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    Amino-Claisen rearrangements and Diels-Alder reactions of ketene N,O-acetals: Reactivity studies. On the way to a novel tandem process?
    (2000-1-12)
    Neuschutz, Klaus
    ;
    Simone, Jean-Mary
    ;
    Thyrann, Thomas
    ;
    We report the synthesis of N-benzyl-N-[(E)-buta-1,3-dienyl]propanamide (6) and its corresponding O-silyl-subitituted ketene N,O-acetal 7 and their Diels-Alder reaction. Propanamide G reacted smoothly, whereas the yield obtained from 7 was low, probably due to polymerization of the dienophile induced by electron transfer. The ketene N,O-acetals 27a-g were synthesized starting from the corresponding benzamides 25a-e (Scheme 9). The ketene N,O-acetals 27a-g showed increased stabilities and underwent amino-Claisen rearrangements under thermal conditions. Using catalysts, interesting side reactions leading either to the annulated systems, rac-35-37 or to a beta -lactam rac-34 were observed.