Bu₄N[AuCl₄]-Catalyzed Synthesis of Highly Substituted Furans from 2-(1-Alkynyl)-2-alken-1-ones in Ionic Liquids: An Air-Stable and Recyclable Catalytic System

Abstract

The cyclization of 2-(1-alkynyl)-2-alken-1-ones proceeded smoothly in the presence of various nucleophiles with a ­catalytic amount of Bu₄N[AuCl₄] in [bmim]BF₄, leading to the formation of highly substituted furans. This system is air-stable and ­recyclable. The catalyst is inexpensive and readily available.

gold-catalyzed - cyclization reaction - ionic liquids - furans - recyclable

References and Notes

1 Maier M. Organic Synthesis Highlights II   Waldmann H. VCH; Weinheim: 1995.  p.231 

2 Donnelly DMX. Meegan MJ. Comprehensive Heterocyclic Chemistry   Vol. 4:  Katritzky AR. Rees CW. Pergamon; New York: 1984.  p.657 

Recent reviews:

3a Hou XL. Yang Z. Wong HNC. Progress in Heterocyclic Chemistry   Vol. 14:  Gribble GW. Gilchrist TL. Pergamon Press; Oxford: 2002.  p.139-179  

3b Hou XL. Chueng HY. Hong TY. Kwan PL. Lo TH. Tong SY. Wong HNC. Tetrahedron  1998,  54:  1955 

3c Cacchi S. J. Organomet. Chem.  1999,  576:  42 

3d Keay BA. Chem. Soc. Rev.  1999,  28:  209 

3e Lipshutz BH. Chem. Rev.  1986,  86:  795 

4a Sheng H. Lin S. Huang Y. Tetrahedron Lett.  1986,  27:  4893 

4b Fukuda Y. Shiragami H. Utimoto K. Nozaki H. J. Org. Chem.  1991,  56:  5816 

4c Kel’in AV. Gevorgyan V. J. Org. Chem.  2002,  67:  95 

4d Ma S. Zhang J. Chem. Commun.  2000,  117 

4e Ma S. Zhang J. Lu L. Chem. Eur. J.  2003,  9:  2447 

4f Hashmi ASK. Schwarz L. Choi J.-H. Frost TM. Angew. Chem. Int. Ed.  2000,  39:  2285 

4g Marshall JA. Wang X.-J. J. Org. Chem.  1991,  56:  960 

4h Marshall JA. Wang X.-J. J. Org. Chem.  1992,  57:  3387 

4i Marshall JA. Bartley GS. J. Org. Chem.  1994,  59:  7169 

4j Arcadi A. Cacchi S. Larock RC. Marinelli F. Tetrahedron Lett.  1993,  34:  2813 

4k For a recent review, see: Brown RCD. Angew. Chem. Int. Ed.  2005,  44:  850 

5a Lo CY. Guo H. Lian JJ. Shen FM. Liu RS. J. Org. Chem.  2002,  67:  3930 

5b Marshall JA. DuBay WJ. J. Am. Chem. Soc.  1992,  114:  1450 

5c Hashmi ASK. Sinha P. Adv. Synth. Catal.  2004,  346:  432 

6a Gabriele B. Salerno G. Lauria E. J. Org. Chem.  1999,  64:  7687 

6b Seiller B. Bruneau C. Dixneuf PH. J. Chem. Soc., Chem. Commun.  1994,  493 

6c Liu Y. Song F. Song Z. Liu M. Yan B. Org. Lett.  2005,  7:  5409 

7 Bew SP. Knight DW. Chem. Commun.  1996,  1007 

8a Yao T. Zhang X. Larock RC. J. Am. Chem. Soc.  2004,  126:  11164 

8b Suhre MH. Reif M. Kirsch SF. Org. Lett.  2005,  7:  3925 

8c For a review of gold catalysis, see: Hashmi ASK. Gold Bull.  2004,  37:  51 

9 Patil NT. Wu H. Yamamoto Y. J. Org. Chem.  2005,  70:  4531 

For the synthesis of furans by the electrophilic cyclization of the same substrate, see:

10a Yao T. Zhang X. Larock RC. J. Org. Chem.  2005,  70:  7679 

10b Liu Y. Zhou S. Org. Lett.  2005,  7:  4609 

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Representative Procedure.
To the appropriate 2-(1-alkynyl)-2-alken-1-one (0.2 mmol) and nucleophile (1.5 equiv) in [bmim]BF₄ (1 mL) was added Bu₄N[AuCl₄] (1 mol%). The mixture was stirred at r.t. for 3 h unless otherwise specified. The mixture was extracted with Et₂O (2 ¥ 5 mL). The isolated ether layer was concentrated in vacuo and the residue was purified by flash chromatography on silica gel.

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Recycling Procedure.
To the 2-phenylethynyl-2-cyclohexen-1-one (1.0 mmol) and MeOH (1.5 equiv) in [bmim]BF₄ (3 mL) was added Bu₄N[AuCl₄] (1 mol%). The mixture was stirred at r.t. for 3 h. The product was extracted from the reaction mixture by addition of Et₂O (2 ¥ 20 mL). The ether layer was separated. The ionic liquid layer containing Au catalyst was pumped for several minutes and reused for the next reaction.

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Spectral Data of the Representative Product 2a.
¹H NMR (300 MHz, CDCl₃): δ = 1.79-1.93 (m, 2 H), 1.94-2.05 (m, 2 H), 2.59-2.75 (m, 2 H), 3.43 (s, 3 H), 4.28 (t, J = 3.9 Hz, 1 H), 6.64 (s, 1 H), 7.18-7.23 (m, 1 H), 7.31-7.36 (m, 2 H), 7.60-7.63 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 18.8, 23.2, 28.3, 56.1, 72.3, 105.3, 119.9, 123.3, 126.8, 128.5, 131.1, 152.2, 152.8.