| Oxabridged-ring,especially seven-membered oxabridged-ring has attracted a great deal of interest in past few years for the reason that they are ubiquitous in a large number of natural products,synthetic molecules and versatile intermediates with important biological activity[1].Many strategies have been developed for their synthesis.For example,the[4+3]annulation between allyl cations and furans[2].[5+2]annulations between oxidopyrylium and alkenes[3].In addition,tandem catalysis cycloaddition have also been shown as an effective method.Despite the excellent progress have made,asymmetric stereoselective methods are still lacking.The way to efficiently construct single configuration oxabridged-ring from readily accessible precursors still remains a significant challenge.In 20th century chiral auxiliary approaches were introduced to resolve these issues.In 21th century,asymmetric organocatalysis method was introduced to construct seven-membered oxabridged-ring.Metal-catalyzed asymmetric reactions are relatively rare,Cu and Pt catalyzed highly enantioselective reaction have been developed well.As for gold catalyst,as far as we know,only one example for gold?I?-catalyzed synthesis of optically active oxabridged-ring has been developed by Lopez's group[4]to date Therefore,the development of efficient methods to access asymmetric oxabridged-ring are of great importance.The highly exo-and enantio-selective gold-catalyzed tandem heterocyclization/[4+3]cycloaddition of 2-?1-alkynyl?-2-alken-1-ones and 1,3-diphenyl-isobenzofuran was implemented by utilizing Ming-Phos,which provides a facile access to chiral seven-membered oxabridged-ring in 80-98%yield with high exo selectivity?exo:endo up to 50:1?and up to 97%ee.We also developed a series of chiral monophosphine ligands Yu-Phos in order to use them in asymmetric gold catalyst,but unfortunately no proper reaction have been found. |
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