Synthesis of (1R,2S)-2-(4'-allyl-2',6'-dimethoxyphenoxyl)-1-(4''-hydroxy- 3'', 5''-dimethoxyphenyl)propan-1-ol

Article abstract of DOI:10.3184/174751911X13149759277234

The asymmetric synthesis of the natural neolignan (1R,2S)-2-(4'-allyl-2', 6'-dimethoxyphenoxyl)-1-(4''-hydroxy-3'',5''- dimethoxyphenyl)propan-1-ol based on an asymmetric dihydroxylation as a key reaction using AD-mix-β to preparing the chiral threo-(1R,2R)-glycerol. The reaction, threo-alcohols were inverted by an S_N2 reaction into erythro-(1R,2S)-isomers.

Full text of DOI:10.3184/174751911X13149759277234

JOURNAL OF CHEMICAL RESEARCH 2011
RESEARCH PAPER 519
SEPTEMBER, 519–521
Synthesis of (1R,2S)-2-(4’-allyl-2’,6’-dimethoxyphenoxyl)-1-(4’’-hydroxy-3’’,
5’’-dimethoxyphenyl)propan-1-ol
Junwei Ding, Rongwei Qi, Haitang Zhou, Bin Jiao and Yamu Xia*
College of Chemical Engineering, Qingdao University of Science andTechnology, Qingdao 266042, P. R. China
The asymmetric synthesis of the natural neolignan (1R,2S)-2-(4’-allyl-2’,6’-dimethoxyphenoxyl)-1-(4’’-hydroxy-3’’,5’’-
dimethoxyphenyl)propan-1-ol based on an asymmetric dihydroxylation as a key reaction using AD-mix-β to
preparing the chiral threo-(1R,2R)-glycerol. The reaction, threo-alcohols were inverted by an SN2 reaction into
erythro-(1R,2S)-isomers.
Keywords: synthesis, enantioselectivity, neolignan
The aril of Myristica fragrans Houtt. (Myristicaceae) has been
widely used as a spice and a valuable remedy in Ayurvedic
medicine for the treatment of low levels of fever, in consump-
tive complaints, asthma, and when mixed with aromatics,
in wasting and long-term bowel complaints.1–4 In 1987,
a new erythro-bisphenylpropanoid 2-(4′-allyl-2′,6′-dimethoxy-
phenoxyl)-1-(4″-hydroxy-3″,5″-dimethoxyphenyl)propan-1-
ol (1) was obtained from the aril of Myristica fragrans, and
shown to be a 8-O-4′-neolignan.5 8-O-4′-neolignans are a very
interesting class of natural products because of their pharma-
cological properties, and they have been shown to have
antioxidant, antimalarial and antileishmanial activities.6–8 The
synthesis of 8-O-4′-neolignans has been accomplished by
several methods, the majority of which have given racemic
mixtures of threo- and erythro-isomers.9–12 Zacchino reported
the stereoselective synthesis of threo-8-O-4′-neolignan, by
selecting the appropriate starting materials, and using the
mould Rhizopus nigricans to obtain the natural product Virolin
and to establish its configuration.13 Recently, the development
of a truly general and modular asymmetric route to threo- and
erythro-8-O-4′-neolignans compound class was outlined in a
nine-step sequence.14
(E)-6 in good yield. AlH3 can selectively reduce esters without
reducing alkenes. Asymmetric dihydroxylation of 6 with AD-
mix-β formed two chiral centres and gave threo-(1R,2R)-7.16
Treatment of 7 with TsCl in pyridine provided threo-(1R,2R)-
8. Because of steric hindrance, this reaction only occurred at
the primary hydroxyl of 7 with Tscl.17 Epoxide formation by
treatment with base yielded threo-(1R,2R)-9. The hydroxy
group of 9 was protected by DHP, and then ring opening by
LiAlH4 in THF gave threo-(1R, 2R)-10. The benzyl group
of compound 10 was removed, and then the hydroxyl group
was protected with MOMCl to give the key intermediate
threo-(1R, 2R)-11.
As shown in Scheme 3, 4-allyl-2,6-dimethoxyphenol (15)
was obtained, following a procedure which has been described
previously.17
As shown in Scheme 4, a Mitsunobu reaction between
threo-(1R,2R)-11 and compound 15 gave the erythro-
configuration, and the absolute configuration at the C-8 chiral
centre was inverted completely from R- to S-configuration.18
Then, the THP and MOM group were cleaved by HCl
in MeOH and the natural product (−)-(1R,2S)-2-(4′-Allyl-2′,
6′-dimethoxyphenoxyl)-1-(4-hydroxy-3,5-dimethoxyphenyl)
propan-1-ol (1) was obtained.
