酮-烯醇互变异构控制酸催化的罗宾逊环化法-DFT研究,ChemistrySelect

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酮-烯醇互变异构控制酸催化的罗宾逊环化法-DFT研究
ChemistrySelect ( IF 1.9 ) Pub Date : 2019-05-01 , DOI: 10.1002/slct.201900338
Shinichi Yamabe ₁ , Noriko Tsuchida ₂ , Shoko Yamazaki ₁

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通过DFT计算研究了三个鲁滨逊环化反应（A），（B）和（C）。（A）是催化的一个，基站，其中环己酮，OH甲基乙烯基酮（MVK）和^-（H ₂ O）₇被用作反应物。获得了八个基本步骤。第二过渡态TS2（A）是由次级轨道相互作用引起的迈克尔加成，而TS5（A）是醛醇缩合的。E1cB的第二个TS，TS8（A）具有相当大的活化能，这会使二酮A-4和酮醇A-7可被检测到。（B）是酸催化的反应，其中2-甲基环己酮，MVK和H ₃ O ⁺（H ₂ O）₇被用作反应物。获得了七个基本步骤。B‐2至B‐7中的所有中间体均为中性物种（未质子化）。质子转移辅助的酮-烯醇互变异构作用涉及所有TS。（C）是中性反应，其中2-甲基环戊烷-1,3-二酮，1-氯-3-戊酮和（H ₂ O）₈是反应物。第一C-C键的形成是由亲核取代（S带来_Ñ 2），其中离去基团为氯离子。伴随产生的H ₃ O ⁺用作酸催化剂以促进随后的过程。同样，在所有TS中都涉及酮-烯醇互变异构。

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Keto‐Enol Tautomerization Controls the Acid‐Catalyzed Robinson Annulation ‐ A DFT Study

Three Robinson annulation reactions (A), (B) and (C) were investigated by DFT calculations. (A) is a base catalyzed one, where cyclohexanone, methyl vinyl ketone (MVK) and OH⁻(H₂O)₇ were employed as reactants. Eight elementary steps were obtained. The second transition state, TS2(A), is of the Michael addition prompted by the secondary orbital interaction, and TS5(A) is of the aldol condensation. The second TS of E1cB, TS8(A), has an appreciable activation energy, which would make the diketone A‐4 and ketol A‐7 detectable species. (B) is an acid catalyzed reaction, where 2‐methylcyclohexanone, MVK and H₃O⁺(H₂O)₇ were adopted as reactants. Seven elementary steps were obtained. All the intermediates in B‐2 to B‐7 are neutral species (not protonated). The keto‐enol tautomerization assisted by the proton transfer is involved in all TSs. (C) is a neutral reaction, where 2‐methylcyclopentane‐1,3‐dione, 1‐chloro‐3‐pentanone and (H₂O)₈ were reactants. The first C−C bond formation is brought about by the nucleophilic substitution (S_N2) where the leaving group is the chloride ion. The concomitantly generated H₃O⁺ works as the acid catalyst to promote the subsequent processes. Again, the keto‐enol tautomerization is involved in all TSs.

更新日期：2019-05-01

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