Molecules 2014, 19
1245
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of 10 as light yellow oil. H-NMR (300 MHz, CDCl3): δ = 5.40–5.35 (m, 1H, =CH2), 4.91–4.62 (m,
3H, =CH2, =CH-, -OCH(-O-)CH2-), 4.62–4.60 (d, 2H, J = 6.9 Hz, -CH2O-), 3.99–3.95 (m, 2H,
-OCH2-), 3.87–3.82 (m, 2H, -OCH2-), 3.03 (s, 2H, -CH2CO-), 2.17 (t, 2H, J = 8.1 Hz, -CH2-), 1.82 (s,
3H, -CH3), 1.80-1.75 (m, 2H, -CH2-), 1.72 (s, 3H, -CH3). 13C-NMR (150 MHz, CDCl3): δ = 16.4, 22.3,
31.9, 33.5, 43.3, 61.3, 64.8, 103.9, 114.5, 118.4, 138.5, 141.4, 171.2. ESI-MS (m/z): 277.1 (M+Na)+.
HRMS (ESI): calcd for C14H23O4 (M+H)+, 255.1596, found 255.1603.
(3S)-3-(2-(1,3-Dioxolan-2-yl)ethyl)-3-methyl-2-(prop-1-en-2-yl)pent-4-enoic Acid (11). A solution of 2
equiv. of LDA in dry THF (3 mL, 2 M) was cooled to −78 °C. To this stirred solution was added
1.0 equiv. of the ester 10 (0.76 g, 3 mmol), dropwise over 10 min. Following the addition, the reaction
mixture was stirred at −78 °C for 10 min and the 2 equiv. of Me3SiCl (0.76 mL, 6 mmol) in THF (6 mL)
was added dropwisely to the reaction mixture for 10 min. The reaction mixture was stirred at −78 °C
for 1.5 h and allowed to warm to 25 °C for 2 h. After the reaction was quenched with 1 N NaOH (20 mL)
and the organic phase was washed with 1 N NaOH (15 mL), the aqueous phases were combined and
acidified by HCl (5%) to pH = 1. the mixture was extracted with Et2O (3 × 15 mL), dried with
anhydrous MgSO4, filtered and concentrated in vacuo to afford the crude acid, which was purified by
silica gel chromatography (5% MeOH/CH2Cl2) to give 0.55 g (72%) of 11 as an inseparable mixture of
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diastereomers (dr = 2:1), as a light yellow oil. H-NMR (300 MHz, CDCl3): δ (mixture of two
diastereomers) = 6.05 and 5.84 (dd, 1H, J = 10.8, 17.5 Hz, -CH=), 5.12–4.95 (m, 4H, =CH2, =CH2),
4.82 (t, 1H, J = 2.1 Hz, -OCH(-O-)CH2-), 3.97–3.89 (m, 2H, -OCH2-), 3.85–3.81 (m, 2H, -OCH2-),
3.06 (s, 1H, 4-H), 1.85 (s, 3H, -CH3), 1.69–1.55 (m, 4H, -CH2CH2-), 1.16 and 1.11 (s, 1H, -CH3).
13C-NMR (150 MHz, CDCl3): δ = 19.4, 23.8/24.5, 28.8, 32.5/33.4, 42.0, 61.2/61.8, 63.6/64.8, 104.8,
114.0/114.3, 117.1/117.5, 139.7, 143.2/143.5, 177.4. HRMS (ESI): calcd for C14H23O4 (M+H)+, 255.1596,
found 255.1564.
(3S)-3-(2-(1,3-Dioxolan-2-yl)ethyl)-3-methyl-2-(prop-1-en-2-yl)pent-4-en-1-ol (12). To a stirred
solution of LiAlH4 (1.5 g, 39.3 mmol) in dry THF (15 mL) was added dropwise the inseparable
mixture of 11 (2.0 g, 7.9 mmol) in dry THF (20 mL) at 0 °C over 10 min. The reaction mixture was
stirred at room temperature for 5 h and allowed to warm to reflux for 1 h. The mixture was quenched
successively by H2O (1.5 mL), NaOH (15%, 1.5 mL) and 4.5 mL H2O on the ice-bath condition and
stirred at room temperature for 30 min. The white precipitation was filtered and washed with Et2O
(2 × 10 mL). All the organic phases were combined, dried (anhydrous MgSO4), filtered and
concentrated in vacuo to give the crude product, which was purified by silica gel chromatography
(EtOAc/petroleum ether, 5:95) to afford 1.58 g (83%) of 12 as an inseparable mixture of diastereomers
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(dr = 2:1), light yellow oil. Rf = 0.35 (EtOAc/petroleum ether, 1:3). H-NMR (300 MHz, CDCl3): δ
(mixture of two diastereomers) = 5.77 and 5.72 (dd, 1H, J = 10.8, 17.5 Hz, -CH=), 5.11–4.79 (m, 5H,
=CH2, =CH2, -OCH(-O-)CH2-), 3.95–3.93 (m, 2H, -OCH2-), 3.85–3.83 (m, 2H, -OCH2-), 3.77–3.59
(m, 2H, -CH2OH), 2.25–2.22 (m, 1H, 4-H), 1.79 and 1.79 (s, 3H, -CH3), 1.57–1.48 (m, 4H, -CH2CH2-),
1.03 and 0.98 (s, 1H, -CH3). 13C-NMR (150 MHz, CDCl3): δ = 17.7, 25.3, 28.5, 35.4, 41.1, 60.8/61.9,
62.4, 64.9/65.4, 102.2, 110.3, 113.1, 144.7, 149.7. HRMS (ESI): calcd for C14H25O3 (M+H)+,
241.1804, found 241.1794.