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Iminium Catalysis with α-Alkyl Acroleins
T. Kano, Y. Tanaka, K. Osawa, T. Yurino, K. Maruoka*
Graduate School of Science, Kyoto University, Japan
23 March 2009 (online)
An organocatalytic asymmetric Diels-Alder reaction of α-alkyl-substituted acroleins 1 with cyclopentadiene (2) is reported. The TfOH salt of BINAM (1,1′-binaphthyl-2,2′-diamine) derivative 3 bearing bulky 3,5-di-tert-butyl phenyl substituents at the 3,3′-positions was found to mediate the reaction efficiently. A concise synthetic route to targets like 3 has earlier been described by the same group (J. Org. Chem. 2008, 73, 7387). exo-Diels-Alder products 4 bearing an all-carbon quaternary stereocenter were obtained in moderate to good yields and, except for methacrolein, good to high enantioselectivities. Moreover, examples of the use of an α,β-disubstituted acrolein as well as an acylic diene are included.