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DOI: 10.1055/s-2007-986635
Synthesis of [m,7,n]-Tricycles via Platinum-Catalyzed Cyclization of Conjugated Enynals with a Pendant Alkene
Publication History
Publication Date:
28 August 2007 (online)
Abstract
Conjugated enynals anchored to cycloalkenes, in the presence of platinum catalysts, were cyclized to the corresponding [m,7,n]-tricarbocycles, which are valuable skeletons in biologically active natural products like taxoids.
Key words
platinum - enynal - catalyst - cyclization - tetracycle
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References and Notes
The structure of product 5a was fully characterized by 1D and 2D NMR studies. 1H NMR, 13C NMR, DEPT, COSY, and HMQC spectra of 5a revealed the proposed structure. The proton connections of 5a were further confirmed by 1D TOCSY data. HMBC data showed the overall skeleton by long-range coupling and NOE studies confirmed its relative stereochemistry based on the proximity of Hα at C-12 with both H-11 and H-13 as shown in Table [3] .
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General Experimental Procedure for Cyclization: In a new 5 mL test tube, enynals 4a-i (0.3 mmol), PtCl2(PPh3)2 (5 mol%), and anhyd 1,4-dioxane (0.5 mL) were charged at 0 °C and the reaction mixture was kept under an argon atmosphere. The resulting mixture was stirred for 1-24 h in a preheated oil-bath (100 °C) with periodic monitoring of the reaction (TLC). Upon completion, the solvent was removed under vacuum and the crude product was subjected to flash column chromatography to afford the pure products 5a-e and 5g-i. In the case of substrate 4f, the reaction mixture was cooled to 0 °C and treated with a 1.0 M TBAF solution in THF (1.0 mmol). Extractive work-up and flash chromatography gave the desilylated 7f in 66% yield.
5a: 1H NMR (500 MHz, CDCl3): δ = 5.72 (s, 1 H), 5.49 (td, J = 1.6, 4.0 Hz, 1 H), 4.70 (d, J = 7.6 Hz, 1 H), 4.09-4.25 (m, 4 H), 2.67 (ddd, J = 4.4, 7.2, 8.8 Hz, 1 H), 2.66 (d, J = 14.4 Hz, 1 H), 2.51 (d, J = 14.4 Hz, 1 H), 2.31 (dd, J = 7.6, 13.6 Hz, 1 H), 2.28 (dd, J = 4.4, 13.6 Hz, 1 H), 2.24 (m, 2 H), 2.13 (ddd, J = 3.4, 7.2, 12.4 Hz, 1 H), 2.07 (m, 2 H), 1.89 (ddd, J = 0.8, 8.8, 12.4 Hz, 1 H), 1.70 (m, 1 H), 1.56 (m, 1 H), 1.25 (t, J = 7.2 Hz, 3 H), 1.24 (t, J = 7.2 Hz, 3 H). 13C NMR (125 MHz, CDCl3): δ = 172.27, 171.15, 137.79, 133.06, 127.12, 121.53, 90.82, 81.18, 62.77, 61.57, 61.35, 52.59, 42.14, 41.09, 40.82, 29.16, 25.31, 22.76, 14.03, 14.00. IR (NaCl): 1739, 1673, 1598 cm-1. HRMS: m/z calcd for C20H26NaO5: 369.1678; found: 369.1683.
6a: 1H NMR (400 MHz, CDCl3): δ = 4.52 (d, J = 6.4 Hz, 1 H), 4.13-4.27 (m, 4 H), 3.15 (d, J = 14.4 Hz, 1 H), 2.59 (m, 1 H), 2.56 (d, J = 14.4 Hz, 1 H), 2.43 (dd, J = 4.8, 13.6 Hz, 1 H), 2.38 (dd, J = 9.6, 13.6 Hz, 1 H), 2.17-2.31 (m, 2 H), 2.14 (ddd, J = 5.2, 6.8, 12.4 Hz, 1 H), 2.02-2.11 (m, 2 H), 1.99 (dd, J = 9.2, 12.4 Hz, 1 H), 1.67-1.81 (m, 2 H), 1.40-1.55 (m, 2 H), 1.27 (t, J = 7.2 Hz, 3 H), 1.24 (t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 195.06, 171.37, 171.25, 159.49, 129.00, 96.80, 80.08, 62.42, 61.94, 61.73, 44.92, 39.49, 37.36, 36.93, 26.97, 21.81, 21.72, 21.03, 14.28, 14.22. IR (NaCl): 1739, 1678, 1636 cm-1. HRMS: m/z calcd for C20H26NaO6: 385.1627; found: 385.1625.