In conclusion, we have demonstrated the validity of our
methodology for the preparation of erythro-8-O-4′-neolignans
by the synthesis of (−)-(1R,2S)-2-(4′-allyl-2′,6′-dimethoxy-
phenoxyl)-1-(4″-hydroxy-3″,5″-dimethoxyphenyl)propan-1-
ol (1).
An effective approach is described here for the synthesis
of erythro-8-O-4′-neolignans based on a key reaction using
AD-mix-β to prepare chiral threo-(1R,2R)-glycerols and then
by an SN2 reaction, to invert the threo-alcohols to the erythro-
isomers. (1R,2S)-2-(4′-Allyl-2′,6′-dimethoxyphenoxyl)-1-(4″-
hydroxy-3″,5″-dimethoxyphenyl)propan-1-ol (1) was obtained
using this product.
Experimental
Results and discussion
Melting points were taken on Gallenkamp melting point apparatus
and are uncorrected. Optical rotations were determined on a Perkin-
Elmer 341 polarimeter. Chrial analysis was performed on Varian
Dynamax SD-300 using chiralcel column CDMPC (150 × 4.6 mm D)
with hexane/isopropyl alcohol as eluant. IR spectra were recorded on
As shown in Scheme 2, synthesis of the first part began from
compound 2. Demethylation of 3,4,5-trimethoxybenzalde-
hyde(2) by treatment with piperidine and H2O yielded com-
pound 3. This method was effective to cleave the 4-O-methyl
group of 3,4,5-trimethoxybenzaldehyde(2), whilst the 3-O-
methyl ether and 5-O-methyl ethers were stable under these
conditions.15 Protection of 3 with benzyl chloride afforded
compound 4. A Wittig reaction was carried out between
compound 4 and (Ph)3PCHCOOEt, to give the unsaturated
ester (E)-5. Reduction of (E)-5 with AlH3 which was prepared
from LAH/AlCl3 gave the corresponding unsaturated alcohol
1
a Nicolet NEXUS 670 FT−IR. The H NMR and 13C NMR spectra
were recorded on a Mercury Plus−300 MHz and Bruker–500 MHz
spectrometers. Mass spectra were recorded on a ZAB−HS spectrom-
eter. HRMS were obtained on a Bruker Daltonics APEXII47e spec-
trometer. Flash column chromatography was performed on silica gel
(200–300 mesh) and TLC inspections on silica gel GF254 plates.
4-Hydroxy-3,5-dimethoxybenzaldehyde (3): A solution of 3,4,5-
trimethoxy benzaldehyde(2) (15.6 g, 80 mmol) in piperidine/H2O
(1:1, 100 mL) was heated under reflux for 48 h and the cooled mixture
was poured into 4 N HCl. The mixture was extracted with AcOEt. The
organic layer was dried over MgSO4, filtered, then concentrated
in vacuo. Flash column chromatography of residue gave compound
3 as a white crystal (10.5 g, 72%). M.p. 111−112 °C. 1H NMR
(200 MHz, CDCl3), δ: 3.97 (s, 6H, 2 × OCH3), 7.16 (s, 2H, ArH), 9.82
(s, 1H, CHO). EI-MS, m/z: 182 (M+, 12.3), 167 (2.8), 139 (14.7), 91
(5.7), 65 (100).
4-Benzyloxy-3,5-dimethoxybenzaldehyde (4): To a well-stirred
solution of K2CO3 (7.0 g, 50 mmol) and compound 3 (9.0 g, 50 mmol)
in ethanol was added dropwise benzyl chloride (5.0 g, 50 mmol).The
mixture was stirred and warmed to reflux for 4 h, then concentrated
in vacuo. The residue was dissolved in AcOEt (100 mL), filtered, and
Scheme 1
* Correspondent. E-mail: xiaym@qust.edu.cn

520 JOURNAL OF CHEMICAL RESEARCH 2011
Scheme 2
Scheme 3
Scheme 4
washed with 10% aqueous NaOH and NaCl saturated solution for
3 times respectively. The extract was dried over MgSO4, filtered, then
concentrated in vacuo to remove AcOEt. The solids were recrystal-
lised in C2H5OH to yield the compound 4 as a colourless crystal
(12.2 g, 90%). M.p. 89–91 °C. 1H NMR (200 MHz, DMSO-d6),
δ: 3.94 (s, 6H, 2 × OCH3), 5.17 (s, 2H, ArCH2O), 7.18 (s, 2H, ArH),
7.23–7.64 (m, 5H, Ar-H), 9.84 (s, 1H, CHO). EI-MS, m/z: 272 (M+,
5.2), 257 (12.7), 229 (2.8), 91 (100), 51 (28.2).
