K. R. Prasad, P. Anbarasan / Tetrahedron: Asymmetry 18 (2007) 1419–1427
1423
127.6, 114.9, 108.8, 77.9, 77.4, 72.4, 30.0, 29.9, 27.2; HRMS
for C29H38O4+Na calcd 473.2668; found 473.2663.
J = 11.4 Hz, 4H), 3.63 (t, J = 4.2 Hz, 2H), 3.54 (q,
J = 5.4 Hz, 2H), 2.80 (d, J = 4.2 Hz, 2H), 2.12–2.00 (m,
4H), 1.79–1.40 (m, 8H); 13C NMR (75 MHz, CDCl3): d
138.4, 138.2, 128.5, 127.9, 127.8, 114.8, 80.5, 72.3, 71.9,
33.8, 29.4, 24.5; HRMS for C28H38O4+Na calcd
461.2668; found 461.2657.
4.4.2. (4S,5S)-4,5-Bis((R)-1-(benzyloxy)hex-5-enyl)-2,2-di-
methyl-1,3-dioxolane 6b. Colorless oil; Yield 97%;
[a]D = À8.1 (c 2.5, CHCl3); IR (neat): 2983, 2861, 1639,
1
1454, 1369, 1249, 1072, 912 cmÀ1; H NMR (300 MHz,
CDCl3): d 7.37–7.23 (m, 10H), 5.77 (ddt, J = 17.4, 10.2,
6.6 Hz, 2H), 5.03–4.91 (m, 4H), 4.60 and 4.52 (AB q,
J = 11.7 Hz, 4H), 4.10 (s, 2H), 3.41–3.35 (m, 2H), 2.08–
1.98 (m, 4H), 1.65–1.36 (m, 8H), 1.42 (s, 6H); 13C NMR
(75 MHz, CDCl3): d 138.6, 138.5, 128.3, 127.9, 127.6,
114.7, 108.8, 78.1, 78.0, 72.4, 33.7, 30.3, 27.2, 25.2; HRMS
for C31H42O4+Na calcd 501.2981; found 501.3000.
4.5.3. (7R,8R,9R,10R)-7,10-Bis(benzyloxy)hexadeca-1,15-
diene-8,9-diol 2c. White solid; Yield 93%; mp 49.5–
50.5 ꢁC; [a]D = À27.7 (c 2.7, CHCl3); IR (KBr): 3460,
2929, 2859, 1639, 1496, 1454, 1207, 1069, 910, 734,
1
697 cmÀ1; H NMR (300 MHz, CDCl3): d 7.42–7.22 (m,
10H), 5.79 (ddt, J = 16.9, 10.2, 6.6 Hz, 2H), 5.07–4.91
(m, 4H), 4.63 and 4.47 (AB q, J = 11.4 Hz, 4H), 3.63 (br
t, J = 4.2 Hz, 2H), 3.60–3.49 (m, 2H), 2.82 (d,
J = 4.2 Hz, 2H, exchangeable with D2O), 2.13–1.98 (m,
4H), 1.79–1.52 (m, 4H), 1.50–1.29 (m, 8H); 13C NMR
(75 MHz, CDCl3): d 138.7, 138.1, 128.4, 127.9, 127.8,
114.4, 80.5, 72.1, 71.8, 33.6, 29.6, 29.1, 24.6; HRMS for
C30H42O4+Na calcd 489.2981; found 489.2984.
4.4.3. (4S,5S)-4,5-Bis((R)-1-(benzyloxy)hept-6-enyl)-2,2-di-
methyl-1,3-dioxolane 6c. Colorless oil; Yield 91%;
[a]D = À6.4 (c 2.5, CHCl3); IR (neat): 2932, 2860, 1639,
1454, 1379, 1270, 1070, 911, 751, 698 cmÀ1 1H NMR
;
(300 MHz, CDCl3): d 7.42–7.20 (m, 10H), 5.78 (ddt,
J = 17.1, 10.2, 6.6 Hz, 2H), 5.06–4.90 (m, 4H), 4.60 and
4.51 (AB q, J = 11.7 Hz, 4H), 4.10 (s, 2H), 3.36 (br t,
J = 6.3 Hz, 2H), 2.08–1.98 (m, 4H), 1.66–1.54 (m, 4H),
1.48–1.27 (m, 8H), 1.43 (s, 6H); 13C NMR (75 MHz,
CDCl3): d 138.8, 138.5, 128.3, 127.8, 127.5, 114.4, 108.6,
77.9, 72.3, 33.6, 30.6, 28.9, 27.2, 25.5; HRMS for
C33H46O4+Na calcd 529.3294; found 529.3294.