5b: 1H NMR (400 MHz, CDCl3): δ = 5.73 (d, J = 1.2 Hz, 1 H), 5.63 (d, J = 2.0 Hz, 1 H), 4.99 (d, J = 8.4 Hz, 1 H), 4.10-4.26 (m, 4 H), 2.70 (d, J = 14.0 Hz, 1 H), 2.68 (ddd, J = 4.4, 7.2, 8.8 Hz, 1 H), 2.49 (d, J = 14.0 Hz, 1 H), 2.46 (m, 2 H), 2.44 (m, 2 H), 2.33 (dd, J = 7.2, 13.4 Hz, 1 H), 2.26 (dd, J = 9.2, 13.4 Hz, 1 H), 2.16 (ddd, J = 3.6, 7.2, 12.0 Hz, 1 H), 1.95 (ddd, J = 0.8, 8.8, 12.0 Hz, 1 H), 1.25 (t, J = 7.2 Hz, 3 H), 1.24 (t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 176.38, 171.20, 145.59, 144.45, 126.36, 120.74, 90.23, 80.15, 62.39, 61.56, 61.33, 52.37, 42.03, 41.08, 40.98, 31.36, 26.39, 14.02, 14.00. IR (NaCl): 1741, 1670, 1593 cm-1. HRMS: m/z calcd for C19H24NaO5: 355.1521; found: 355.1517.
5c: 1H NMR (400 MHz, CDCl3): δ = 5.62 (d, J = 2.0 Hz, 1 H), 5.54 (d, J = 1.2 Hz, 1 H), 4.84 (d, J = 7.2 Hz, 1 H), 4.10-4.28 (m, 4 H), 2.82 (dd, J = 10.8, 13.6 Hz, 2 H), 2.45-2.55 (m, 6 H), 1.97 (d, J = 14.0 Hz, 1 H), 1.55 (dd, J = 1.4, 12.2 Hz, 1 H), 1.24 (t, J = 7.2 Hz, 3 H), 1.23 (t, J = 7.2 Hz, 3 H), 1.09 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 172.54, 171.56, 146.59, 144.99, 126.22, 117.86, 91.62, 74.80, 61.57, 61.35, 59.97, 57.70, 49.49, 49.16, 40.76, 31.31, 26.42, 25.94, 13.98 (2 × C). IR (NaCl): 1740, 1675, 1595 cm-1. HRMS: m/z calcd for C20H26NaO5: 369.1678; found: 369.1674.
5d: 1H NMR (400 MHz, CDCl3): δ = 5.80 (s, 1 H), 5.48 (dd, J = 5.2, 6.0 Hz, 1 H), 4.66 (d, J = 7.2 Hz, 1 H), 4.10-4.26 (m, 4 H), 2.65 (d, J = 14.4 Hz, 1 H), 2.64 (ddd, J = 3.0, 8.4, 16.4 Hz, 1 H), 2.49 (d, J = 14.4 Hz, 1 H), 2.35 (m, 2 H), 2.17-2.31 (m, 4 H), 2.10 (ddd, J = 3.2, 7.6, 12.4 Hz, 1 H), 1.85 (ddd, J = 0.8, 8.4, 12.4 Hz, 1 H), 1.61-1.75 (m, 4 H), 1.24 (t, J = 7.2 Hz, 3 H), 1.23 (t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 172.30, 171.16, 139.96, 137.25, 130.01, 125.71, 90.27, 83.11, 62.46, 61.57, 61.35, 52.46, 41.65, 40.68, 40.52, 34.16, 27.62, 26.46, 25.89, 14.02, 14.00. IR (NaCl): 1731, 1448 cm-1. HRMS: m/z calcd for C21H28NaO5: 383.1834; found: 383.1833.
5e: 1H NMR (400 MHz, CDCl3): δ = 5.58 (s, 1 H), 5.42 (dd, J = 0.8, 2.0 Hz, 1 H), 4.85 (dd, J = 4.4, 5.6 Hz, 1 H), 4.30 (dq, J = 7.2, 12.0 Hz, 1 H), 4.19 (dq, J = 7.2, 14.4 Hz, 1 H), 4.15 (dq, J = 7.2, 14.4 Hz, 1 H), 4.08 (dq, J = 7.2, 12.0 Hz, 1 H), 2.78 (dd, J = 2.0, 15.2 Hz, 1 H), 2.37-2.53 (m, 4 H), 2.31 (dq, J = 1.6, 13.6 Hz, 1 H), 2.21 (d, J = 15.2 Hz, 1 H), 2.07 (m, 1 H), 1.80 (m, 2 H), 1.65 (m, 2 H), 1.47 (m, 1 H), 1.23 (t, J = 7.2 Hz, 3 H), 1.22 (t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 172.81, 170.86, 145.55, 144.20, 124.17, 122.90, 78.65, 72.91, 61.48, 60.96, 51.88, 43.90, 40.08, 36.03, 31.23, 29.46, 28.08, 26.53, 14.00, 13.95. IR (NaCl): 1737, 1670, 1599 cm-1. HRMS: m/z calcd for C20H26NaO5: 369.1678; found: 369.1680.
