An expeditious microwave-induced synthesis of pyrroles using commercially available 2,5- dimethoxytetrahydrofuran and primary amines in the presence of ammonium chloride has been achieved in excellent yield

Bandyopadhyay, Debasish

Banik, Bimal K.

English

Scholarworks@UTRGV Univ. of Texas RioGrande Valley

University of Texas Rio Grande Valley ScholarWorks @ UTRGV Chemistry Faculty Publications and Presentations College of Sciences 2017 MICROWAVE-INDUCED PAAL-KNORR REACTION WITH AMMONIUM CHLORIDE: SYNTHESIS OF PYRROLES Debasish Bandyopadhyay The University of Texas Rio Grande Valley Bimal K. Banik The University of Texas Rio Grande Valley Follow this and additional works at: https://scholarworks.utrgv.edu/chem_fac  Part of the Chemistry Commons Recommended Citation Bandyopadhyay, D., & Banik, B. K. (2017). MICROWAVE-INDUCED PAAL-KNORR REACTION WITH AMMONIUM CHLORIDE: SYNTHESIS OF PYRROLES. Heterocyclic Letters, 7(2), 473–474. This Article is brought to you for free and open access by the College of Sciences at ScholarWorks @ UTRGV. It has been accepted for inclusion in Chemistry Faculty Publications and Presentations by an authorized administrator of ScholarWorks @ UTRGV. For more information, please contact justin.white@utrgv.edu, william.flores01@utrgv.edu. 473    Heterocyclic Letters                                                                                                               Vol. 7| No.2|473-474|Feb-April| 2017           ISSN : (print) 2231–3087 / (online) 2230-9632  CODEN: HLEEAI http://heteroletters.org   MICROWAVE-INDUCED PAAL-KNORR REACTION WITH AMMONIUM CHLORIDE: SYNTHESIS OF PYRROLES   Debasish Bandyopadhyaya and Bimal K. Banika, b*  aDepartment of Chemistry, University of Texas-Pan American, 1201 W. University Dr., Edinburg, TX 78539 USA; bCurrent address: 3135 South Sugar Road, Edinburg, TX 78539 USA; bimalbanik10@gmail.com and bimal.banik@chsst.org   Abstract  An expeditious microwave-induced synthesis of pyrroles using commercially available 2,5-dimethoxytetrahydrofuran and primary amines in the presence of ammonium chloride has been achieved in excellent yield.   Key words  Ammonium chloride, Pyrrole, Microwave irradiation, Dimethoxytetrahydrofuran  Introduction  Pyrroles are present in many natural and non-natural products and they have various medicinal properties. Primary amines on reaction with dicarbonyl compound in the presence of acidic catalysts can produce pyrroles and this reaction is called Paal-Knorr reaction [1]. Pyrroles can also be synthesized by numerous other ways [2]. We reported a simple procedure for the preparation of N-substituted pyrroles via NBS-catalyzed reactions of primary amines with 2,5-dimethoxytetrahydrofuran [1].  Our investigation in this area uncovered an expeditious ammonium chloride-mediated method for the synthesis of pyrroles starting from primary amines and 2,5-dimethoxytetrahydrofuran. This reaction is environmentally benign and excellent for the preparation of N-substituted pyrroles [3].   Results and Discussions   The dialdehyde that is necessary for the preparation of pyrroles can be obtained in the reaction media by treatment of 2,5-dimethoxytetrahydrofuran with an acidic reagent. Ammonium chloride in the presence of microwave irradiation can generate the active dialdehyde. Therefore, reaction of 2,5-dimethoxytetrahydrofuran (1.1 mmol) and aromatic amine (1 mmol) in the presence of ammonium chloride (200 mg, 3.73 mmol) was performed in an automated microwave oven in the absence of any solvent.  Surprisingly, this reaction produced N-substituted pyrrole as the only product in excellent yield within 5-8 min of microwave irradiation (Table 1). Various pyrroles were made following this procedure.     Bimal K. Banik et al. / Heterocyclic Letters Vol. 7| No.2|473-474|Feb-April| 2017  474  Table 1: Ammonium Chloride-Mediated Synthesis of N-Substituted Pyrroles  Entry      Starting Compounds   Products         Yield(%) 1       2,5-Dimethoxytetrahydrofuran and aniline          N-Phenylpyrrole   93 2        2,5-Dimethoxytetrahydrofuran and 4-methoxyaniline    N-4-Methoxyphenylpyrrole             90 3        2,5-Dimethoxytetrahydrofuran and 4-methylaniline       N-4-Methylphenylpyrrole  89 4       2,5-Dimethoxytetrahydrofuran and allylamine         N-Allylpyrrole   90 5        2,5-Dimethoxytetrahydrofuran and benzylamine         N-Benzylpyrrole   90 Ammonium chloride under microwave irradiation produces hydrochloric acid and this liberated acid generates the reactive dialdehyde. Reaction of 1,4-dialdehyde with primary amine under acidic conditions is known to produce pyrroles[1].  Experimental  The reaction mixture was irradiated in an automated microwave at 500C and 300 watt power level. The reaction mixture was extracted with dichloromethane (10 mL), the organic layer was washed with water  (5 mL), dried over sodium sulfate (2 gm), evaporated and purified through a short column of silica gel. The products are all known. Time required for the reaction (Table 1: entry 1, 8 min; entry 2, 6 min; entry 3, 6 min; entry 4, 6 min and entry 5, 5 min). The NMR data of the compounds obtained from this study was compared with the known pyrroles reported earlier.    Conclusion   Synthesis of N-substituted pyrrole derivatives were performed through ammonium chloride-catalyzed microwave-induced reaction. This method is environmentally friendly, simple and rapid. The high success with ammonium chloride will open up the possibility of performing many other reactions for the synthesis of other compounds of interest.   References  1. R. Baidoo, R. Danso, S. Mukherjee, D. Bandyopadhyay, and B. K. Banik,  Heterocyclic Letters, 1, 103, 2011. 2. (a) N. Iwasawa, K. Maeyama and M. Saitou, J. Am. Chem. Soc. 119, 1486, 1997; (b)  A. Katrizky, J. Jiang and P. J. Steel, J. Org. Chem. 59, 4551, 1994; (c) M. Periasamy, G. Srinivas, and P. J. Bharati, J. Org. Chem. 64, 4204, 1999; (d) P. Ruault, J. F. Pilard, B. Touaux, F. T. Boullet and J. Hamelin, Synlett, 935, 1994.   3. For an example of environmentally benign reaction, see: N. Srivastava and B. K.  Banik, J. Org. Chem. 68, 2109, 2003.   4. B. K. Banik, S. Samajdar and I. Banik, J. Org. Chem. 69, 213, 2004.   Received on February 6, 2017.            

MICROWAVE-INDUCED PAAL-KNORR REACTION WITH AMMONIUM CHLORIDE: SYNTHESIS OF PYRROLES

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MICROWAVE-INDUCED PAAL-KNORR REACTION WITH AMMONIUM CHLORIDE: SYNTHESIS OF PYRROLES

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