(E)-4-benzyloxy-3,5-dimethoxyphenylcinnamyl alcohol (6): Dry
AlCl3 (3.4 g, 25 mmol) was added at 0 °C, to a suspension of LiAlH4
(1.0 g, 25 mmol) in dry THF (40 mL), the and stirred for 20 min to
obtain the reagent AlH3. Then compound 5 (8.6 g, 25 mmol) was
added. The mixture was stirred for 10 h at room temperature, and then
quenched with H2O, filtered, and concentrated in vacuo. Flash column
chromatography of residue gave 6 as a colourless oil (6.5 g, 86%).
1H NMR (200 MHz, CDCl3): 3.81 (s, 6H, 2 × OCH3), 4.28 (d, 2H,
J = 5.5 Hz, CH2OH), 5.01 (s, 2H, ArCH2O), 6.25 (dt, 1H, J = 5.5,
15.5 Hz, ArCH=CH), 6.51 (d, 1H, J = 15.5 Hz, ArCH=CH), 6.60
(s, 2H, ArH), 7.27–7.52 (m, 5H, ArH). EI-MS, m/z: 300 (M+, 8.3), 209
(12.1), 177 (4.7), 121 (15.3), 91 (100).
threo-(1R,2R)-1-(4′-Benzyloxy-3′,5′-dimethoxyphenyl)-1,2,3-glycerol
(7): AD-mix-β (27.8 g), MeSO2NH2 (2.0 g) were added to a stirred
solution of t-BuOH (40 mL) and H2O (40 mL), the mixture was stirred
at room temperature until both phases were clear, and then cooled to
0 °C. Compound 6 (6.0 g, 20 mmol) was added at once, and the mix-
ture was stirred vigorously at 0 °C until TLC revealed the absence of
6. The reaction was quenched at 0 °C by addition of Na2SO3 (30 g),
Ethyl (E)-4-benzyloxy-3,5-dimethoxyphenylcinnamate (5): The
compound 4 (10.9 g, 40 mmol) and (Ph)3PCHCOOEt (13.9 g,
40 mmol) in dry benzene was refluxed for 10 h, and then concentrated
in vacuo. Flash column chromatography of the residue gave com-
pound 5 as a white crystal (10.3 g, 75%). M.p. 71–72 °C (lit.19 m.p.
1
69 °C.). H NMR (200 MHz, CDCl3), δ: 1.35 (t, 3H, J = 7.5 Hz,
COCH2CH3), 3.85 (s, 6H, 2 × OCH3), 4.26 (q, 2H, J = 7.5 Hz,
COCH2CH3), 5.05 (s, 2H, ArCH2O), 6.35 (d, 1H, J = 16.0 Hz,
ArCH=CH), 6.74 (s, 2H, ArH), 7.30–7.52 (m, 5H, ArH), 7.60 (d, 1H,
J = 16.0 Hz, ArCH=CH). EI-MS, m/z: 342 (M+, 11.4), 297 (19.7),
251 (4.5), 91 (100).

JOURNAL OF CHEMICAL RESEARCH 2011 521
then warmed to room temperature and stirred for 0.5 h. The reaction
mixture was extracted withAcOEt (3 × 50 mL) and dried over MgSO4,
then the AcOEt was distilled off. Flash chromatography of the residue
over silica gel gave compound 7 (6.0 g, 90%) as a white crystal in
93% e.e.. M.p. 77–78 °C. [α]D20 = −18 (c 1.6, CHCl3) (lit.20 m.p. 78 °C.
[α]D20 = −18.). IR (KBr/cm−1): 3440, 2943, 2835, 1645, 1515, 1462,
1150. 1H NMR (300 MHz, CDCl3): 3.45–3.52 (m, 2H, CH2OH),
3.74–3.76 (m, 1H, CHOHCH2OH), 3.77 (s, 6H, 2 × OCH3), 4.55 (d,
J = 6.5 Hz, 1H, ArCHOH), 4.96 (s, 2H, ArCH2OAr), 6.55 (s, 2H,
ArH), 7.30–7.52 (m, 5H, ArH). EI-MS, m/z: 334 (M+, 1.8), 273 (3.9),
183 (15.7), 123 (4.8), 91 (100).
