Intramolecular Carbonyl¨CCarbonyl Interaction as the Directing Motif of the Opposed Conformational Preferences Among [4?+?2] Cycloadducts of 3-Ethoxycarbonyl- and 3-Acetyl-Coumarins with 2,3-Dimethyl-1,3-Butadiene

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• 作者：Irma Y. Flores-Larios ; Francisco J. Mart¨ªnez-Mart¨ªnez ; Efr¨¦n V. Garc¨ªa-B¨¢ez ; Olivia Franco-Hern¨¢ndez and Itzia I. Padilla-Mart¨ªnez
• 关键词：Coumarins ; Diels– ; Alder adducts ; 6a ; 7 ; 7a ; 8a ; 9 ; 9a ; Hexahydro ; 7a ; 8a ; dimethyl ; 6 ; oxo ; 6H ; 5 ; 8 ; dioxacyclopropa[b]phenanthrenes
• 刊名：Journal of Chemical Crystallography
• 出版年：2010
• 出版时间：November 2010
• 年：2010
• 卷：40
• 期：11
• 页码：1024-1028
• 全文大小：315.0 KB

文摘

Abstract In this work, the molecular structures of the Diels–Alder adducts: ethyl (6aR/S,10aR/S)-6a,7,10,10a-tetrahydro-8,9-dimethyl-6-oxodibenzo[b,d]pyran-6a-carboxylate C₁₈H₂₀O₄ 1 and (6aR/S,10aR/S)-6a-acetyl-6a,7,10,10a-tetrahydro-8,9-dimethyl-6-oxodibenzo[b,d]pyran C₁₇H₁₈O₃ 2; and the epoxide of this last (6aR/S,7aR/S,8aS/R,9aR/S)-6a-acetyl-6a,7,7a,8a,9,9a-hexahydro-7a,8a-dimethyl-6-oxo-6H-5,8-dioxacyclopropa[b]phenanthrene C₁₇H₁₈O₄ 3, are comparatively analyzed. Compound 1 is triclinic, space group P-1 with a = 7.7529(6) ?, b = 9.8625(8) ?, c = 11.3103(9) ?, α = 109.387(9)¡ã, β = 95.484(1)¡ã, γ = 99.753(1)¡ã, Z = 2. Compound 2 is monoclinic, space group Cc, a = 7.7285(7) ?, b = 16.6813(15) ?, c = 11.3213(10) ?, β = 92.470(2)¡ã, Z = 4. Compound 3 is monoclinic, space group P2 ₁ /c a = 11.2036(10), b = 15.8326(14), c = 8.3182(7), β = 90.600(2)¡ã, Z = 4. The molecular structures of compounds 1–3 show conformational differences between lactone and 6a-acyl carbonyls. CO¡¤¡¤¡¤CO dipolar interactions stabilize the less favoured syn conformation in 2–3, conclusions are supported on theoretical calculations. The molecular structure of compound 3 demonstrates that epoxidation of 2 leads to the stereo-selective addition of the oxygen atom.