Efficient Synthesis of Enantioenriched Isoxazoles by Chirality Transfer in Gold‐Catalyzed Cyclization/Methylene‐Group Transfer Followed by Carbonyl Ene Reaction

摘要

> Enantioenriched isoxazoles having a chiral side chain at the 4‐position were efficiently synthesized by chirality transfer in a gold‐catalyzed cyclization/intermolecular methylene‐transfer sequence followed by a carbonyl ene reaction. The chiral information of the enantioenriched O ‐propargylic oximes was completely retained during the gold‐catalyzed reaction. The subsequent carbonyl ene reaction between the resulting 4‐methylenated isoxazoline and glyoxylates proceeded with excellent levels of chirality transfer by using BF ₃ · OEt ₂ as a Lewis acid. According to the relationship of absolute configuration between the starting propargylic oxime and the obtained alcohol having an isoxazole, the carbonyl ene reaction proceeded in an endo manner.