Synlett 2004(6): 1101-1103  
DOI: 10.1055/s-2004-822888
LETTER
© Georg Thieme Verlag Stuttgart · New York

Diastereoselective [4+2] Reactions of o-Quinone Methides with a Chiral Enol Ether: Asymmetric Synthesis of (+)-R-Mimosifoliol

Carolyn Selenski, Lupe H. Mejorado, Thomas R. R. Pettus*
Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, CA 93106-9510, USA
Fax: +1(805)8935690; e-Mail: pettus@chem.ucsb.edu;
Further Information

Publication History

Received 20 February 2004
Publication Date:
25 March 2004 (online)

Abstract

The first examples of enantioselective [4+2] cycloadditions of o-quinone methides (o-QMs) are reported. Their cycloaddition with trans-2-phenyl-1-cyclohexanol derived vinyl ether produces chiral benzopyrans. This procedure offers access to chiral aliphatic benzylic carbons and is applied to the synthesis of (+)-R-mimosifoliol.

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Compound 5: 1H NMR (400 MHz, CDCl3): δ 7.31-7.07 (m, 10 H), 6.67 (s, 1 H), 6.20 (s, 1 H), 4.46-4.43 (m, 1 H), 3.75-3.71 (m, 1 H), 3.66-3.65 (m, 1 H), 3.53 (s, 3 H), 2.47-2.46 (m, 1 H), 2.31-2.30 (m, 1 H), 1.90 (m, 6 H), 1.55 (s, 9 H), 1.51-1.27 (m, 3 H). 13C NMR (100 MHz, CDCl3): δ 151.8, 147.4, 145.4, 144.3, 144.2, 139.6, 128.8, 128.6, 128.3, 128.3, 126.8, 126.5, 123.3, 113.4, 111.7, 101.0, 84.4, 83.6, 56.6, 51.6, 41.4, 37.1, 34.9, 32.7, 27.8, 25.9, 25.5. Compound 6: 1H NMR (400 MHz, CDCl3): δ 7.31-7.19 (m, 5 H), 6.66 (s, 1 H), 6.59 (s, 1 H), 4.41-4.39 (m, 1 H), 3.77 (s, 3 H), 3.65-3.63 (m, 1 H), 2.61-2.49 (m, 2 H), 2.22-2.20 (m, 1 H), 1.91-1.56 (m, 6 H), 1.55 (s, 9 H), 1.54-1.22 (m, 6 H). 13C NMR (100 MHz, CDCl3): δ 151.8, 146.2, 145.5, 144.5, 139.2, 128.3, 128.2, 126,4, 126.6, 111.8, 111.6, 100.4, 83.8, 83.5, 56.8, 51.7, 35.4, 34.9, 33.0, 28.1, 27.8, 26.0, 25.5, 21.7. Compound 7: 1H NMR (400 MHz, CDCl3): δ 7.30-7.05 (m, 10 H), 6.68-6.51 (m, 2 H), 4.51-4.48 (m, 1 H), 3.72-3.66 (m, 2 H), 2.53-2.33 (m, 2 H), 1.91-1.62 (m, 3 H), 1.55 (s, 9 H), 1.49-1.28 (m, 3 H). 13C NMR (100 MHz, CDCl3): δ 154.3, 152.1, 150.5, 144.2, 130.0, 128.8, 128.7, 128.3, 128.3, 126.9, 123.5, 113.7, 110.2, 101.4, 84.5, 83.6, 51.6, 41.1, 36.8, 35.0, 32.7, 27.9, 26.0, 25.5. Compound 8: 1H NMR (400 MHz, CDCl3): δ 7.31-7.00 (m, 5 H), 6.89-6.59 (m, 2 H), 4.46-4.44 (m, 1 H), 3.70-3.64 (m, 1 H), 2.62-2.50 (m, 2 H), 2.23-2.21 (m, 1 H), 1.92-1.58 (m, 3 H), 1.55 (s, 9 H), 1.46-1.21 (m, 7 H). 13C NMR (100 MHz, CDCl3): δ 153.3, 152.2, 150.2, 144.5, 128.3, 128.2, 128.0, 126.5, 125.4, 113.6, 110.2, 100.7, 83.9, 51.7, 35.5, 34.9, 33.0, 29.9, 27.9, 27.8, 26.0, 25.5, 21.4. Compound 9: See ref. 13.

