research Abstract |
1.Nucleophilic Borylation Reactions of Vinylic Electrophrles by Tramsition Metal Catalysts/Diboron System
Nucleophilic borylation reactions of vinylic halides or triflates with bis(pinacolato)diboron regiospesifically and stereospecifically or stereoselectrvely proceeded to afford vinylic boron compounds in excellent yields when using a combination of PdCl_2(PPh_3)_2-2PPh_3/KOPh/toluene at 50℃ or that of PdCl_2(PPh_3)_2-2PPh_3/K_2CO_3/dioxane at 80℃. The reactions tolerated various functionalities such as carbonyl and cyano groups. A catalytic cycle may involve oxidative addition of the vinylic electrophiles to a palladium(O) complex, transmetalation between the diboron and a palladium(II) intermediate, and reductive elimination of vinylic boron compound. Sequential reactions, involving necleophilic borylation of vinylic electrophiles with diboron and coupling with distinct vinylic etectrophiles, provided a one-pot procedure for the synthesis of various unsymmetrical conjugated dienes.
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Rhodium-catalyzed 1,4-addition of β-boryl-α,β-unsaturated carbonyl compounds toα,β-unsaturated ketones afforded the corresponding ω-oxo-α,β-unsaturated carbonyl compounds in high yields.
2.Direct Borylation Reactions of Alkenes by Tramsition Metal Catalysts/Diboron System
A Direct borylation reaction of cyclohexene with bis(pinacolato)diboron proceeded via vinylic carbon-hydrogen bond activation to give 1-boryl-1-cyclohexene in a moderate yield when using a combination of 1/2[Ir(OMe)(COD)]_2-(4,4'-di-tert-buty1-2,2'-bipyridine)/hexane at 50℃. The reaction was accompanied by several by-products such as regioisomers and bis(boryl)cyclohexanes. The reaction may proceed through an tris(boryl)iridium(III) intermediate generated by a reaction of the iridium(I) complex with the diboron. Either oxidative addition of the vinylic carbon-hydogen bond to the tris(boryl)iridium(III) complex followed by reductive elimination or insertion of the tris(boryl)iridium(III) complex to a carbon-carbon double bond followed by β-hydride elimination may be operative in catalytic cycles. Less
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