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

Syed Shafi; Mariusz Kędziorek; Karol Grela

doi:10.1055/s-0030-1259083

LETTER

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

Syed Shafi^a, Mariusz Kędziorek^b, 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;

Abstract

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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.

Key words

ruthenium - catalysis - olefin metathesis - Lewis acids - heterocycles

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References

References and Notes

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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

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^-¹. 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.

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

Supplementary Material

Supporting Information