title: Four mechanisms in the reactions of 3-aminopyrrole with 1,3,5-triazines: inverse electron demand Diels-Alder cycloadditions vs S(N)Ar reactions via uncatalyzed and acid-catalyzed pathways.
abstract: Reaction of 3-aminopyrrole with seven 1,3,5-triazines was studied in a one-step reaction (in situ formation of 3-aminopyrrole) and a two-step reaction (using the tetraphenylborate salt and an amine base). An inverse-electron demand Diels-Alder reaction (IEDDA) was observed with R1 = CF3, CO2Et, and H with the formation of 5H-pyrrolo[3,2-d]pyrimidine derivatives. S(N)Ar was observed when 2,4,6-trifluoro- or 2,4,6-trichloro-1,3,5-triazine were used--1,3,5-triazines that had leaving groups. If excess 1,3,5-triazine was present the initial S(N)Ar product reacted further, in the presence of acid and water, with another equivalent of 1,3,5-triazine to give compounds containing three linked heterocyclic rings. No reaction was observed with R1 = C6H5 and OCH3. Four mechanisms are proposed to explain the experimental results: uncatalyzed and acid catalyzed inverse electron demand Diels-Alder cascades leading to cycloaddition, and uncatalyzed and acid-catalyzed S(N)Ar reactions leading, respectively, to single and double substitution products. Acid catalysis was a factor when there was reduced reactivity in either reactant.
authors.affiliation: Department of Chemistry, Penn State Brandywine, 25 Yearsley Mill Road, Media, Pennsylvania 19063, USA. MXD19@psu.edu
authors.forename: Michael
authors.initials: M
authors.lastname: De Rosa
authors.forename: David
authors.initials: D
authors.lastname: Arnold
authors.forename: Douglas
authors.initials: D
authors.lastname: Hartline
mesh_terms: D000143:Acids / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D004583:Electrons; D015394:Molecular Structure; D011758:Pyrroles / Q000737:chemistry*; D014227:Triazines / Q000737:chemistry*
chemical_list: D000143:Acids; D011758:Pyrroles; D014227:Triazines