An Unprecedented Pseudo-[3+2] Annulation between N-(4-Methoxyphenyl)aldimines and Aqueous Glutaraldehyde: Direct Synthesis of Pyrrole-2,4-dialdehydes

A new method for the direct one-pot synthesis of substituted pyrrole-2,4-dialdehdyes was developed. This overall pseudo-[3+2]-annulation reaction between glutaraldehyde and N-(4-methoxyphenyl)aldimines proceeds through proline-catalyzed direct Mannich reaction/cyclization, followed by 2-iodoxybenzoic acid mediated oxidative rearrangement of the in situ generated intermediate to give pyrrole-2,4-dialdehydes in high yields (up to 80 %).