References and Notes
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1a
Kimura M.
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Tamaki T.
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1b
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1c
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1d
Restorp P.
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2a
Olah GA.
Krishnamurti R.
Prakash SGK. In Comprehensive Organic Synthesis
Vol. 3:
Trost BM.
Fleming I.
Pergamon Press;
Oxford:
1991.
p.293
For recent examples, see:
2b
Bertolini F.
Crotti P.
Macchia F.
Pineschi M.
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2006,
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61
2c
Prakash SGK.
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3 Vinyloxiranes have been used in an intramolecular process to control a 7-endo-selective Friedel-Crafts-type cyclization. See: Nagumo S.
Miyoshi I.
Akita H.
Kawahara N.
Tetrahedron Lett.
2002,
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2223
4a
Taylor SK.
Clark DL.
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Barnell KK.
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1983,
48:
592
4b The drastic reaction conditions used in this work, allowed direct ring opening of the oxirane ring by the Lewis acid promoter and caused the resulting alcohols to undergo a further Friedel-Crafts alkylation to give diarylated products.
5 For Friedel-Crafts reactions of a sulfonyl-substituted vinylic epoxide with various aromatics promoted by BF3·Et2O, see: Brandänge S.
Bäckvall J.-E.
Leijonmarck H.
J. Chem. Soc., Perkin Trans. 1
2001,
2051
6 For the reactions of methyl 4,5-epoxypentenoate with aryl ethers, see: Ono M.
Tanikawa S.
Suzuki K.
Akita H.
Tetrahedron
2004,
60:
10187 ; and references cited therein
7
Pineschi M.
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8
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Richard JP.
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For the use of indium salts in Friedel-Crafts-type reactions of heteroarenes with epoxides, see:
9a
Yadav JS.
Reddy BVS.
Parimala G.
Synlett
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9b
Bandini M.
Cozzi PG.
Melchiorre P.
Umani-Ronchi A.
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For the synthesis of tetrahydrobenzofurans, see:
10a
Hosokawa T.
Miyagi S.
Murahashi S.-I.
Sonoda A.
J. Org. Chem.
1978,
43:
2752
10b
Guzzo PR.
Buckle RN.
Chou M.
Dinn SR.
Flaugh ME.
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10c
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Inaba T.
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10d
Crich D.
Sannigrahi M.
Tetrahedron
2002,
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For the obtainment of hexahydrodibenzofurans, see:
10e
Liu Q.
Han B.
Zhang W.
Yang L.
Liu Z.-L.
Yu W.
Synlett
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10f
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10g
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11a
Clive DLJ.
Daigneault S.
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12
Aristoff PA.
Harrison AW.
Huber AM.
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1984,
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3955
13 Aryl borates 1a,b were prepared from the corresponding commercially available phenols with BH3·SMe2,14 and were used immediately after their preparation.
Typical Procedure for the Preparation of Hydroxy-phenols (Entry 7, Table 1): Under an argon atmosphere, a solution of aryl borate 1b (705 mg, 1.5 mmol) in CH2Cl2 (1.0 mL) was added at -78 °C to a stirred solution of vinyloxirane 2a (96 mg, 1.0 mmol) in CH2Cl2 (0.5 mL). The mixture was allowed to react for 18 h at -78 °C, then quenched with brine (2.0 mL) and diluted with Et2O or CH2Cl2 (20 mL). Evaporation of the dried (MgSO4) organic solution afforded a crude reaction mixture which was purified by silica gel column chromatography eluting with hexanes-EtOAc (7:3), to give pure 2-[(1R*,6S*)-6-hydroxycyclohexen-2-yl]-3,5-dimethoxyphenol (4ab; 162 mg, 65%), as a light yellow oil; TLC (hexanes-EtOAc, 1:1): R
f
0.36. 1H NMR (250 MHz, CDCl3): δ = 1.70-1.90 (m, 1 H), 2.05-2.18 (m, 1 H), 2.30-2.43 (m, 2 H), 2.50-2.67 (br s, 1 H, CHOH), 3.82 (s, 3 H), 3.83 (s, 3 H), 3.95-4.10 (m, 2 H), 5.67-5.83 (m, 2 H), 5.93-6.05 (m, 1 H), 6.10-6.25 (m, 1 H), 6.50-6.70 (br s, 1 H, ArOH). 13C NMR (62.5 MHz, CDCl3): δ = 24.6, 30.7, 40.6, 55.1, 55.6, 71.2, 91.5, 94.5, 106.1, 107.7, 128.8, 156.9, 159.2, 159.9.