7f: 1H NMR (400 MHz, CDCl3): δ = 5.52 (s, 1 H), 5.43 (d, J = 4.4 Hz, 1 H), 4.16 (d, J = 5.6 Hz, 1 H), 3.26 (d, J = 4.8 Hz, 1 H), 2.75 (dq, J = 2.4, 12.0 Hz, 1 H), 2.05-2.34 (m, 7 H), 1.86 (m, 1 H), 1.68-1.77 (m, 2 H), 1.55-1.64 (m, 1 H), 1.22 (s, 3 H), 0.83 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 213.13, 134.61, 130.00, 122.96, 121.56, 80.57, 53.80, 44.42, 36.95, 33.12, 32.97, 31.35, 29.48, 26.09, 25.37, 23.01. IR (NaCl): 3465, 1753, 1663 cm-1. HRMS: m/z calcd for C16H22NaO2: 269.1517; found: 269.1520.
5g: 1H NMR (400 MHz, CDCl3): δ = 7.70 (d, J = 8.0 Hz, 2 H), 7.31 (d, J = 8.0 Hz, 2 H), 5.57 (s, 1 H), 5.51 (dd, J = 0.8, 4.4 Hz, 1 H), 4.65 (d, J = 8.8 Hz, 1 H), 3.69 (dd, J = 7.6, 8.0 Hz, 1 H), 3.51 (s, 2 H), 3.50 (m, 1 H), 2.70-2.83 (m, 2 H), 2.43 (s, 3 H), 2.23 (m, 2 H), 2.08 (m, 2 H), 1.98 (ddd, J = 1.6, 7.2, 12.8 Hz, 1 H), 1.77 (ddd, J = 1.2, 8.0, 12.8 Hz, 1 H), 1.68 (m, 1 H). 13C NMR (100 MHz, CDCl3): δ = 147.37, 143.21, 142.00, 129.64, 127.62, 123.43, 122.19, 118.67, 89.17, 80.82, 55.14, 54.34, 52.12, 36.89, 28.80, 24.94, 21.55. IR (NaCl): 1598, 1472 cm-1. HRMS: m/z calcd for C20H23NNaSO3S: 380.1296; found: 380.1294.
5h: 1H NMR (400 MHz, CDCl3): δ = 7.72 (d, J = 8.4 Hz, 2 H), 7.32 (d, J = 8.4 Hz, 2 H), 5.65 (d, J = 1.2 Hz, 1 H), 5.59 (dd, J = 1.4, 3.2 Hz, 1 H), 4.97 (d, J = 6.8 Hz, 1 H), 3.68 (dd, J = 7.6, 8.0 Hz, 1 H), 3.50 (ABq, Δδ = 13.2 Hz, J = 11.2 Hz, 2 H), 2.79 (ddd, J = 2.4, 8.8, 16.4 Hz, 1 H), 2.75 (dd, J = 9.2, 16.4 Hz, 1 H), 2.40-2.47 (m, 4 H), 2.43 (s, 3 H), 1.99 (ddd, J = 2.0, 7.6, 12.8 Hz, 1 H), 1.82 (ddd, J = 1.6, 8.0, 12.8 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 147.10, 143.82, 143.47, 133.24, 129.64, 127.66, 127.15, 117.64, 94.45, 88.90, 55.32, 54.60, 52.31, 37.42, 31.36, 26.44, 21.57. IR (NaCl): 1597, 1457 cm-1. HRMS: m/z calcd for C19H21NNaSO3S: 366.1140; found: 366.1144.
5i: 1H NMR (400 MHz, CDCl3): δ = 7.71 (d, J = 8.4 Hz, 2 H), 7.30 (d, J = 8.4 Hz, 2 H), 5.63 (d, J = 2.0 Hz, 1 H), 5.45 (s, 1 H), 4.83 (d, J = 6.8 Hz, 1 H), 3.53 (ABq, Δδ = 16.0 Hz, J = 12.0 Hz, 2 H), 3.40 (d, J = 8.8 Hz, 1 H), 3.06 (d, J = 8.8 Hz, 1 H), 2.47 (m, 4 H), 2.42 (s, 3 H), 2.25 (dd, J = 7.6, 12.4 Hz, 1 H), 1.42 (dd, J = 1.2, 12.8 Hz, 1 H), 1.12 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 147.95, 144.43, 143.26, 133.66, 129.55, 127.48, 126.72, 115.02, 89.95, 75.18, 60.72, 57.91, 54.20, 43.90, 31.26, 26.49, 21.52, 21.01. IR (NaCl): 1599, 1455 cm-1. HRMS: m/z calcd for C20H23NNaSO3S: 380.1296; found: 380.1298.