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7 The authors in Ref. 6a state that their AL-1 is identical to that isolated by
Bohlmann et al. from Artemisia douglasiana although in Bohlmann’s
paper the enol ether stereochemistry is represented as Z- rather than E-.
F. Bohlmann, N. Ates, J. Jakupovic, R. M. King and H. Robinson, Phyto-
chemistry, 1982, 21, 2691.
8 E. L. Eliel, K. D. Hargrave, K. M. Pietrusiewicz and M. Manoharan, J.
Am. Chem. Soc., 1982, 104, 3635.
9 For example: L. Ma, F. Ge, C.-P. Tang, C.-Q. Ke, X.-Q. Li,
A. Althammer and Y. Ye, Tetrahedron, 2011, 67, 3533.
10 B. Wallnofer, O. Hofer and H. Greger, Phytochemistry, 1989, 28, 2687.
11 (a) The situation arises commonly in the total synthesis of natural pro-
ducts containing the 1,7-dioxaspiro[5.5]undecane core as articulated, for
example, in: K. Mori, H. Watanabe, K. Yanagi and M. Minobe, Tetrahe-
dron, 1985, 41, 3663; (b) For more general discussion see: F. Perron and
K. F. Albizati, Chem. Rev., 1989, 89, 1617.
12 M. G. Nonato, M. J. Garson, R. J. W. Truscott and J. A. Carver, Phyto-
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1973.
and dried over MgSO4 then concentrated in vacuo. Purification
by column chromatography (methanol–dichloromethane, 0 →
1%) afforded both diastereomers of the title compound (24ax/
24eq, dr = 15 : 85) as a pale yellow solid (130 mg, 79%). Rf
0.47 (methanol–dichloromethane, 0.5%); m.p. 164–166 °C;
νmax/cm−1 (thin film) 3030s, 2922s, 1770s, 1580m, 1341s,
1161s, 1101s; NMR data for 24ax: δH (400 MHz, CDCl3) 1.40
(1 H, ddd, J 13.5, 4.5, 2.5 Hz, H-10), 1.92 (1 H, tdd, J 13.5, 4.5,
3.0 Hz) and 1.97–2.03 (1 H, m, 2 × H-9), 2.42 (3 H, s, CH3),
2.50 (1 H, td, J 13.5, 4.5 Hz, H-10), 3.14 (1 H, dd, J 13.0, 1.5
Hz, H-7), 3.73–3.82 (1 H, m, H-8), 4.39 (1 H, ddd, J 13.0, 3.0,
2.0 Hz, H-7), 4.55 and 4.78 (2 × 1 H, 2 × d, J 12.0 Hz, CH2Ph),
5.99 (1 H, d, J 5.5 Hz, H-3), 7.29 (2 H, d, J 8.5 Hz, Ar),
7.30–7.44 (5 H, m, Ph), 7.52 (2 H, d, J 8.5 Hz, Ar), 7.80 (1 H,
d, J 5.5 Hz, H-4); δC (100 MHz, CDCl3) 21.6 (CH3), 25.2
(CH2), 32.4 (CH2), 46.6 (CH2), 68.7 (CH), 69.9 (CH2), 95.4 (C),
118.6 (CH), 127.2 (CH), 127.7 (CH), 127.8 (CH), 128.5 (CH),
129.9 (CH), 135.7 (C), 137.9 (C), 144.4 (C), 157.5 (CH), 169.9
(C); NMR data for 24eq: δH (400 MHz, CDCl3) 1.63 (1 H, ddd,
J 13.5, 4.0, 3.0 Hz, H-10), 1.79 (1 H, tdd, J 13.5, 11.0, 4.0 Hz,
H-9), 2.04 (1 H, td, J 13.5, 4.5 Hz, H-10), 2.11–2.17 (1 H, m,
H-9), 2.42 (3 H, s, CH3), 2.94 (1 H, t, J 11.0 Hz, H-7), 3.72
(1 H, tt, J 11.0, 4.5 Hz, H-8), 4.29 (1 H, ddd, J 11.0, 4.5, 1.5
Hz, H-7), 4.65 (2 H, s, CH2Ph), 5.99 (1 H, d, J 5.5 Hz, H-3),
7.29 (2 H, d, J 8.5 Hz, Ar), 7.31–7.41 (5 H, m, Ph), 7.46 (2 H,
d, J 8.5 Hz, Ar), 7.74 (1 H, d, J 5.5 Hz, H-4); δC (100 MHz,
CDCl3) 21.6 (CH3), 26.9 (CH2), 36.1 (CH2), 48.7 (CH2), 71.0
(CH2), 72.8 (CH), 94.4 (C), 118.8 (CH), 127.3 (CH), 127.6
(CH), 127.9 (CH), 128.5 (CH), 129.9 (CH), 135.0 (C), 138.0
(C), 144.7 (C), 156.9 (CH), 169.5 (C); HRMS (ESI+) found
436.1175; C22H23NNaO5S (MNa+) requires 436.1189.
15 A. S. Pilcher and P. DeShong, J. Org. Chem., 1993, 58, 5130.
16 Crystal data for compound 6ax: (colourless plate, 0.16 × 0.20 ×
0.24 mm): C8H10O4 Mr = 170.16; orthorhombic, space group Pbca; a =
7.0008(2) Å, b = 9.0561(2) Å, c = 24.0388(5) Å, β = 90°, V = 1524.06
(6) Å3; Z = 8; μ = 0.120 mm−1; Dcalc = 1.483 g cm−3; Reflections col-
lected = 3461; independent reflections = 1723 (Rint = 0.024); R values
[I > 2σ(I), 1276 reflections]: R1 = 0.0363, wR2 = 0.0972; ρmin/max
=
−0.34/0.32 e Å−3; CCDC 842957. Crystal data for compound 6eq: (col-
ourless block, 0.10 × 0.10 × 0.10 mm): C8H10O4 Mr = 170.16; monocli-
nic, space group P21/n; a = 7.5000(3) Å, b = 6.0089(2) Å, c = 17.9334
(7) Å, β = 94.8761(15)°, V = 805.28(5) Å3; Z = 4; μ = 0.113 mm−1; Dcalc
= 1.403 g cm−3; Reflections collected = 3347; independent reflections =
1822 (Rint = 0.023); R values [I > 2σ(I), 1492 reflections]: R1 = 0.0484,
wR2 = 0.1581; ρmin/max = −0.27/0.34 e Å−3; CCDC 842958.
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Equilibration experiments
Single butenolide spiroacetals (6–9) or spiro-N,O-acetals
(23, 24) (5–20 mg) were dissolved in CD3CN (0.6 mL) in
a standard NMR tube. Hydriodic acid (aq., 57% by weight,
1 mol%) was then added and equilibration monitored by
NMR spectroscopy. Equilibrium was usually reached within
30 min–24 h.
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This journal is © The Royal Society of Chemistry 2012
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