Synthesis of [<i>n</i>,5]-Spiroketals by Ring Enlargement of Donor-Acceptor-Substituted Cyclopropane Derivatives
作者:Christian Brand、Gesche Rauch、Michele Zanoni、Birger Dittrich、Daniel B. Werz
DOI:10.1021/jo901902g
日期:2009.11.20
three-membered ring with an oxygen donor and a carbonyl acceptor group into the five-membered enol ether system. Catalytic amounts of the Lewis acid Yb(OTf)3 facilitate the ring enlargement and increase the yield of the corresponding spiroketal in many cases. When Yb(OTf)3 was used, our experiments revealed an open transition state rather than a concerted mechanism because the stereochemistry of the spirocenter