Isakovic L, Ashenhurst J A, Gleason J L
Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, Quebec, Canada, H3A 2K6.
Org Lett. 2001 Dec 27;3(26):4189-92. doi: 10.1021/ol016814h.
The carbocyclic core of CP-225,917 and CP-263,114 is accessible through the [6+4] cycloaddition of a tropone with a 2-substituted cyclopentadiene. Examination of this reaction has revealed for the first time that this cycloaddition process is catalyzed by Lewis acids, including lanthanide triflates. Cycloadditions of several mono-, di-, and trisubstituted tropones with 2-silyloxycyclopentadienes using ZnCl(2) catalysis are found to proceed in good yield and, in many cases, with excellent diastereoselectivity. Subsequent transformation to the core of the CP-molecules involves a site-selective Baeyer-Villiger oxidation of a tricyclic diketone, followed by a syn-elimination process. [reaction: see text]
CP - 225,917和CP - 263,114的碳环核心可通过氧杂环庚三烯与2 - 取代环戊二烯的[6 + 4]环加成反应得到。对该反应的研究首次揭示，这种环加成过程是由路易斯酸催化的，包括镧系三氟甲磺酸盐。使用ZnCl₂催化，几种单取代、二取代和三取代的氧杂环庚三烯与2 - 硅氧基环戊二烯的环加成反应产率良好，并且在许多情况下具有优异的非对映选择性。随后向CP - 分子核心的转化涉及三环二酮的位点选择性拜耳 - 维利格氧化，然后是顺式消除过程。[反应：见正文]
