State Key Laboratory of Chemical Resource Engineering and Department of Organic Chemistry, Faculty of Science, Beijing University of Chemical Technology, Beijing 100029, China.
Org Biomol Chem. 2011 Sep 7;9(17):5997-6003. doi: 10.1039/c1ob05254c. Epub 2011 Jul 15.
A metal-free and formal [2 + 2 + 2] cycloaddition of triynes has emerged recently as a novel methodology for the synthesis of fused tricyclic compounds via an intramolecular cascade propargylic ene reaction, Diels-Alder cycloaddition and tautomerization. DFT calculations on three model systems reveal that the ene reaction with low distortion energy makes the metal-free strategy feasible and, as the rate-determining step, affects the regioselectivity of unsymmetric triynes. Furthermore, the types of final products depend on H-transfer during tautomerization after the Diels-Alder reaction. Generally, the different tethered atoms between the yne moieties are responsible for the different regioselectivities and the final products in the [2 + 2 + 2] cycloadditions. On the basis of a comprehensive theoretical investigation into the mechanism, triynes involving cyclic ynes have been designed and are predicted to react to afford fused tetracyclic products under milder conditions due to dramatically lower energy barriers and by altering the rate-determining step to the Diels-Alder reaction.
最近，一种无金属的[2+2+2]三炔环加成反应已经成为一种新颖的方法，通过分子内级联炔丙基烯反应、Diels-Alder 环加成和互变异构化来合成稠合的三环化合物。对三个模型体系的密度泛函理论（DFT）计算表明，烯反应具有较低的扭曲能，使得无金属策略成为可行的，并且作为速率决定步骤，影响不对称三炔的区域选择性。此外，最终产物的类型取决于 Diels-Alder 反应后互变异构化过程中的 H 转移。通常，炔基之间的不同连接原子负责[2+2+2]环加成反应中不同的区域选择性和最终产物。基于对反应机制的全面理论研究，设计了涉及环状炔的三炔，并预测在温和条件下反应生成稠合的四环产物，因为能量势垒显著降低，并通过改变速率决定步骤为 Diels-Alder 反应。
