Synlett 2011(1): 124-128  
DOI: 10.1055/s-0030-1259083
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Cross Metathesis of N-Allylamines and α,β-Unsaturated Carbonyl Compounds: A One-Pot Synthesis of Substituted Pyrroles

Syed Shafia, Mariusz Kędziorekb, Karol Grela*a,b
a Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
b Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland
Fax: +48(22)3432109; e-Mail: klgrela@gmail.com;
Further Information

Publication History

Received 9 October 2010
Publication Date:
07 December 2010 (online)

Abstract

A tandem reaction involving cross metathesis followed by concomitant cyclisation has been developed for the synthesis of substituted pyrroles. Various protected electron-deficient N-allylamines reacted with α,β-unsaturated carbonyl compounds in the presence of Lewis acids under the cross metathesis conditions using selected Ru olefin metathesis catalysts in order to form pyrroles.

    References and Notes

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  • 6a During the preparation of this manuscript, a related two-step approach to substituted pyrroles via olefin cross meta-thesis and subsequent acid-catalysed cyclisation was published by Donohoe et al., presenting also an excellent example of the application of this methodology towards the synthesis of the tetrasubstituted pyrrole subunit of Atorvastatin, see: Donohoe TJ. Race NJ. Bower JF. Callens CKA. Org. Lett.  2010,  12:  4094 
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General procedure: All reactions were performed using Schlenk techniques under an argon atmosphere. Solvents were degassed (using Freeze-Pump-Thaw techniques) before use. Metathesis catalysts and all commercially available chemicals were used as received. See the Supporting Information for full experimental procedures
and product characterisation data

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Pyrrol-1-yl(1H-pyrrol-2-yl)methanone (10z); Typical procedure: In a dry Schlenk tube, substrate 10x (100 mg, 0.66 mmol), B(OPh)3 (19 mg, 10 mol%) and crotonaldehyde (233 mg, 3.3 mmol) were dissolved in anhydrous toluene (5 mL) and stirred for 5 min under an argon atmosphere. The first portion of the catalyst Hov-II (10.5 mg, 2.5 mol%) was added as a solid. The reaction mixture was heated to reflux and, after 15 min, the second portion of the catalyst was added (10.5 mg, 2.5 mol%) under an argon atmosphere and heating was continued until the reaction was complete according to TLC. The reaction mixture was cooled and the solvent was evaporated. The crude product was purified by flash chromatography (c-hexane-EtOAc, 19:1) to yield 10z as a colourless solid (64.01 mg, 60%); Mp 56-58 ˚C. ¹H NMR (500 MHz, CDCl3): δ = 6.36 (t, J = 2.30, 2.29 Hz, 2 H), 6.37-6.38 (m, 1 H), 6.98-6.99 (m, 1 H), 7.11-7.14 (m, 1 H), 7.52 (t, J = 2.29, 2.30 Hz, 2 H), 9.86 (br, 1 H). ¹³C NMR (125 MHz, CDCl3): δ = 111.19, 112.71, 117.61, 120.65, 123.92, 124.95, 159.01. IR (KBr): 3306, 3158, 2958, 2924, 1645, 1545, 1467, 1456, 1424, 1412, 1389, 1345, 1277, 1244, 1138, 1108, 1099, 1074, 1042, 990, 941, 887, 864, 842, 766, 751, 728, 630, 604 cm. MS (EI): m/z (%) = 160 (91) [M]+ ˙ , 94 (100), 67 (48), 66 (28). HRMS (EI): m/z calcd for C9H8N2O: 160.06366; found: 160.06381. Anal. Calcd for C9H8N2O: C, 67.49; H, 5.03; N, 17.49. Found: C, 67.44; H, 4.88; N, 17.57.

13

This work was presented for the first time during the European Congress of Young Chemists ‘YoungChem 2009’, Warsaw, Poland, October 14-18, 2009: ‘Ru catalyzed imine formation followed by RCM of N- allylamines: A tandem reaction towards the synthesis of substituted pyrroles’; S. Shafi, oral presentation