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With pyrrole (pKa17.5) and indole (pKa16.2) (entries 8–9), we mainly observe the formation of a mixture of allene oligomeric products. N-allyl indole has been obtained in only 16% yield after chromatography. A possible explanation means the intermediate ylide 6 (see Scheme 3) is not basic enough to deprotonate the azole. As a consequence, the acid– base reaction competes unfavorably with the polymerization of allene.8An excess oftriphenylphosphinedoesnot improve the yields. In an attempt to rationalize all these results, the following mechanism can be proposed (Scheme 3). The catalytic cycle might be initiated by a nucleophilic addition of triphenylphosphine to the electron-deficient allene 2. The enolate 6 then deprotonates the azole 1 generating the nucleophilic species 5 and the vinylphosphonium 4. Consecutively, nucleophilic addition of 5 to vinylphos- phonium 4 leads to the ylide 7. Finally, enolate 8 is obtained by prototropy and then undergoes a b-elimination affording the final g-addition allylazole 3 and regenerating the nucleophilic catalyst. |
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| 與吡咯(pKa17.5)和吲哚(pKa16.2)(條目8 - 9)我們主要觀察丙二烯的混合物的形成低聚物的產(chǎn)品。N-allyl吲哚獲得色譜法后16%的收益率。一個可能的解釋方面是指中間6(見方案3)不是最基本的足以deprotonate唑。因此,酸-基地與聚合反應(yīng)競爭來說是不利的丙二烯。8超額oftriphenylphosphinedoesnot改善的產(chǎn)量。為了理順這些結(jié)果,下面的機制可以提出(方案3)催化周期可能會發(fā)起一個親核加成的三苯基膦丙二烯2缺電子。的烯醇化物6然后deprotonates唑1生成親核物種5和vinylphosphonium 4。連續(xù),親核加成vinylphos - 5phonium 4方面導(dǎo)致了7。最后,烯醇化物8是一個b-elimination prototropy然后獲得的經(jīng)歷提供最終g-addition allylazole 3和再生的親核催化劑。 |
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