School of Chemistry and Chemical Engineering, Guangxi University , Nanning 530004, People's Republic of China.
J Org Chem. 2013 Nov 1;78(21):10812-20. doi: 10.1021/jo4017748. Epub 2013 Oct 22.
The cycloisomerization of a bicyclo[4.1.0] substrate into 4,5-dihydrobenzo[b]furan was investigated by using density functional theory (DFT). Comparative studies on four models (model I: with W(CO)5 and NEt3; model II: without NEt3; model III: without W(CO)5; model IV: without W(CO)5 and NEt3) indicate that this reaction is the most likely to proceed under model I to give the product. The ring closure process is greatly associated with the H1 and H2 transfer processes, because in the H1 transfer process, the carbene C3 atom is mainly stabilized by W(CO)5, and in the H2 atom transfer process the C3 atom is mainly stabilized by the O1 atom. The rearrangement of 12 to give 14 is the rate-determining step of this reaction with a free energy barrier of 31.0 kcal/mol. The presence of W(CO)5 can not only promote the H1 transfer and the ring closure (1→6-[W]) but can also be slightly favorable for the isomerization of 6-[W] into 11-W. NEt3 mainly has an effect in the 6-[W]→11-[W] stage, in which it mainly plays proton-transfer bridge and proton-adsorption roles.
我们采用密度泛函理论（DFT）研究了双环[4.1.0]底物的环异构化反应生成 4,5-二氢苯并[b]呋喃的过程。对四个模型（模型 I：含 W(CO)5 和 NEt3；模型 II：不含 NEt3；模型 III：不含 W(CO)5；模型 IV：不含 W(CO)5 和 NEt3）进行了比较研究，结果表明，该反应最有可能在模型 I 下进行，生成产物。环闭合过程与 H1 和 H2 转移过程密切相关，因为在 H1 转移过程中，碳烯 C3 原子主要由 W(CO)5 稳定，而在 H2 原子转移过程中，C3 原子主要由 O1 原子稳定。12 重排生成 14 是该反应的决速步骤，自由能垒为 31.0 kcal/mol。W(CO)5 的存在不仅可以促进 H1 转移和环闭合（1→6-[W]），而且对 6-[W]异构化为 11-[W]（6-[W]→11-[W]）也有略微的促进作用。NEt3 主要在 6-[W]→11-[W]阶段起作用，主要起到质子转移桥和质子吸附的作用。
