Development of Allylic Boron Reagents

(1)烯丙基乙酸酯或卤化物与双(频那多)二硼的亲核硼化反应。当使用Pd(Dba)_2/DMSO或Pd(Dba)_2-2AsPh3/KOAc/甲苯的组合时，在50度下进行区域和立体选择性的反应，得到烯丙基硼化合物。这些反应还可以容忍不同的官能团，如羰基。一个催化循环可能包括烯丙基亲电试剂与钯(0)络合物的氧化加成，二硼与钯(II)中间体之间的易金属化，以及烯丙基硼化合物的还原消除。(2)在以上(Pd(Dba)2/DMSO/50度)的优化条件下，双(频那多)二硼、烯丙基乙酸酯和醛的三组分反应顺利进行，导致了高产率的开环高烯丙醇。在Pd(Dba)2-2AsPh3催化剂存在下，烯丙基乙酸酯在甲苯中50度发生亲核硼化反应和100度分子内烯丙基硼化反应，得到高产率和高顺式立体选择性的环状高烯丙基醇。过渡金属催化3-烷氧基乙烯基硼烷异构化反应合成烯丙基硼化合物(1)在[Ir(COD)(PPh2Me)2]PF6和NiC12(PPh2Me)2催化剂存在下，3-烷氧基乙烯基硼烷立体选择性地进行异构化反应，分别得到E-和Z-烯丙基硼化合物。(2)具有羰基官能团的3-烷氧基乙烯基硼烷经催化异构化和分子内烯丙基化反应得到环醚。

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.