Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking University , Beijing 100871, China.
J Am Chem Soc. 2013 Sep 11;135(36):13502-11. doi: 10.1021/ja4058844. Epub 2013 Sep 3.
Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, β-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate, which is supported by DFT calculations. The palladium carbene character of the key intermediate is validated by three aspects, including bond lengths, Wiberg bond order indices, and molecular orbitals, by comparison to those reported for stable palladium carbene species. Computational studies also revealed that the rate-limiting step is ene-yne-ketone cyclization, which leads to the formation of the palladium (2-furyl)carbene, while the subsequent carbene migratory insertion is a facile process with a low energy barrier (<5 kcal/mol).
钯催化的苄基、芳基或烯丙基溴化物与共轭烯-炔-酮之间的交叉偶联反应生成 2-烯基取代的呋喃。这种新颖的偶联反应涉及氧化加成、炔烃活化-环化、钯卡宾迁移插入、β-氢消除和催化剂再生。钯（2-呋喃基）卡宾被提出是关键中间体，这一观点得到了 DFT 计算的支持。通过与稳定的钯卡宾物种的键长、Wiberg 键序指数和分子轨道等方面的比较，验证了关键中间体的钯卡宾特征。计算研究还表明，速率限制步骤是烯-炔-酮的环化，这导致钯（2-呋喃基）卡宾的形成，而随后的卡宾迁移插入是一个容易的过程，具有较低的能量势垒（<5 kcal/mol）。
