title: Regioselective synthesis of 2,3,4- or 2,3,5-trisubstituted pyrroles via [3,3] or [1,3] rearrangements of O-vinyl oximes.
abstract: The regioselective synthesis of 2,3,4- or 2,3,5-trisubstituted pyrroles has been achieved via [3,3] and [1,3] sigmatropic rearrangements of O-vinyl oximes, respectively. Iridium-catalyzed isomerization of easily prepared O-allyl oximes enables rapid access to O-vinyl oximes. The regioselectivity of pyrrole formation can be controlled by either the identity of the α-substituent or through the addition of an amine base. When enolization is favored, a [3,3] rearrangement followed by a Paal-Knorr cyclization provides a 2,3,4-trisubstituted pyrrole; when enolization is disfavored, a [1,3] rearrangement occurs prior to enolization to produce a 2,3,5-trisubstituted pyrrole after cyclization. Optimization and scope of the O-allyl oxime isomerization and subsequent pyrrole formation are discussed and mechanistic pathways are proposed. Conditions are provided for selecting either the [3,3] rearrangement or the [1,3] rearrangement product with β-ester O-allyl oxime substrates.
authors: Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, MC 111, Chicago, Illinois 60607, USA.
authors: Heng-Yen
authors: HY
authors: Wang
authors: Daniel S
authors: DS
authors: Mueller
authors: Rachna M
authors: RM
authors: Sachwani
authors: Rachel
authors: R
authors: Kapadia
authors: Hannah N
authors: HN
authors: Londino
authors: Laura L
authors: LL
authors: Anderson
mesh_terms: D007659:Ketones / Q000737:chemistry; D010091:Oximes / Q000737:chemistry*; D011758:Pyrroles / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism; D013379:Substrate Specificity
chemical_list: D007659:Ketones; D010091:Oximes; D011758:Pyrroles