Reactions of aminopentadienal derivatives with 5,6-dihydropyridinium saltsas an approach to manzamine alkaloids based upon biogenetic considerations

Recent results from our laboratory have prompted us to introduce a modifica tion of the original Baldwin proposal for the biosynthesis of manzamine alk aloids. In this new model, aminopentadienal derivatives of general structur es 2 or 3 can not only cyclize to give pyridinium salts such as cyclostelle ttamines but also react with 5,6-dihydropyridinium salts 1 leading to speci es such as 6 or 7, which would be key intermediates in the syntheses of man zamine A and halicyclamine B. On the basis of the chemistry depicted in Sch eme 2, model reactions of dienes 9, 10, 12; and 13 with salts 1 have been i nvestigated. Diene 9 gave an interesting rearrangement product 15a, while d ienes 10 and 12 gave halicyclamine- and manzamine-type adducts 19 and 23, r espectively. In addition, glutaconaldehyde derivative 13 gave adduct 32 pos sessing some characteristic features of sarain A.