Amino acids, XI: (±)Pipecolic acid derivatives - Part 1: The [4+2] cycloaddition pathway

Article abstract of DOI:10.1002/ardp.19923250708

[4+2] Cycloadditions of various dienes 1 with the acceptor-subtituted imines 2 furnished the 4-oxo-piperidine-2.2-dicarboxylate derivatives 3, 5, 11, 12. All efforts to get the regio-isomeric 5-oxo-derivatives (Scheme 2) by variation of the reaction condi