Controlling cyclizations of 2-pyrrolecarboxamidoacetals. Facile solvation of β-amido aldehydes and revised structure of synthetic homolongamide

Pyrrole N–C and C–C bond-forming cyclizations are described with 2-pyrrolecarboxamidoacetals 1–3 under standard acetal deprotection conditions (pTsOH/H2O) and with methanesulfonic acid. Under the former, N–C cyclization provided fused bi- and tricyclic systems bearing five- or six-membered rings, while the latter produced six- and seven-membered C–C cyclized products. Furthermore, an alternative structure for homolongamide 10 is proposed and is based on the facile solvation of β-amido aldehyde 7.