Synlett 2017; 28(02): 239-244
DOI: 10.1055/s-0036-1588622
letter
© Georg Thieme Verlag Stuttgart · New York

Lewis Acid Mediated [3+2] Coupling of Masked Benzoquinones with Styrenes: Facile Synthesis of 2,3-Dihydrobenzofurans

Shivangi Sharma
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, Uttarakhand, India   eMail: rkpedfcy@iitr.ac.in   eMail: ramakpeddinti@gmail.com
,
Santosh Kumar Reddy Parumala
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, Uttarakhand, India   eMail: rkpedfcy@iitr.ac.in   eMail: ramakpeddinti@gmail.com
,
Rama Krishna Peddinti*
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, Uttarakhand, India   eMail: rkpedfcy@iitr.ac.in   eMail: ramakpeddinti@gmail.com
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Publikationsverlauf

Received: 22. Juli 2016

Accepted after revision: 20. September 2016

Publikationsdatum:
11. Oktober 2016 (online)


Abstract

We have developed an efficient, simple, mild, and rapid method for the construction of dihydrobenzofuran derivatives by the [3+2] coupling of masked o-benzoquinones with styrene derivatives triggered by boron trifluoride diethyl etherate. This new [3+2] coupling protocol proceeds smoothly to afford dihydrobenzofuran derivatives in good to high yields within one minute. The method was extended to cycloaddition of p-benzoquinone monoketal with styrenes.

