title: Synthesis of pyrroles through a 4π-electrocyclic ring-closure reaction of 1-azapentadienyl cations.
abstract: 1-Azapenta-1,4-diene-3-ols 4a-m are easily accessible from 1-azapenta-1,4-dien-3-ones 3a-i and organolithium compounds. Treatment of the compounds 4a-m with strong acid (triflic acid) generates 1-azapentadienyl cations in situ upon protonation at the hydroxyl oxygen atom and subsequent water elimination. The intermediate cations undergo facile 4π-electrocyclization under ambient condition to give diversely substituted pyrroles 6a-m in moderate to good yield. The product pyrrole 6k could be characterized by X-ray diffraction. Quantum chemical calculations were performed to elucidate the mechanism of this reaction with respect to starting compounds, transition states, and products. They support the proposed mechanism of a 4π-conrotatory Möbius-type electrocyclic ring-closure reaction.
authors.affiliation: Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, D-48149 Münster, Germany.
authors.forename: Rishikesh
authors.initials: R
authors.lastname: Narayan
authors.forename: Roland
authors.initials: R
authors.lastname: Fröhlich
authors.forename: Ernst-Ulrich
authors.initials: EU
authors.lastname: Würthwein
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D003500:Cyclization; D006878:Hydroxides / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008698:Mesylates / Q000737:chemistry; D015394:Molecular Structure; D011090:Polyenes / Q000737:chemistry*; D011522:Protons; D011758:Pyrroles / Q000138:chemical synthesis*; D011789:Quantum Theory; D013237:Stereoisomerism; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D001372:Aza Compounds; D002412:Cations; D006878:Hydroxides; D008698:Mesylates; D011090:Polyenes; D011522:Protons; D011758:Pyrroles; C031356:hydroxide ion; C012077:trifluoromethanesulfonic acid