探索了Ni(0)催化的CO 2(1 atm)与各种不对称二炔提供吡喃酮的环加成反应的区域选择性。当二炔上的一个末端取代基为甲基,另一个末端为中等或大尺寸时,使用1,3-双-(2,6-二异丙基苯基)-咪唑-2-亚烷基(IPr)具有很高的区域选择性(R L = i -Pr,t -Bu或TMS)。相比之下,仅当R L大(TMS)时,使用相对较小的N杂环卡宾1,3-二甲基咪唑-2-亚烷基(IMes)才具有较高的选择性。主要异构体的X-射线晶体分析表明,相对大ř大号组在所述吡喃酮的3-位。
An azole compound represented by the formula (I): ##STR1## wherein X is a nitrogen atom; Ar is a phenyl group substituted by halogen or a halogenated C.sub.1-4 alkyl group; R.sup.1 and R.sup.2 independently are a hydrogen atom or a lower alkyl group, or R.sup.1 and R.sup.2 may combine together to form a lower alkylene group; n denotes an integer of 0 to 2; and R.sup.7 is a hydrogen atom, a hydroxyl group which may be optionally acylated by an acyl group selected from acetyl, propionyl, butyryl, isobutyryl, phenylacetyl and benzoyl, or may form a bond together with R.sup.1 ; or a salt thereof.
A Ni‐catalyzed [2+2+2] cycloaddition reaction between allene‐ynes and various mono‐, di‐ and tri‐substituted allenes is described. This protocol effectively differentiates allenyl π components and shows broad substrate generality to give highly functionalized carbocycles. A DFT study played a key role in revealing a detailed reaction mechanism that controls site‐, regio‐ and stereoselectivity, which