CDCl3), δ: 1.06 (d, 3H, J = 7.0 Hz, OHCHCH3), 1.44–1.75 (m, 6H,
CH2), 3.12–3.20 (m, 1H, CH2CH2O), 3.39–3.45 (m, 1H, CH2CH2O),
3.50 (s, 3H, OCH3), 3.83–4.05 (m, 7H, CHOHCH3, 2 × OCH3), 4.14
(d, 1H, J = 7.5 z, ArCHOTHP), 4.86−4.92 (m, 1H, OCHO), 5.23
(s, 2H, CH3OCH2OAr), 6.56 (s, 2H, ArH). EI-MS, m/z: 356 (M+, 0.8),
338 (1.6), 310 (10.7), 293 (5.2), 91 (100). HRMS Calcd for C18H32NO7
(M + NH4+): 374.2174. Found: 374.2170.
(1R,2S)-2-(4′-Allyl-2′,6′-dimethoxyphenoxyl)-1-(4″-hydroxyl-3″,
5″-dimethoxyphenyl) propan-1-ol (1): A mixture of (1R,2R)-11 (0.7 g,
2 mmol), compound 15 (0.4 g, 2 mmol), triphenylphosphine (0.6 g,
2 mmol) and diethylazodicarboxylate (0.3 mL, 2 mmol) was stirred in
dry THF (30 mL) at room temperature for 24 h under nitrogen. The
mixture was concentrated under reduced pressure. The residue was
added to a solution of HCl in MeOH (1 N, 30 mL), and the mixture
was stirred at room temperature for 8 h. The solution was neutralised
with NaHCO3 saturated solution. Subsequently the solvent was con-
centrated in vacuo and the residue was taken up inAcOEt. The organic
phase was washed with H2O, dried with MgSO4 and concentrated in
vacuo. Flash column chromatography of the residue over silica gel
gave product 1 (0.30 g, 38%) as gum. [α]D20 = −12.5 (c 0.1, CHCI3).
IR (KBr/cm−1): 3450, 2936, 2840, 1615, 1540, 1525, 1250, 1026. 1H
NMR (500 MHz, CDCl3), δ: 1.12 (d, 3H, J = 6.5 Hz, H-3), 3.37 (d,
2H, J = 6.5 Hz, H-7′), 3.86 (s, 6H, 2 × OCH3), 3.87 (s, 6H, 2 × OCH3),
4.27–4.35 (m, 1H, H-2), 4.78 (d, 1H, J = 3.0 Hz, H-1), 5.10–5.18
(m, 2H, H-9′), 5.92–6.08 (m, 1H, H-8′), 6.46 (s, 2H, H-3′, H-5′), 6.55
(s, 2H, H-2″, H-6″). 13C NMR (125 MHz, CDCl3), δ: 12.6 (C-3), 40.5
(C-7′), 56.1 (2 × OCH3), 56.3 (2 × OCH3), 73.2 (C-2), 82.4 (C-1),
103.1 (C-2″, C-6″), 105.7 (C-3′, C-5′), 116.1 (C-9′), 131.2 (C-4′),
133.7 (C-1″), 136.2 (C-1′), 137.0 (C-8′), 140.1 (C-4″), 147.1 (C-3″,
C-5″), 153.5 (C-2′, C-6′). EI-MS, m/z: 404 (M+, 4.6), 386 (10.5), 221
(17.8), 194 (100). HRMS Calcd for C22H29O7 (M + H+): 405.1908.
Found: 405.1911. The data were agreement with those reported in the
literature.5
threo-(1R,2R)-1-(4′-Benzyloxy-3′3′,5′-dimethoxyphenyl)-3-O-
tosyl-1,2-glycol (8): Compound 7 (5.0 g, 15 mmol) and pyridine
(15 mL) were added at room temperature to a solution of TsCl (2.9 g,
15 mmol) in CH2Cl2 (20 mL). The mixture was stirred vigorously
until TLC revealed the absence of 7. The mixture was quenched with
HCl solution, and then extracted with AcOEt. The organic layer was
washed with NaHCO3 and NaCl saturated solution respectively, then
was dried over MgSO4 and concentrated in vacuo. Flash chromato-
graphy of the residue over silica gel gave compound 8 (6.4 g, 87%) as
a white powder. M.p. 122–124 °C. [α]D20 = −10 (c 1.5, CHCl3) (lit.20
m.p. 123 °C. [α]D20 = −10.). IR (KBr/cm−1): 3438, 2927, 2835, 1640,
1
1521, 1420, 1318, 1235, 1106, 1025. H NMR (300 MHz, CDCl3):
2.44 (s, 3H, ArCH3), 3.79 (s, 6H, 2 × OCH3), 3.84–3.90 (m, 1H,
CHOHCH2OTs), 3.95–4.03 (m, 2H, CH2OTs), 4.60 (d, 1H, J = 6.0 Hz,
ArCHOH), 4.98 (s, 2H, ArCH2OAr), 6.55 (s, 2H, ArH), 7.30–7.76 (m,
9H, ArH). EI-MS, m/z: 488 (M+, 2.1), 470 (5.3), 424 (1.5), 334 (13.2),
172 (25.8), 91 (100).
