Rapid and Enantioselective Synthetic Approaches to Germanicol and Other Pentacyclic Triterpenes
作者:Karavadhi Surendra、E. J. Corey
DOI:10.1021/ja802730a
日期:2008.7.1
routes to the key intermediate 2 for the synthesis of the pentacyclic triterpene germanicol 1 have been developed. In the first, the ( S)-epoxide of farnesyl bromide is transformed in just three steps to the tetracyclic intermediate 7, which is converted to chiral 2 by treatment with polyphosphoric acid. The second synthetic route to 2 involves the coupling of the ( S)-epoxide 8 with vinyl iodide 9 to give
An arene-terminated epoxy olefin cyclization was promoted by a water-tolerant Lewis acid to give tri- and tetracyclic 3β-hydroxy terpenoids and steroid derivatives in 57 and 37% yields, respectively, per new formed ring up to 75%.