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[3+2] Annulation of MBH Adducts Promoted by Bifunctional Phosphines
F. Zhong, X. Han, Y. Wang, Y. Lu*
National University of Singapore, Singapore and Henan University, Kaifeng, P. R. of China
19 August 2011 (online)
Lu and co-workers report a highly enantioselective [3+2] annulation of MBH adducts 2 and isatin-derived activated alkenes 1. The reactions were promoted by bifunctional phosphine 3, which is easily accessible from threonine. Instead of commonly employed allenes and alkynes for [3+2] cycloadditions, the authors applied MBH adducts 2 as a C3 synthon. The obtained spirooxindoles 4 posses two contiguous quaternary centers with various functional groups. Also, a one-pot procedure with N-PMB-isatin and malononitrile under the reaction condition affords the desired product 4 with the same reactivity and enantioselectivity.