Tetronamides as Latent Acyclic Vinylogous Amides in Formal Aza‐[3 + 3] Cycloaddition Reactions with α,β‐Unsaturated Iminium Salts. An Unexpected Rearrangement and an Approach to Synthesis of Substituted Piperidines.

Abstract

Fused pyridine derivatives R 0450Tetronamides as Latent Acyclic Vinylogous Amides in Formal Aza-[3 + 3] Cycloaddition Reactions with α,β-Unsaturated Iminium Salts. An Unexpected Rearrangement and an Approach to Synthesis of Substituted Piperidines. -It is found that the temperature strongly affects the outcome of the [3 + 3] cycloadditions. When it is less than 130°C, the expected cycloadducts of type (III) and (VIII) are mainly formed, while at 150 < t < 220°C, considerable amounts of head-to tail regioisomers like (IV) and (IX) are isolated. The latter were found in previous studies. At higher temperature 220°C, rearrangement of the expected cycloadducts to pyridine derivatives of type (V) or (XII) takes place. The cycloaddition proceeds without stereoselectivity and the products can smoothly be transformed into substituted piperidines. -(SYDORENKO, N.; HSUNG*, R. P.; DARWISH, O. S.; HAHN, J. M.; LIU, J.; J.