Synthesis and Reactivity of Electron-Poor 2-Azadienes. Cycloaddition Reactions with Alkenes and Enamines

Article abstract of DOI:10.1021/jo00113a017

Electron deficient 2-azadienes derived from β-amino acids 3 are obtained by aza-Wittig reaction of N-vinylic phosphazenes 4 with carbonyl compounds.Inverse electron demand Diels-Alder reaction of azadienes 3 with trans-cyclooctene 7 and cis,trans-cyclooctadiene 8 leads to the formation of trans-cycloalkanotetrahydropyridines 10.Heterodienes 3 also react with enamines 13, 14, and 18 affording pyridine derivatives 16, 17, and 20 in a regioselective fashion.Norbornadiene 11, a less strained olefin than cycloalkenes 7 and 8, requires the presence of lithium perchlorate as catalyst in a nonaqueous solvent like ether, to give cycloadducts 12.