5-Aminopenta-2,4-dienals: Synthesis, Activation towards Nucleophiles, Molecular Modeling and Biosynthetic Implications in Relation to the Manzamine Alkaloids

Substituted 5-aminopentadienals and glutaconaldehydes are key elements postulated in the biosynthesis of the diverse class of manzamine-type alkaloids. The activation of 5-aminopentadienals into electrophilic iminium salts and their subsequent reactivity towards various nucleophiles has permitted the synthesis of a series of unsaturated compounds sometimes accompanied by cascades of rearrangements. Molecular modeling of these systems carried out using DFT calculations of HOMO/LUMO was in agreement with the experimental results indicating that strong electrophilic agents, such as POCl3 are required to turn 5-aminopentadienals into electrophiles. New examples of glutaconaldehyde reactivity, especially towards pyridinium salts, are presented and biosynthetic considerations are kept in mind throughout this study.