Molecules 2014, 19
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(11.7 g, 0.056 mol) was added with stirring. The reaction mixture was left stirring at 0 °C while
monitored on TLC. When all substrate was converted, diethyl ether was added and the solution washed
successively with 10% HCl and brine. The organic solution was dried (MgSO4) and concentrated
in vacuo to provide a crude oil, which was purified by flash chromatography (SiO2; ethyl acetate:hexane
1:4, Rf: 0.11) to afford white crystals of tosylate 7 (13.5 g, 61% yield over both steps); Mp. 69–71 °C;
1H-NMR (400 MHz, CDCl3) δ 0.87 (s, 3H), 0.89 (s, 3H), 1.00–2.00 (m, 7H), 2.43 (s, 3H), 4.06 (m, 1H)
4.14 (dd, 1H, J = 9.4 Hz, 3.9 Hz), 4.31 (t, 1H, J = 9.4 Hz), (m, 3H), 7.33 (d, 2H, J = 8 Hz), 7.78 (d, 2H,
J = 8 Hz). 13C-NMR (100 MHz, CDCl3) δ 17.13, 21.68, 23.72, 31.06, 32.40, 32.86, 40.62, 48.66, 65.75,
68.82, 127.88, 129.88, 133.12, 144.79. IR: 3558, 2933 cm−1. The spectra data are essentially in
agreement with those published [6].
3.3. 3,3-Dimethyl-2-Methylenecyclohexanone (4)
A solution of tosylate 7 (10.0 g, 0.032 mol) in acetone was treated with excess of Jones reagent
(100 mL). The solution was stirred at room temperature for 30 min and the acetone was evaporated. The
residue was diluted with water and extracted with diethyl ether. The combined organic extracts were
dried (MgSO4) and concentrated in vacuo to give the keto-tosylate (9.9 g,) that were used in the next
step without further purification. A solution of this in dry benzene (200 mL) and DBU (4.6 mL,
0.031 mol) was stirred for 2 h at room temperature. The reaction mixture was washed with water and the
organic phase dried (MgSO4). Evaporation of the solvents gave the methylenecyclohexanone 4 (4.45 g,
1
quantitative yield) over the two steps H-NMR (400 MHz, CDCl3) δ 1.09 (s, 6H), 1.55–1.65 (m, 2H),
2.75–2.95 (m, 2H), 2.40 (t, 2H, J = 13.6 Hz), 5.10 (d, 1H, J = 1.3 Hz), 5.63 (d, 1H, J = 1.3 Hz). 13C-NMR
(100 MHz, CDCl3) δ 19.80, 20.90, 22.69, 28.46, 29.65, 37.84, 38.59, 40.74, 116.14, 155.74, 203.90. IR
(film): 3097, 2961, 1690 cm−1. The spectra data are essentially in agreement with those published [6].
3.4. 5,5,9-Trimethylspiro[5.5]undec-8-en-1-one (2)
A solution of the enone 4 (3.80 g, 0.028 mol) and isoprene (8.5 mL, 0.085 mol) in dichloromethane
(20 mL) was cooled to −10 °C with stirring. A 25% solution of dimethylaluminum chloride in hexane
(0.034 mol, 19 mL) was added over five min. The solution was warmed to room temperature and stirred
for 4 h. The reaction mixture was poured into 100 mL of ice water and the resulting mixture was extracted
with diethyl ether. The organic extracts were combined, washed with brine and dried (MgSO4).
Evaporation of the solvents gave a residue that was purified by flash chromatography (SiO2; 1:4
1
EtOAc:hexane, Rf: 0.63) to provide the spiro ketone 2 (5.19 g; 90%) as a colorless oil. H-NMR
(400 MHz, CDCl3) δ 0.82 (s, 3 H), 0.98 (s, 3 H), 1.35 (dm, 1H, J = 14.0 Hz), 1.61 (s (br), 3 H), 1.7 (m,
2 H), 1.83 (m, 1 H), 1.85–1.90 (m, 3 H), 2.04 (td, 1 H, J = 13.3 Hz, 4.6 Hz), 2.20–2.26 (m, 2 H), 2.34
(dm, 1 H, J = 2.0 Hz, 3.5Hz), 2.65 (dt, 1H, J = 12.8Hz, 6.0Hz), 5.36 (d (br), 1H, J = 3.5 Hz). 13C-NMR
(100 MHz, CDCl3) 23.03, 23.19, 23.21, 24.79, 26.31, 27.02, 27.72, 35.52, 37.02, 40.77, 54.85, 120.44,
131.69, 214.88. IR (film): 2960, 1731 cm−1. The spectral data are in agreement with those published.