isopropyl ester 8, olefination of the intermediate aldehyde by isopropylidenetriphenylphosphorane, and removal of the THP
protection from 9 to give (R)-(+)-citronellol (10). The overall yield of target (2E,4)-1 as a mixture (4:1) of the 2E,4E- and
2E,4Z-stereoisomers (according to GC and PMR data) calculated for L-menthol (3) was 16%.
EXPERIMENTAL
PMR and IR spectra were obtained on equipment of the Khimiya CUC at UfIC, RAS. IR spectra were recorded from
thin layers on an IR-Prestige-21 FTIR spectrophotometer (Shimadzu). NMR spectra were taken in CDCl solutions with TMS
3
1
13
internal standard on a Bruker AM-300 spectrometer (operating frequency 300.13 MHz for H and 75.47 MHz for C).
Chromatography was performed on Chrom-5 [1.2-m column, SE-30 silicone (5%) stationary phase on Chromaton
N-AW-DMCS (0.16–0.20 mm, operating temperature 50–300°C] and Shimadzu GC-9A instruments (25-m quartz capillary
column, OV-101 stationary phase, operating temperature 80–280°C) with He carrier gas. Optical rotation was measured on
a Perkin-Elmer 241 MC polarimeter. TLC monitoring used Sorbfil SiO (Russia). Tiglic aldehyde (99%) was purchased
2
(Sigma-Aldrich). Isolation and chromatography used methyl-t-butylether (MTBE) and petroleum ether (40–70°C, PE).
2,6R-Dimethyl-8-(tetrahydro-2H-pyran-2-yloxy)octan-3-one (7). Hydroxyketone 6 (5.00 g, 29.1 mmol), which
was prepared from L-menthol (3) in four steps in 75% yield [4], in Et O (38 mL) was treated with DHP (4.47 g, 53.2 mmol,
2
8.9 mL), and TsOH (0.10 g, 0.6 mmol), stirred for 24 h at room temperature, diluted with Et O (100 mL), washed successively
2
with NaHCO solution (10%) and saturated NaCl solution, dried over Na SO , and evaporated to afford 7 (7.22 g, 97%),
3
2
4
20
1
[ꢂ] +18.0ꢁ (c 0.5, CHCl ). H NMR spectrum (ÑDCl , ꢃ, ppm, J/Hz): 0.89 (3Í, d, J = 6.2, ÑÍ -6), 1.06 (6Í, d, J = 6.8,
D
3
3
3
Í-1, ÑÍ -2), 1.00–1.40 (1Í, m, Í-6), 1.40–1.70 (8Í, m, Í-5, 7, 4ꢄ, 5ꢄ), 1.80–2.20 (2Í, m, Í-3ꢄ), 2.43–2.52 (2Í, m, Í-4), 2.53
3
13
(1Í, septet, J = 6.8, Í-2), 3.60–3.70 (4Í, m, Í-8, 6ꢄ), 4.50 (1Í, br.s, H-2ꢄ). C NMR spectrum (CDCl , ꢃ, ppm): 18.27 (ÑH ,
3
3
Ñ-1, ÑÍ -2), 19.30 (ÑH , ÑÍ -6), 19.53 and 19.64 (CH , Ñ-4ꢄ), 25.41 and 25.45 (CH , Ñ-5ꢄ), 29.60 (CH, Ñ-6), 29.78 (CH ,
3
3
3
2
2
2
Ñ-5), 30.70 and 30.73 (CH , Ñ-3ꢄ), 36.35 (CH , Ñ-7), 37.80 (CH , Ñ-4), 40.60 (CH, Ñ-2), 62.28 and 62.80 (CH , Ñ-6ꢄ), 65.70
2
2
2
2
(CH , Ñ-8), 98.69 and 98.90 (CH, Ñ-2ꢄ), 214.40 (Ñ, Ñ-3).
