Trost Barry M, Rhee Young Ho
Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA.
J Am Chem Soc. 2003 Jun 25;125(25):7482-3. doi: 10.1021/ja0344258.
The ability to form rhodium-vinylidene complexes in situ from terminal alkynes has led to the development of a catalytic process, the cycloisomerization of homopropargylic and bis-homopropargylic alcohols to dihydrofurans and dihydropyrans. Among the transition metals that perform similar reactions, rhodium catalysts demonstrate the best chemoselectivity and turnover numbers to date. Both secondary and tertiary alcohols participate equally well. The presence of proparylic oxygen and nitrogen functionality, which potentially can be induced to ionize via formation of allenylidene metal complexes, is compatible with this catalyst. The formation of a 5-amino-dihydropyran which is not compatible with some of the previous catalysts proceeds in good yield with the rhodium catalysts. A substrate bearing a benzylic hydroxyl group adjacent to an electron-rich aromatic ring also participates without complications of ionization. The method provides access to useful aminosugars. A mechanism to account for the different selectivity of this catalyst as compared to others is proposed.
由末端炔烃原位形成铑-亚乙烯基配合物的能力推动了一种催化过程的发展，即高炔丙基醇和双高炔丙基醇环异构化为二氢呋喃和二氢吡喃。在能进行类似反应的过渡金属中，铑催化剂迄今为止表现出最佳的化学选择性和转化率。仲醇和叔醇的参与效果同样良好。炔丙基氧和氮官能团的存在（其有可能通过亚联烯基金属配合物的形成而被诱导电离）与这种催化剂兼容。对于一些先前的催化剂而言不兼容的5-氨基-二氢吡喃的形成，使用铑催化剂时产率良好。在富电子芳环相邻位置带有苄基羟基的底物也能参与反应，且不存在电离的复杂情况。该方法可用于制备有用的氨基糖。文中提出了一种机制来解释这种催化剂与其他催化剂相比具有不同选择性的原因。
