Development of Allylic Boron Reagents

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1. Nucleophilic Borylation Reactions of Allylic Electrophiles with Diborons(1) Nucleophilic borylation reactions of allylic acetates or halides with bis(pinacolato)diboron regio-and stereoselectively proceeded at 50 degree when using a combination of Pd(dba)2/DMSO or Pd(dba)2-2AsPh3/KOAc/toluene to afford allylic boron compounds in excellent yields. The reactions also tolerated various functionalities such as carbonyl groups. A catalytic cycle may involve oxidative addition of the allylic electrophile to a palladium(0) complex, transmetalation between the diboron and a palladium(II) intermediate, and reductive elimination of the allylic boron compound.(2) Three-component reactions of bis(pinacolato)diboron, allylic acetates, and aldehydes smoothly occurred under the conditions optimized above (Pd(dba)2/DMSO/50 degree), resulting in high yields of acyclic homoallylic alcohols. Sequential reactions, involving nucleophilic borylation of allylic acetates substituted by a carbonyl group in the presence of a Pd(dba)2-2AsPh3 catalyst in toluene at 50 degree and intramolecular allylboration at 100 degree provided cyclic homoallylic alcohols in high yields with high cis-stereoselectivity.2. Synthesis of Allylic Boron Compounds via Transition Metal-Catalyzed Isomerization Reactions of 3-Alkoxyvinylboranes(1) Isomerization reactions of 3-alkoxyvinylboranes stereoselectively proceeded in the presence of [Ir(COD)(PPh2Me)2]PF6 and NiC12(PPh2Me)2 catalyst to give E- and Z-allylic boron compounds, respectively.(2) 3-Alkoxyvinylboranes having a carbonyl functionality underwent the catalytic isomerization followed by intramolecular allylboration to give cyclic ethers in good yields.