2
Isopropyl Ester of 4R-Methyl-6-(tetrahydro-2H-pyran-2-yloxy)hexanoic Acid (8). A suspension of a mixture
(9.40 g) containing m-CPBA (75%, 35.0 mmol) in anhydrous CHCl (94 mL) at room temperature was treated dropwise with
3
a solution of 7 (7.10 g, 27.7 mmol) in anhydrous CHCl (63 mL); stirred for 48 h; diluted with CH Cl (100 mL); washed
3
2
2
successively with saturated solutions of NaHCO , Na S O and NaCl; dried over MgSO ; and evaporated to afford 8 (6.41 g,
3
2
2
3
4
20
1
85%), [ꢂ] +2.6ꢁ (c 0.38, CHCl ). H NMR spectrum (ÑDCl , ꢃ, ppm, J/Hz): 0.90 (3Í, d, J = 6.2, ÑÍ -4), 1.21 (6Í, d,
D
3
3
3
J = 6.3, CH -7), 1.00–1.40 (1Í, m, Ñ-4), 1.50–1.70 (8Í, m, Í-3, 5, 4ꢄ, 5ꢄ), 1.80–2.20 (2Í, m, H-3ꢄ), 2.20–2.35 (2Í, m, Í-2),
3
13
3.60–3.70 (4Í, m, Í-6, 6ꢄ), 4.96 (1Í, septet, J = 6.3, H-7), 4.55 (1H, br.s, H-2ꢄ). C NMR spectrum (CDCl , ꢃ, ppm): 19.28
3
(ÑH , ÑÍ -4), 19.52 (CH , Ñ-4ꢄ), 21.13 (ÑH , 2ÑÍ -7), 25.41 (CH , Ñ-5ꢄ), 29.58 (CH, Ñ-4), 30.69 (CH , Ñ-3ꢄ), 32.01 (CH ,
3
3
2
3
3
2
2
2
Ñ-2), 32.34 (CH , Ñ-3), 36.26 (CH , Ñ-5), 62.80 (CH , Ñ-6ꢄ), 65.71 (CH , Ñ-6), 67.52 (CH, C-7), 98.70 (CH, Ñ-2ꢄ), 173.58
2
2
2
2
(Ñ, Ñ-1).
3R,7-Dimethyloct-6-en-1-ol (10). A solution of isopropylidenetriphenylphosphorane was prepared by adding a
solution of n-BuLi in hexane (21.9 mL, 25.6 mmol, 1.17 N) at –70°C (Ar) to a suspension of i-PrPPh I (1.10 g, 25.6 mmol) [5]
3
in anhydrous THF (59 mL), storing for 1 h at room temperature, adding successively at –70°C (Ar) a solution of 8 (6.30 g,
23.2 mmol) in anhydrous THF (20 mL) and a solution of DIBAH in toluene (11.8 mL, 47.2 mmol, 73%), storing (–70°C, 1 h;
20°C, 16 h), treating with cold H O (48 mL), and filtering through a Schott filter. The filtrate was dried over Na SO , filtered,
2
2
4
and evaporated. The solid was dissolved in MTBE (100 mL), filtered through a thin layer of Al O (5 cm), and evaporated.
2
3
The solid was chromatographed over silica gel (PE–MBTE, 10:1ꢅ5:1) to afford 9 (3.06 g, 55%), R 0.6 (PE–MTBE, 2:1).
f
13
The IR and PMR spectral data were identical to those reported earlier [6]. C NMR spectrum (CDCl , ꢃ, ppm): 17.5 and 25.5
3
(ÑH , 2ÑÍ -7), 19.6 (ÑH , ÑÍ -3), 19.6 (CH , Ñ-4ꢄ), 24.8 (CH , Ñ-5ꢄ), 25.4 (CH , Ñ-5), 29.6 (CH, Ñ-3), 30.7 (CH , Ñ-3ꢄ),
3
3
3
3
2
2
2
2
37.2 (CH , Ñ-2), 39.2 (CH , Ñ-4), 62.1 (CH , Ñ-6ꢄ), 65.8 (CH , Ñ-1), 98.8 (CH, Ñ-2ꢄ), 124.8 (CH, Ñ-6), 130.3 (Ñ, Ñ-7).
2
2
2
2
A solution of THP ester 9 (2.95 g, 12.3 mmol) and PPTS (0.31 g, 1.23 mmol) [7] in MeOH (98 mL) was stirred at 55°C for 3 h.
The solvent was vacuum evaporated. The solid was chromatographed over silica gel to afford 10 (1.92 g, 97%), R 0.5
f
22
22
13
(PE–MTBE, 2:1), [ꢂ] +5.51° (neat), lit. [ꢂ] +5.52° (neat) [8]. IR, PMR, and C NMR spectral data were identical to
D
D
those reported earlier [9].
462