Synthesis of Pyrroles via Consecutive 6π-Electrocyclization/Ring-Contraction of Sulfilimines
Franz-Lucas Haut, Niklas J. Feichtinger, Immanuel Plangger, Lukas A. Wein, Mira Müller, Tim-Niclas Streit, Klaus Wurst, Maren Podewitz* and Thomas Magauer*
*Leopold-Franzens-University Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria,
Email: maren.podewitz
uibk.ac.at, thomas.magaueruibk.ac.at
F.-L. Haut, N. J. Feichtinger, I. Plangger, L. A. Wein, M. Müller, T.-N. Streit, K. Wurst, M. Podewitz, T. Magauer, J. Am. Chem. Soc., 2021, 143, 9002-9008.
DOI: 10.1021/jacs.1c04835
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Abstract
Ring-opening of readily available 2,5-dihydrothiophenes provides access to a panel of 1,3-dienes which undergo pyrrole formation in the presence of inexpensive chloramine-T trihydrate. The transformation is conducted in an open flask and proceeds at ambient temperatures.
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synthesis of precursors and reaction pathway
Pyrrole Formation
1,3-Diene (0.20 mmol, 1 equiv) was placed in a vial (max. 20 mL) and dissolved in a mixture of acetonitrile and hexafluoroisopropanol (9:1, 2.0 mL). Chloramine-T trihydrate (115 mg, 400 µmol, 2.00 equiv) was added portionwise over ten minutes at 23 °C. Upon full conversion of the starting material, indicated by TLC analysis (0.5-8 h), 3-chloroperbenzoic acid (77%, 44.8 mg, 0.20 mmol, 1.0 equiv) was added in one portion at 23 °C. After one hour, saturated aqueous sodium thiosulfate solution (20 mL) and ethyl acetate (20 mL) were added, the layers were separated and the aqueous phase was extracted with ethyl acetate (2 × 20 mL). The combined organic layers were washed with saturated aqueous sodium bicarbonate solution (20 mL) and dried over sodium sulfate. The dried solution was filtered, the filtrate was concentrated under reduced pressure and the crude product was purified by flash-column chromatography on silica gel to furnish pyrrole.
Note: The reaction was carried out without flame-drying the glassware and under air employing non-dried solvents (acetonitrile and hexafluoroisopropanol, HPLC-grade)
Key Words
ID: J48-Y2021
