Enantioselective Construction of Chiral Cyclopropa[c]coumarins via Lewis Base-Catalyzed Cyclopropanation
Jun-Chao Sun1, Xiao-Hui Wang1, Cong-Bin Ji2
1Key Laboratory of Small Functional Organic Molecule, Ministry of Education and Jiangxi Key Laboratory of Green Chemistry, Jiangxi Normal University, Nanchang, Jiangxi 330022, China.
Abstract:
The first highly enantioselective construction of chiral cyclopropa[c]coumarins was described. Using commercially available (bis)cinchona alkaloid (DHQ)2PYR as the chiral Lewis base catalyst, together with Cs2CO3 as the achiral base, the reaction of a series of coumarin-3-carboxylate and 3-benzoyl coumarins with tert-butyl 2-bromoacetate could give rise to the corresponding cyclopropa[c]coumarins bearing three continuous chiral stereocenters in 83-93% ee and 90-97% ee, respectively. The reaction is proposed to proceed via an in situ generated ammonium ylide intermediate.
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