Faculté des sciences

Amino-Claisen Rearrangements and Diels-Alder Reactions of Ketene N,O-Acetals: Reactivity Studies. On the Way to a Novel Tandem Process?

Neuschütz, Klaus ; Simone, Jean-Mary ; Thyrann, Thomas ; Neier, Reinhard

In: Helvetica Chimica Acta, 2000, vol. 83, no. 10, p. 2712 - 2737

We report the synthesis of N-benzyl-N-[(E)-buta-1,3-dienyl]propanamide (6) and its corresponding O-silyl-substituted ketene N,O-acetal 7 and their Diels-Alder reaction. Propanamide 6 reacted smoothly, whereas the yield obtained from 7 was low, probably due to polymerization of the dienophile induced by electron transfer. The ketene... More

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    Summary
    We report the synthesis of N-benzyl-N-[(E)-buta-1,3-dienyl]propanamide (6) and its corresponding O-silyl-substituted ketene N,O-acetal 7 and their Diels-Alder reaction. Propanamide 6 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 β-lactam rac-34 were observed.