Efficient Access to Fused Ring Compounds via Dearomatization/Ring-Closing Metathesis

E. Peter Kündig; Alejandro Bellido; Krishna P. Kaliappan; Andrew R. Pape; Sylvie Radix

doi:10.1055/s-2003-43330

LETTER

Efficient Access to Fused Ring Compounds via Dearomatization/Ring-Closing Metathesis

E. Peter Kündig*, Alejandro Bellido, Krishna P. Kaliappan, Andrew R. Pape, Sylvie Radix
Department of Organic Chemistry, University of Geneva, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland
Fax: +41(22)3793215; e-Mail: Peter.Kundig@chiorg.unige.ch;

Abstract

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Abstract

The complex (p-methoxyphenyl oxazoline)Cr(CO)₃ is converted in two steps into a cis-fused [6,8] ring system containing a cycohexadiene ring unit, a cyclooctenone ring and a quaternary carbon at the ring junction. The key steps involve a diastereoselective addition of three C-substituents across an arene double bond, followed by an allylation and ring closing metathesis step. cis-Fused [6,7], [6,6], and [6,5] ring systems are also accessible via this methodology.

Key words

dearomatization - arene chromium complex - phenyl oxazoline - ring closing closing metathesis

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References

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Data for rac-2: IR (CH₂Cl₂): 2971, 2934, 1703, 1606, 1572, 1461, 1265, 1247, 1207, 1001, 916 cm^-1. ¹H NMR (200 MHz, C₆D₆): δ = 6.94 (d, J = 6.7 Hz, 1 H), 6.22-5.98 (m, 1 H), 5.87-5.66 (m, 1 H), 5.09-4.88 (m, 4 H), 4.74 (d, J = 6.7 Hz, 1 H), 3.68 (d, J = 7.9 Hz, 2 H), 3.43 (t, J = 7.1 Hz, 1 H), 3.02 (s, 3 H), 2.58-2.29 (m, 6 H), 1.41 (s, 3 H), 1.20 (s, 3 H), 1.15 (s, 3 H). ¹³C NMR (50 MHz, C₆D₆): δ = 209.0, 166.1, 162.6, 138.2, 137.0, 119.9, 115.8, 115.2, 93.8, 78.7, 67.7, 56.9, 54.9, 44.9, 42.1, 36.0, 28.7, 28.4, 21.9. HRMS (EI) on (M⁺) found: 343.2152, C₂₁H₂₉NO₃ requires 343.2147.

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Data for rac-4: IR (CH₂Cl₂): 2969, 2934, 1703, 1606, 1573, 1455, 1378, 1248, 1204, 1045, 1007, 708 cm^-1. ¹H NMR (200 MHz, C₆D₆): δ = 6.91 (d, J = 6.7 Hz, 1 H), 5.88-5.71 (m, 1 H), 5.58-5.45 (m, 1 H), 4.75 (d, J = 6.7 Hz, 1 H), 3.69 (d, J = 7.9 Hz, 1 H), 3.65 (d, J = 7.9 Hz, 1 H), 3.15-2.98 (m, 3 H), 2.95 (s, 3 H), 2.72-1.95 (m, 4 H), 1.46 (s, 3 H), 1.17 (s, 3 H), 1.14 (s, 3 H). ¹³C NMR (50 MHz, C₆D₆): δ = 210.2, 165.1, 161.6, 130.8, 126.1, 121.9, 93.1, 78.6, 67.7, 55.6, 54.9, 44.9, 41.2, 29.2, 28.7, 28.5, 26.4, 21.1. HRMS (EI) on (M⁺) found: 315.1814, C₁₉H₂₅O₃N requires 315.1834.

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12

Data for rac-7: IR (CH₂Cl₂): 2968, 2953, 1712, 1607, 1577, 1463, 1257, 1204, 1084, 1008 cm^-1. ¹H NMR (200 MHz, C₆D₆): δ = 6.94 (d, J = 6.7 Hz, 1 H), 6.18-6.08 (m, 1 H), 5.75-5.61 (m, 1 H), 4.65 (d, J = 6.7 Hz, 1 H), 3.85 (d, J = 4.7 Hz, 1 H), 3.67 (d, J = 1.3 Hz, 2 H), 2.90 (s, 3 H), 2.75-2.38 (m, 3 H), 1.67-1.48 (m, 1 H), 1.53 (s, 3 H), 1.16 (s, 3 H), 1.13 (s, 3 H). ¹³C NMR (50 MHz, C₆D₆): δ = 207.7, 164.9, 161.7, 132.9, 127.1, 120.6, 92.6, 78.7, 67.7, 55.1, 54.7, 47.0, 45.4, 28.6, 28.5, 21.9, 21.7. HRMS (EI) on (M⁺) found: 301.1677, C₁₈H₂₃NO₃ requires 301.1670. The oxazoline group in 7 was cleaved to give the corresponding aldehyde in a one-pot reaction [i) MeI, reflux; ii) NaBH₄, MeOH:CH₂Cl₂:THF, 0 °C; iii) p-TsOH, H₂O:THF] in 61% yield.

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