Synthesis of Pyrroles via [3,3]-Rearrangement and Paal-Knorr Reaction

Significance

Reported is the synthesis of 2,4- and 2,3,4-substituted pyrroles via [3,3]-sigmatropic rearrangement and subsequent Paal-Knorr reaction. The iridium-catalyzed isomerization products 1 were isolated with vinyl E/Z ratios of approximately 1:2. The Paal-Knorr intermediate A was identified by NMR spectroscopy. The target pyrroles may also be afforded in a one-pot reaction in yields comparable to those obtained in the two-step procedure. Interestingly, as long as R^² = CN, the reaction proceeded directly from O-allyl oximes to pyrroles without the need for molecular sieves at lower temperature (25 ˚C).