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Compound 3: 1H NMR (400 MHz, CDCl3): δ 10.06 (s, 1 H), 7.32 (s, 1 H), 6.69 (s, 1 H), 4.19 (t, J = 8.4 Hz, 2 H), 3.91 (s, 3 H), 1.59 (s, 9 H), 1.25 (t, J = 8.4 Hz, 2 H), 0.10 (s, 9 H). 13C NMR (100 MHz, CDCl3): δ 187.2, 154.5, 151.9, 148.3, 147.7, 120.6, 109.7, 106.6, 84.7, 67.3, 56.4, 27.9, 17.7, -1.3. IR (CH2Cl2): 2956, 2933, 2857, 1761, 1681, 1607, 1512.1, 1275 cm-1. LRMS (EI): m/z calcd for C18H28O6Si: 368; found: 368.

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Compound 9: [α]D 25 = +15 °C (c = 0.6, CHCl3). 1H NMR (400 MHz, CDCl3): δ 7.26-7.21 (m, 10 H), 6.37 (s, 1 H), 6.11 (s, 1 H), 4.47-4.45 (m, 1 H), 4.09-4.05 (t, J = 8.3 Hz, 2 H), 3.74-3.56 (m, 2 H), 3.54 (s, 3 H), 2.51-2.45 (m, 1 H), 2.35-2.23 (m, 1 H), 1.91-1.19 (m, 11 H), 0.09 (s, 9 H). 13C NMR (100 MHz, CDCl3): δ 148.2, 147.5, 144.9, 144.2, 143.7, 128.7, 128.4, 128.2, 127.4, 126.6, 126.4, 115.8, 112.7, 102.2, 101.1, 84.3, 66.3, 56.5, 51.6, 41.0, 37.4, 35.0, 32.7, 25.9, 25.4, 17.9, -1.3. IR (CH2Cl2): 2934, 2858, 1618, 1600, 1504, 1494, 1407, 1252 cm-1. HRMS (EI): m/z calcd for C33H42O4Si: 530.7697; found: 530.2835.

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Compound 13: 1H NMR (400 MHz, CDCl3): δ 7.34-7.20 (m, 5 H), 6.43 (s, 1 H), 6.26 (s, 1 H), 5.60-5.58 (m, 1 H), 4.27-4.23 (m, 1 H), 4.08 (t, J = 8.5 Hz, 2 H), 3.59 (s, 3 H), 2.29-2.23 (m, 1 H), 2.17-2.06 (m, 1 H), 1.23-1.21 (t, J = 8.5 Hz, 2 H), 0.07 (s, 2 H).

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Compound 14: [α]D 25 = +41 °C (c = 0.37, CHCl3). 1H NMR (400 MHz, CDCl3): δ 7.44-7.16 (m, 5 H), 6.68 (s, 1 H), 6.47 (s, 1 H), 4.53-4.49 (m, 1 H), 4.14-4.13 (m, 2 H), 3.74 (s, 3 H), 3.72 (s, 3 H), 2.90-2.87 (m, 2 H), 2.45-2.39 (m, 2 H), 1.24-1.21 (m, 2 H), 0.12 (s, 9 H). 13C NMR (100 MHz, CDCl3): δ 151.4, 147.5, 144.9, 128.5, 128.2, 126.2, 124.7, 113.2, 100.0, 76.7, 66.9, 61.3, 57.1, 57.0, 38.8, 37.9, 18.1, -1.2. IR (CH2Cl2): 3688, 3053, 2955, 2933, 1607, 1506, 1274 cm-1. HRMS (EI): m/z calcd for C22H32O4Si: 388.5726; found: 388.2083.