Trost Barry M, Rudd Michael T
Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
J Am Chem Soc. 2003 Sep 24;125(38):11516-7. doi: 10.1021/ja036410f.
The cycloisomerization of diyne-ols catalyzed by [CpRu(CH3CN)3]PF6 to 2-vinyl-1-acylcycloalkenes proceeds via a ruthenacyclopentadiene involving initial ionization of the tertiary or secondary alcohol, followed by readdition. In the case of primary alcohols, a competing pathway wherein water first adds would appear to occur. The feasibility of this proposed minor pathway was tested in the reaction of diynes in the presence of water. Quite excitingly, cyclization comcommittant with addition of water to form 1-acylcycloalkenes occurs. This proves to be general process to form five- and six-membered rings. Interestingly, hydrative cyclization of Z-5-decen-2,8-diyne to 1-acetyl-2-ethyl-cyclohexa-1,4-diene occurs without isomerization of the double bonds. Furthermore, the epoxide of the same substrate cyclizes without opening of the strained epoxide. Unsymmetrically substituted diynes cyclize with remarkable chemoselectivity wherein water attacks the less hindered alkynes. beta-branching of any kind gives only a single product. Remarkably, even competing methyl versus ethyl still effects a 2.5:1 selectivity in favoring water addition to the methyl-bearing alkyne. Alcohols can replace water and provide enol ethers. Strong mechanistic evidence suggests two reaction manifolds indeed operate, depending upon the presence of propargyl alcohols and the degree of substitution on the hydroxyl-bearing carbon.
由[CpRu(CH3CN)3]PF6催化的二炔醇环异构化生成2-乙烯基-1-酰基环烯烃的反应，是通过一个钌环戊二烯中间体进行的，该过程涉及叔醇或仲醇的初始电离，随后是再加成。对于伯醇，似乎会出现一条竞争途径，即水首先加成。在有水存在的情况下，通过二炔的反应对这一提出的次要途径的可行性进行了测试。非常令人兴奋的是，会发生与水加成同时进行的环化反应，生成1-酰基环烯烃。事实证明，这是形成五元环和六元环的普遍过程。有趣的是，Z-5-癸烯-2,8-二炔的水合环化反应生成1-乙酰基-2-乙基-环己-1,4-二烯，且双键没有异构化。此外，同一底物的环氧化物在环化时，张力环氧化物没有开环。不对称取代的二炔以显著的化学选择性进行环化反应，其中水进攻位阻较小的炔烃。任何类型的β-支链只生成单一产物。值得注意的是，即使是甲基与乙基的竞争，在水加成到含甲基的炔烃上时，仍表现出2.5:1的选择性。醇可以取代水并生成烯醇醚。有力的机理证据表明，实际上存在两种反应路径，这取决于炔丙醇的存在以及含羟基碳上的取代程度。