Supporting Information

 
  • References and Notes

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  • 13 Parumala SK. R, Surasani SR, Peddinti RK. New J. Chem. 2014; 38: 5268
  • 15 Parumala SK. R, Peddinti RK. Org. Lett. 2013; 15: 3546
  • 16 Gao S.-Y, Ko S, Lin Y.-L, Peddinti RK, Liao C.-C. Tetrahedron 2001; 57: 297
  • 17 2,3-Dihydrobenzofuran Derivatives 4; General Procedure PhI(OAc)2 (0.177 g, 0.55 mmol, 1.1 equiv) was added to a solution of the appropriate guaiacol derivative 1 (0.5 mmol) in MeOH (5 mL), and the mixture was stirred for 5 min at r.t. After generation of the o-benzoquinone monoketal 2, as indicated by a yellow color of the solution, the MeOH was removed under reduced pressure and the residue was dissolved in CH2Cl2. The solution was cooled to –30 °C and the appropriate alkene (1 mmol) and BF3·OEt2 (1 mmol) were added sequentially. When the reaction was complete (TLC), it was quenched with sat. aq NaHCO3 and the mixture was extracted with CH2Cl2 (2 × 15 mL). The combined organic phases were dried (Na2SO4), filtered, and evaporated to dryness. The crude product was purified by column chromatography (silica gel, 1–2% EtOAc–hexanes). 5-Bromo-7-methoxy-2-phenyl-2,3-dihydrobenzofuran (4aa) Viscous yellow liquid; yield: 0.124 g (82%). IR (KBr): 2928, 2851, 1615, 1484, 1293, 1270, 1197, 1094, 763, 699 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.41–7.29 (m, 5 H), 6.95–6.94 (m, 1 H), 6.91–6.90 (m, 1 H), 5.80 (t, J = 9.0 Hz, 1 H), 3.87 (s, 3 H), 3.61 (dd, J = 9.5, 15.5 Hz, 1 H), 3.23 (dd, J = 8.5, 16.0 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 147.1 (C), 144.7 (C), 140.9 (C), 129.1 (C), 128.5 (CH), 128.1 (CH), 125.8 (CH), 119.8 (CH), 114.6 (CH), 112.3 (C), 85.1 (CH), 56.1 (OCH3), 38.5 (CH2). 5-Bromo-2-(4-isopropylphenyl)-7-methoxy-2,3-dihydrobenzofuran (4ah) Viscous colorless liquid; yield: 0.140 g (81%). IR (KBr): 2959, 2931, 1615, 1483, 1293, 1195, 1095, 946, 831, 776 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.30 (d, J = 8.0 Hz, 2 H), 7.20 (d, J = 7.5 Hz, 2 H), 6.92 (s, 1 H), 6.88 (s, 1 H), 5.75 (t, J = 8.5 Hz, 1 H), 3.83 (s, 3 H), 3.56 (dd, J = 9.0, 15.5 Hz, 1 H), 3.23 (dd, J = 8.5, 16.0 Hz, 1 H), 2.89 (quint, J = 6.5 Hz, 1 H), 1.23 (s, 3 H), 1.22 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 149.0 (C), 147.2 (C), 144.8 (C), 138.3 (C), 129.3 (C), 126.6 (CH), 126.1 (CH), 119.9 (CH), 114.8 (CH), 112.2 (C), 85.2 (CH), 56.2 (OCH3), 38.3 (CH2), 33.8 (CH3), 23.9 (CH3). 2-(4-Bromophenyl)-5-chloro-7-methoxy-2,3-dihydrobenzofuran (4bc) Viscous colorless liquid; yield: 0.135 g (80%). IR (KBr): 2931, 2840, 1617, 1485, 1297, 1196, 1097, 1072, 946, 826, 790 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.38 (d, J = 8.0 Hz, 2 H), 7.17 (d, J = 7.5 Hz, 2 H), 6.69 (s, 1 H), 6.67 (s, 1 H), 5.66 (t, J = 8.5 Hz, 1 H), 3.77 (s, 3 H), 3.50 (dd, J = 10.0, 16.0 Hz, 1 H), 3.06 (dd, J = 8.5, 15.5 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 146.4 (C), 144.4 (C), 140.1 (C), 131.7 (CH), 128.1 (C), 127.5 (CH), 125.6 (C), 122.0 (C), 116.9 (CH), 111.9 (CH), 84.3 (CH), 56.1 (OCH3), 38.5 (CH2). 5-Chloro-7-methoxy-2-methyl-2-phenyl-2,3-dihydrobenzofuran (4bg) Viscous colorless liquid; yield: 0.092 g (67%). IR (KBr): 2981, 2925, 1616, 1487, 1444, 1301, 1233, 1099, 838, 764 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.46 (d, J = 8.0 Hz, 2 H), 7.34 (t, J = 7.5 Hz, 2 H), 7.24–7.28 (m, 1 H), 6.76 (s, 1 H), 6.74 (s, 1 H), 3.91 (s, 3 H), 3.40 (q, J = 15.5 Hz, 2 H), 1.81 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 146.0 (C), 145.9 (C), 144.6 (C), 128.4 (CH), 127.2 (CH), 125.2 (C), 124.4 (CH), 117.1 (CH), 111.9 (CH), 90.5 (C), 56.2 (OCH3), 45.0 (CH2), 29.2 (CH3). 5-Iodo-7-methoxy-2-methyl-2-phenyl-2,3-dihydrobenzofuran (4cg) Viscous colorless liquid; yield: 0.126 g (69%). IR (KBr): 2966, 1609, 1482, 1294, 1141, 1093, 832, 761 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.47 (d, J = 7.5 Hz, 2 H), 7.36 (t, J = 7.5 Hz, 2 H), 7.29–7.26 (m, 1 H), 7.09 (s, 1 H), 7.07 (s, 1 H), 3.92 (s, 3 H), 3.42 (q, J = 15.5 Hz, 2 H), 1.83 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 147.2 (C), 145.9 (C), 145.3 (C), 129.7 (C), 128.3 (CH), 127.2 (CH), 126.1 (CH), 124.4 (CH), 120.2 (CH), 90.5 (C), 81.4 (C), 56.2 (OCH3), 44.7 (CH2), 29.1 (CH3). trans-5-Iodo-7-methoxy-3-methyl-2-phenyl-2,3-dihydrobenzofuran (4ci) Viscous colorless liquid; yield: 0.130 g (71%). IR (KBr): 2960, 1610, 1479, 1279, 1195, 1078, 965, 833 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.42–7.32 (m, 5 H), 7.08 (s, 2 H), 5.22 (d, J = 9.0 Hz, 1 H), 3.51 (s, 3 H), 3.48 (quint, J = 7.0 Hz, 1 H), 1.41 (d, J = 6.5 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 147.5 (C), 145.1 (C), 139.9 (C), 135.2 (C), 128.6 (CH), 128.4 (CH), 126.2 (CH), 125.0 (CH), 120.5 (CH), 93.3 (CH), 81.9 (C), 56.2 (OCH3), 45.7 (CH), 18.0 (CH3).
  • 18 For the stereochemistry of similar compounds, see ref. 6b and: Juhász L, Szilágyi L, Antus S, Visy J, Zsila F, Simonyi M. Tetrahedron 2002; 58: 4261