2-[(1
R
*,6
S
*)-6-Hydroxycyclohexen-2-yl]-3,5-dimethyl-phenol (4aa): yield: 40%; solid; mp 119-122 °C; TLC (hexanes-EtOAc, 7:3): R
f
0.20. 1H NMR (200 MHz, MeOD): δ = 1.56-1.86 (m, 2 H), 1.93-2.12 (m, 2 H), 2.17 (s, 3 H), 2.27 (s, 3 H), 3.62-3.89 (m, 1 H), 4.12-4.33 (m, 1 H), 5.45 (d, J = 9.8 Hz, 1 H), 5.56-5.71 (m, 1 H), 6.46 (s, 2 H). 13C NMR (50 MHz, MeOD): δ = 21.0, 21.2, 26.4, 33.4, 45.3, 71.1, 115.3, 124.2, 125.4, 126.0, 131.7, 137.6, 139.5, 157.1.
2-(1-Hydroxybut-3-en-2-yl)-3,5-dimethylphenol (6aa): yield: 54%; colorless oil; TLC (hexanes-EtOAc, 6:4): R
f
0.31. 1H NMR (200 MHz, CDCl3): δ = 2.24 (s, 3 H), 2.28 (s, 3 H), 3.63 (br s, 1 H), 3.81-4.19 (m, 3 H), 5.04-5.24 (m, 2 H), 6.22 (ddd, J
1 = 16.6 Hz, J
2 = 10.4 Hz, J
3 = 5.3 Hz, 1 H), 6.58 (s, 1 H), 6.60 (s, 1 H), 8.26 (br s, 1 H). 13C NMR (50 MHz, CDCl3): δ = 20.7, 44.8, 65.1, 116.1, 116.5, 122.4, 123.6, 136.0, 137.6, 154.7.
2-(1-Hydroxybut-3-en-2-yl)-3,5-dimethoxyphenol (6ab): yield: 75%; colorless oil; TLC (hexanes-EtOAc, 8:2): R
f
0.13. 1H NMR (200 MHz, CDCl3): δ = 3.73 (s, 6 H), 3.89 (dd, J
1 = 10.2 Hz, J
1 = 3.2 Hz, 1 H), 4.02-4.15 (m, 1 H), 4.16-4.28 (m, 1 H), 5.00-5.19 (m, 2 H), 6.03-6.12 (m, 2 H), 6.13-6.23 (m, 1 H). 13C NMR (500 MHz, CDCl3): δ = 40.0, 54.5, 55.7, 65.7, 91.2, 94.7, 108.0, 116.1, 136.7, 156.6, 158.6, 159.8.
(
E
)-2-(6-Hydroxynon-4-en-3-yl)-3,5-dimethoxyphenol (6bb): yield: 65%; colorless oil; TLC (hexanes-EtOAc, 7:3): R
f
0.27. 1H NMR (250 MHz, CDCl3): δ = 0.79 (t, 3 H), 0.86 (t, J = 7.1 Hz, 3 H), 1.19-1.52 (m, 4 H), 1.62-1.82 (m, 2 H), 2.20 (br s, 1 H, CHOH), 3.69 (s, 3 H), 3.71 (s, 3 H), 3.74-3.89 (m, 1 H), 4.06-4.13 (m, 1 H), 5.55 (dd, J
1 = 16.3 Hz, J
2 = 6.7 Hz, 1 H), 5.98-6.18 (m, 3 H). 13C NMR (62.5 MHz, CDCl3): δ = 12.3, 13.9, 18.61, 25.49, 38.27, 39.31, 55.1, 55.6, 72.7, 91.4, 94.4, 110.2, 132.6, 134.4, 158.8, 159.1.
(4
S*
,5
S*
,
E
)-Ethyl 5-Hydroxy-4-(2-hydroxy-4,6-dimethylphenyl)oct-2-enoate (6cb): yield: 40%; colorless oil; TLC (hexanes-EtOAc, 7:3): R
f
0.19. 1H NMR (200 MHz, CDCl3): δ = 0. 93 (t, J = 7.1 Hz, 3 H), 1.25 (t, J = 5.7 Hz, 3 H), 1.33-1.74 (m, 4 H), 3.52 (br s, 1 H, CHOH), 3.74 (s, 6 H), 3.95-4.30 (m, 4 H), 5.78 (d, J = 15.8 Hz, 1 H), 6.04 (s, 1 H), 6.11 (s, 1 H), 7.38 (dd, J
1 = 15.8 Hz, J
2 = 7.2 Hz, 1 H), 9.22 (br s, 1 H). 13C NMR (50 MHz, CDCl3): δ = 13.7, 14.1, 19.0, 38.1, 42.3, 55.1, 55.7, 60.3, 75.4, 91.0, 94.8, 108.0, 123.1, 145.2, 156.8, 158.2, 160.1, 167.0.
(1
S*
,2
R*
)-2-(2-Hydroxy-4,6-dimethoxyphenyl)cyclo-hept-3-enol (4bb): yield: 58% [obtained as an inseparable mixture with 7% of the corresponding (1S*,2S*)-stereoisomer]; TLC (hexanes-EtOAc, 7:3): R
f
0.16. 1H NMR (200 MHz, CDCl3): δ = 1.40-2.42 (m, 6 H), 3.70 (s, 3 H), 3.74 (s, 3 H), 3.93-4.17 (m, 2 H), 5.50-5.61 (m, 1 H), 5.77-5.95 (m, 1 H), 6.01 (d, J = 2.3 Hz, 1 H), (6.06 d, J = 2.3 Hz, 1 H), 6.94-7.03 (br s, 1 H, ArOH). 13C NMR (50 MHz, CDCl3): δ = 24.7, 27.8, 39.8, 43.3, 55.1, 55.6, 71.1, 91.2, 94.4, 109.0, 132.1, 133.0, 156.3, 159.5, 159.7.