4.6. General procedure for the preparation of (R)-2-(benz-
yloxy)alken-1-ol 7a–c
To a solution of 2a–c (0.34 mmol) in 3 mL of benzene at
room temperature was added Pb(OAc)4 (0.27 g, 0.6 mmol)
under an argon atmosphere. The reaction mixture was stir-
red for 1.5 h at the same temperature, quenched with
0.2 mL of water and then stirred for 10 min at room tem-
perature after which it was filtered through a short pad
of Celite. The Celite pad was washed with dichloromethane
(25 mL) and the combined organic layers dried over
Na2SO4. The solvent was evaporated under reduced pres-
sure to yield a-benzyloxy aldehyde 1a–c as colorless oil,
which was used as such without further purification.
4.5. General procedure for the preparation of bis(benzyloxy)-
alkene-diols 2a–c
To a solution of 6a–c in 5 mL of dry dichloromethane at
room temperature was added FeCl3Æ6H2O (0.85 g,
3.2 mmol) under an argon atmosphere. The reaction mix-
ture was stirred for 2.5 h at room temperature, and then fil-
tered through a short pad of Celite. The Celite pad was
then washed with dichloromethane (25 mL). The combined
organic layer was washed with satd NaHCO3 (3 · 15 mL),
brine (10 mL) and dried over Na2SO4. Evaporation of the
solvent under reduced pressure and purification of resul-
tant residue by column chromatography using petroleum
ether–ethyl acetate (3:1) resulted in 2a–c.
To a solution of a-benzyloxy aldehyde 1a–c (obtained
above) in 5 mL of MeOH at 0 ꢁC was added NaBH4
(52 mg, 1.36 mmol) under an argon atmosphere. The reac-
tion mixture was stirred for 1 h at the same temperature. It
was quenched by the cautious addition of water and ex-
tracted with diethyl ether (3 · 5 mL). The ether layer was
washed with brine (10 mL), dried over Na2SO4, filtered,
and evaporated. The residue thus obtained was subjected
to column chromatography using petroleum ether–ethyl
acetate (8:2) as an eluent to yield 7a–c.
4.5.1. (5R,6R,7R,8R)-5,8-Bis(benzyloxy)dodeca-1,11-diene-
6,7-diol 2a. Colorless oil; Yield 94%; [a]D = À24.4 (c 1.8,
CHCl3); IR (neat): 3440, 3295, 2923, 2850, 1641, 1454,
1
1398, 1099, 997, 732 cmÀ1; H NMR (300 MHz, CDCl3):
d 7.37–7.25 (m, 10H), 5.81 (ddt, J = 16.8, 10.2, 6.6 Hz,
2H), 5.07–4.94 (m, 4H), 4.64 and 4.49 (AB q,
J = 11.4 Hz, 4H), 3.66 (t, J = 3.9 Hz, 2H), 3.56 (q,
J = 5.4 Hz, 2H), 2.80 (d, J = 4.5 Hz, 2H), 2.22–2.08 (m,
4H), 1.87–1.60 (m, 4H); 13C NMR (75 MHz, CDCl3): d
138.2, 138.1, 128.5, 127.9, 127.8, 114.9, 80.1, 72.3, 71.7,
29.4, 29.2; HRMS for C26H34O4+Na calcd 433.2355;
found 433.2346.
4.6.1. (R)-2-(Benzyloxy)hex-5-en-1-ol 7a. Colorless oil;
Yield 89%; [a]D = –10.8 (c 3.5, CHCl3); IR (neat): 3413,
2923, 2863, 1639, 1454, 1058, 912, 738 cmÀ1 1H NMR
;
(300 MHz, CDCl3): d 7.37–7.23 (m, 5H), 5.79 (ddt,
J = 17.1, 10.2, 6.6 Hz, 1H), 5.07–4.91 (m, 2H), 4.60 and
4.54 (AB q, J = 11.4 Hz, 2H), 3.74–3.62 (m, 1H), 3.59–
3.46 (m, 2H), 2.18–2.07 (m, 3H), 1.79–1.54 (m, 2H); 13C
NMR (75 MHz, CDCl3): d 138.3, 138.1, 128.4, 127.7,
114.9, 79.1, 71.5, 64.0, 30.0, 29.5; HRMS for
C13H18O2+Na calcd 229.1204; found 229.1193.
4.5.2.
(6R,7R,8R,9R)-6,9-Bis(benzyloxy)tetradeca-1,13-
diene-7,8-diol 2b. Colorless oil; Yield 89%; [a]D = –25.8
(c 2.1, CHCl3); IR (neat): 3437, 2930, 2862, 1638, 1455,
4.6.2. (R)-2-(Benzyloxy)hept-6-en-1-ol 7b. Colorless oil;
Yield 93%; [a]D = –11.8 (c 1.9, CHCl3); lit.3e [a]D = À12.2
(c 1.8, CHCl3); IR (neat): 3415, 2933, 2861, 1639, 1454,
1088, 910, 732 cmÀ1 1H NMR (300 MHz, CDCl3): d
;
7.38–7.24 (m, 10H), 5.78 (ddt, J = 16.8, 10.2, 6.6 Hz,
2H), 5.06–4.93 (m, 4H), 4.64 and 4.48 (AB q,
1
1396, 1066, 910, 734 cmÀ1; H NMR (300 MHz, CDCl3):