threo-(1R,2R)-1-(4′-Benzyloxy-3′,5′-dimethoxyphenyl)-2,3-epoxy-
1-propanol (9): Compound 8 (4.9 g, 10 mmol) was added to a solution
of K2CO3 (2.1 g, 15 mmol) in methanol. The mixture was stirred at
room temperature for 5 h, and then the reaction mixture was concen-
trated in vacuo. The residue was dissolved in AcOEt and washed with
water and NaCl saturated solution for 3 times respectively.The extract
was dried over MgSO4 and concentrated in vacuo. Flash column chro-
matography of the residue over silica gel gave compound 9 (2.8 g,
88%). M.p. 98–100 °C. [α]D20 = −8 (c 1.0, CHCl3) (lit.20 M.p. 100 °C.
[α]D20 = −8.). IR (KBr/cm−1): 3448, 2940, 2836, 1735, 1604, 1592,
1515, 1459, 1250, 1137, 1024. 1H NMR (300 MHz, CDCl3), δ: 2.81–
2.88 (m, 2H, CHOCH2), 3.18–3.25 (m, 1H, CHCH2O), 3.81 (s, 6H,
2 × OCH3), 4.43 (d, 1H, J = 5.5 Hz, ArCHOHCH), 5.00 (s, 2H,
ArCH2OAr), 6.65 (s, 2H, ArH), 7.32–7.54 (m, 5H, ArH). EI-MS, m/z:
316 (M+, 7.2), 225 (1.5), 153 (12.6), 91 (100).
This work was financially supported by the National Natural
Science Foundation of Shandong (No. ZR2010HM023).
Received 5 July 2011; accepted 30 August 2011
Paper 1100774 doi: 10.3184/174751911X13149759277234
Published online: 30 September 2011
threo-(1R,2R)-1-(4′-Benzyloxy-3′,5′-dimethoxyphenyl)-1-O-2″-
tetrahydropyrane-2-propanol (10): DHP(0.7 g, 7 mmol), and a cata-
lytic amount of PPTS were added to a solution of compound 9 (2.2 g,
7 mmol) in dry CH2Cl2. The mixture was stirred at room temperature
until TLC revealed the absence of 9. Then the mixture was concen-
trated in vacuo. The residue was added to a solution of LiAlH4 (0.4 g,
10 mmol) in dry THF. The mixture was stirred at room temperature
for 24 h. The mixture was quenched with H2O, filtered and concen-
trated in vacuo. Flash column chromatography of the residue over
silica gel gave compound 10 (2.1 g, 75%) as colourless oil. IR (KBr/
cm−1): 3420, 2938, 2846, 1598, 1515, 1448, 1409, 1380, 1257, 1135,
1065, 1028. 1H NMR (300 MHz, CDCl3), δ: 1.05 (d, 3H, J = 6.8 Hz,
OHCHCH3), 1.45–1.75 (m, 6H, CH2), 3.16–3.24 (m, 1H, CH2CH2O),
3.41−3.49 (m, 1H, CH2CH2O), 3.83 (s, 6H, 2 × OCH3), 3.86–4.03 (m,
1H, CHOHCH3), 4.16 (d, 1H, J = 7.0 Hz, ArCHOTHP), 4.84− 4.93
(m, 1H, OCHO), 5.01 (s, 2H, ArCH2OAr), 6.58 (s, 2H, ArH), 7.30–
7.65 (m, 5H, ArH). EI-MS, m/z: 402 (M+, 1.5), 358 (2.4), 312 (8.3),
151 (4.2), 91 (100). HRMS Calcd for C23H31O6 (M + H+): 403.2116.
Found: 403.2118.
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