Typical Procedure for the Preparation of 2,3-Dihydro-benzofuranes via Mitsunobu Cyclodehydration (Scheme 2): Triphenylphosphine (262.3 mg, 1.0 mmol) and diethyl-azodicarboxylate (118 µL, 0.75 mmol) were added to a stirred solution of hydroxyphenol 4ab (125 mg, 0.5 mmol) in anhyd THF (2.0 mL) under argon. The reaction was followed by TLC up to complete consumption of the starting hydroxyphenol and the solvent was removed in vacuo. The crude reaction mixture was purified by silica gel column chromatography to give pure (4aR*,9bR*)-7,9-dimethoxy-3,4,4a,9b-tetrahydrodibenzo[b,d]furan (7ab; 94 mg, 81%) as a light yellow oil. 1H NMR (200 MHz, CDCl3): δ = 1.75-2.31 (m, 4 H), 3.75 (s, 3 H), 3.79 (s, 3 H), 3.81-3.88 (m, 1 H), 4.93-5.05 (m, 1 H), 5.73-5.95 (m, 2 H), 6.00 (d, J = 2.0 Hz, 1 H), 6.05 (d, J = 2.0 Hz, 1 H). 13C NMR (50 MHz, CDCl3): δ = 19.2, 25.1, 39.0, 55.1, 55.4, 82.3, 88.7, 91.0, 110.1, 126.0, 126.7, 156.7, 161.1, 161.5.
(4a
R
*,9b
R
*)-7,9-Dimethyl-3,4,4a,9b-tetrahydro-dibenzo[
b
,
d
]furan (7aa): yield: 83%; colorless oil; TLC (hexanes-Et2O, 9:1): R
f
0.51. 1H NMR (200 MHz, CDCl3): δ = 1.75-2.12 (m, 2 H), 2.19-2.30 (m, 2 H), 2.27 (s, 3 H), 2.30 (s, 3 H), 3.77 (br d, J = 6.9 Hz, 1 H), 4.94-5.00 (m, 1 H), 5.68-5.95 (m, 2 H), 6.48 (s, 1 H), 6.50 (s, 1 H). 13C NMR (50 MHz, CDCl3): δ = 18.3, 19.0, 21.4, 24.9, 40.1, 81.3, 108.0, 122.6, 125.1, 126.9, 127.8, 134.0, 138.2.
(5a
R
*,10a
R
*)-1,3-Dimethoxy-6,7,8,10a-tetrahydro-5a
H
-benzo[
d
]cyclohepta[
b
]furan (7bb): yield: 80% (obtained as an inseparable mixture with 10% of the corresponding trans stereoisomer); light yellow oil; TLC (hexanes-EtOAc, 9:1): R
f
0.38. 1H NMR (200 MHz, CDCl3): δ = 1.55-1.75 (m, 2 H), 1.92-2.07 (m, 2 H), 2.09-2.22 (m, 2 H), 3.76 (s, 3 H), 3.80 (s, 3 H), 4.25 (d, J = 9.8 Hz, 1 H), 4.88 (ddd, J
1 = 4.5 Hz, J
2 = 9.8 Hz, 1 H), 5.62-5.68 (m, 2 H), 6.00-6.05 (m, 2 H). 13C NMR (50 MHz, CDCl3): δ = 19.4, 26.7, 28.7, 42.4, 55.3, 55.5, 85.5, 88.1, 91.1, 127.6, 129.7, 159.0, 160.3, 160.7.
(5a
S
*,11a
S
*,
Z
)-1,3-Dimethoxy-5a,6,7,8,11a-hexa-hydrobenzo[
b
]cycloocta[
d
]furan (7cb): yield: (70%); light yellow oil; TLC (hexanes-EtOAc, 9:1): R
f
0.45. 1H NMR (200 MHz, CDCl3): δ = 0.95-2.25 (m, 8 H), 3.72 (s, 3 H), 3.76 (s, 3 H), 4.10-4.26 (m, 1 H), 4.50-4.67 (m, 1 H), 5.11 (dd, J
1 = 10.6 Hz, J
2 = 7.0 Hz, 1 H), 5.68-5.88 (m, 1 H), 6.00 (s, 2 H). 13C NMR (50 MHz, CDCl3): δ = 26.6, 26.7, 28.2, 29.2, 40.4, 55.5 (2 × C), 88.3, 91.3, 91.5, 11.8, 130.5, 133.3, 156.7, 160.5, 161.6.
14
Brown CA.
Krishnamurthy S.
J. Org. Chem.
1978,
43:
2731