A synthesis of (+)-hypoxylactone has been accomplished in four steps starting from the allenoate γ-addition of threo-3-chloro-2-silyoxybutanals, leading to the revision of stereochemistry. The key was the discovery of control elements required to matching/mismatching cases in the allenoate γaddition to provide the desired adducts as a single isomer. The utility of the γ-adduct was demonstrated with the Au(I)-catalyzed cyclization to afford (+)-xylogiblactone A. Use of Ag 2 O was the key to epoxidation for preventing epimerization of the γ-lactone ring.
Stereoselective carbocyclizations of vinyloxiranes were efficiently catalyzed by Lewis acids to provide cyclic homoallyl alcohols as single isomers. The choice of Lewis acid, B(C6F5)3 was crucial for the stereoselective transformation in the case of cis vinyloxiranes, whereas BF3∙OEt2 was proven to be an effective catalyst for trans substrates. The method was well implemented in the synthesis of seven‐membered rings and six‐membered rings with functional group tolerance. Utility of the resulting trans‐ and cis homoallyl alcohols was demonstrated to concisely build the tricyclic core of musellarin A and E.
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