UPMC Univ Paris 06, IPCM UMR CNRS 7201, 4 Place Jussieu, 75005 Paris, France.
Chemistry. 2010 Aug 2;16(29):8904-13. doi: 10.1002/chem.201000486.
A variety of 1,6-heptadiynes and certain borylalkynes co-oligomerize with enol ethers in the presence of [CpCo(C(2)H(4))(2)] (Cp=cyclopentadienyl) to furnish the hitherto elusive acyclic 2:1 products, 1,3,5-trien-1-ol ethers, in preference to or in competition with the alternative pathway that leads to the standard [2+2+2] cycloadducts, 5-alkoxy-1,3-cyclohexadienes. Minor variations, such as lengthening the diyne tether, cause reversion to the standard mechanism. The trienes, including synthetically potent borylated derivatives, are generated with excellent levels of chemo-, regio-, and diastereoselectivity, and are obtained directly by decomplexation of the crude mixtures during chromatography. The cyclohexadienes are isolated as the corresponding dehydroalkoxylated arenes. In one example, even ethene functions as a linear cotrimerization partner. The alkoxytrienes are thermally labile with respect to 6pi-electrocyclization-elimination to give the same arenes that are the products of cycloaddition. The latter, regardless of the mechanism of their formation, can be viewed as the result of a formal [2+2+2] cyclization of the starting alkynes with acetylene. One-pot conditions for the exclusive formation of arenes are developed. DFT computations indicate that cyclohexadiene and triene formation share a common intermediate, a cobaltacycloheptadiene, from which reductive elimination and beta-hydride elimination compete.
各种 1,6-庚二炔和某些硼基炔在 [CpCo(C(2)H(4))(2)]（Cp=环戊二烯基）的存在下与烯醚共聚，以提供迄今难以捉摸的无环 2:1 产物 1,3,5-三烯-1-醇醚，优先于或与导致标准 [2+2+2] 环加成产物 5-烷氧基-1,3-环己二烯的替代途径竞争。微小的变化，如延长二炔键合，导致恢复到标准机制。这些三烯包括合成上有效的硼化衍生物，具有出色的化学选择性、区域选择性和非对映选择性生成，并且通过在色谱过程中直接从粗混合物中去络合即可获得。环己二烯被分离为相应的脱烷氧基芳烃。在一个例子中，甚至乙烯也作为线性共三聚化伙伴。烷氧基三烯对 6π-电环化消除是热不稳定的，以给出与环加成产物相同的芳烃。后者，无论其形成机制如何，都可以看作是起始炔烃与乙炔的正式 [2+2+2] 环化的结果。开发了专一地形成芳烃的一锅法条件。DFT 计算表明，环己二烯和三烯的形成共享一个共同的中间体，即钴环庚二烯，其中还原消除和β-氢消除竞争。
