In the presence of a catalytic amount of a ruthenium complex coordinated with PBu3, alkynylstannanes (R1C≡CSnBu3) were found to accept the addition of terminal alkynes (R2C≡CH) with a 1,2-shift of the stannyl group to give (E)- and (Z)-1-tributylstannylbut-1-en-3-ynes (Bu3SnC(R1)=CHC≡CR2). Various combinations of substrates having an aromatic and/or aliphatic substituent can be used, and the stereochemical outcome depends largely on the character of these substituents. The reaction of aliphatic terminal alkynes proceeds stereoselectively, and substituent R1 on the alkynylstannanes determines the configuration: E for R1 = alkyl and Z for R1 = aryl. In contrast, the reaction of arylacetylenes gave a mixture of stereoisomers irrespective of the character of substituent R1 on the alkynylstannane. Ruthenium–β-stannylvinylidene complexes generated from a ruthenium complex and an alkynylstannane with migration of the stannyl group are likely to be key intermediates, which accept addition of the C–H bond of terminal alkynes to give the corresponding stannylenynes. DFT calculation clearly shows that the 1,2-shift of the stannyl group on formation of ruthenium–β-stannylvinylidene complexes is more facile than the corresponding 1,2-hydrogen shift of the coordinating terminal alkynes. The effect of the substituents on the stereoselectivity also is discussed based on the calculation.
在以PBu3配位的
钌络合物的催化作用下,炔基
锡烷(R1C≡CSnBu3)可以接受端炔(R2C≡CH)的加成,伴随
锡基团的1,2-迁移,生成(E)-和(Z)-1-三
丁基锡基丁-1-烯-3-炔(Bu3SnC(R1)=CHC≡CR2)。可以使用具有芳香和/或脂肪族取代基的各种底物组合,立体
化学结果主要取决于这些取代基的性质。脂肪族端炔的反应具有立体选择性,且炔基
锡烷上的取代基R1决定构型:R1为烷基时得到E构型,R1为芳基时得到Z构型。相比之下,芳基
乙炔的反应产生立体异构体的混合物,与炔基
锡烷上取代基R1的性质无关。由
钌络合物和炔基
锡烷经
锡基团迁移生成的
钌-β-
锡基亚甲基络合物可能是关键中间体,它们接受端炔的C-H键加成生成相应的
锡基烯炔。DFT计算清楚地表明,在形成
钌-β-
锡基亚甲基络合物时,
锡基团的1,2-迁移比配位端炔的相应1,2-氢迁移更容易进行。文中还基于计算讨论了取代基对立体选择性的影响。