Lam Heather, Qureshi Zafar, Wegmann Marcus, Lautens Mark
Davenport Laboratories, Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, M5S 3H6, Canada.
Angew Chem Int Ed Engl. 2018 Dec 3;57(49):16185-16189. doi: 10.1002/anie.201810760. Epub 2018 Nov 12.
Cycloadditions are powerful processes to synthesize complex polycyclic scaffolds. Herein, we disclose a [4+3]-cycloaddition between an in situ generated ortho-quinone methide and an isomünchnone to yield oxa-bridged oxazocine cores, generating N and H O as the sole by-products. Using only catalytic amounts of camphorsulfonic acid, it is possible to generate both reactive intermediates in one step, eliminating the need for rhodium catalysts generally employed for isomünchnone formation. Spectroscopic data and X-ray crystallography indicate the formation of the syn diastereomer, with the main side-product arising from a hydrate participating in a competing [4+2]-cycloaddition pathway.
环加成反应是合成复杂多环骨架的有力方法。在此，我们报道了原位生成的邻醌甲基化物与异氰酸酯之间的[4+3]环加成反应，生成氧桥连恶唑并环辛烷核心，仅产生N和H O作为副产物。仅使用催化量的樟脑磺酸，就可以一步生成两种反应中间体，无需通常用于异氰酸酯形成的铑催化剂。光谱数据和X射线晶体学表明形成了顺式非对映异构体，主要副产物来自参与竞争[4+2]环加成途径的水合物。
