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Asymmetric Annulation of Donor–Acceptor Cyclopropanes with Dienes

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posted on 01.07.2015, 00:00 by Hao Xu, Jiang-Lin Hu, Lijia Wang, Saihu Liao, Yong Tang
An efficient [4 + 3] cycloaddition reaction of D–A cyclopropanes with dienes has been successfully developed. The reaction proceeds well with various dienolsilyl ethers in the presence of Lewis acid, delivering a variety of cycloheptenes and [n,5,0]­carbobicycles with excellent stereoselectivity. The asymmetric version of this reaction is also realized using a newly designed chiral Cy-TOX ligand, providing a new approach to access optically active cycloheptenes and [n,5,0]­carbobicycles. Mechanisic study reveals that the reaction involves a stepwise pathway, which undergoes an unusual ring opening of five-membered [3 + 2] intermediate and sequential intramolecular cyclization to afford the thermodynamically stable [4 + 3] annulation product.