Synthesis of enantiomerically pure (R)-and (S)-1-benzoyloxypropane-2,3-diol and revision of the stereochemical outcome of the Candida antarctica lipase-catalyzed benzoylation of glycerol

Article abstract of DOI:10.1016/j.tetasy.2011.04.003

Enantiomerically pure (R)- and (S)-1-benzoyloxypropane-2,3-diol have been prepared from (S)-(+)-2,2-dimethyl-1,3-dioxolane-4-methanol and used as reference compounds to correct the reported stereochemical outcome of the Candida antarctica lipase (CAL)-cat

Full text of DOI:10.1016/j.tetasy.2011.04.003

Tetrahedron: Asymmetry 22 (2011) 658–661
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Synthesis of enantiomerically pure (R)-and (S)-1-benzoyloxypropane-2,3-diol
and revision of the stereochemical outcome of the Candida antarctica
lipase-catalyzed benzoylation of glycerol
Silvana Casati a, Pierangela Ciuffreda a, Enzo Santaniello b,
⇑
a Università degli Studi di Milano, Dipartimento di Scienze Cliniche ‘L. Sacco’, via G.B. Grassi 74, 20157 Milano, Italy
b Università degli Studi di Milano, Dipartimento di Medicina, Chirurgia e Odontoiatria, via di Rudinì 8, 20142 Milano, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Enantiomerically pure (R)- and (S)-1-benzoyloxypropane-2,3-diol have been prepared from (S)-(+)-2,2-
dimethyl-1,3-dioxolane-4-methanol and used as reference compounds to correct the reported stereo-
chemical outcome of the Candida antarctica lipase (CAL)-catalyzed benzoylation of glycerol.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 7 February 2011
Accepted 6 April 2011
Available online 4 May 2011
1. Introduction
Although it could appear contradictory that opposite enantio-
mers exhibit the same positive specific rotation, this might tenta-
Mono-derivatives of glycerol 1a, such as 3-benzyloxypropane-
1,2-diol 1b or 1-benzoyloxypropane-2,3-diol 1c (Fig. 1), are valu-
able chiral synthons that have already been used in asymmetric
synthesis.1
tively be explained by the fact that measurements were recorded
in different solvents. In fact, the value of ½a D20
ꢀ
recorded in pyridine
for (S)-(+)-1c was +15.2 (c 2),2 whereas the sample of (R)-(+)-1c
showed an ½a 2D0
ꢀ
¼ þ18:8 (c 1.00, ethanol).5
However, (ꢁ)-1c has been prepared from
D
-1,2-isopropylidene-
-glycerol
-glycerol {[
sn-glycerol 38 and has been named 1-benzoyl-
D
OH
O
PhOCO
OH
{[a]
D = ꢁ17.5 (c 10, pyridine)}9 or 1-benzoyl-
L
a] =
D
O
OH
R
ꢁ15 (c 10, pyridine)}1a or (2R)-3-benzoyloxypropane-1,2-diol.1b
1
2
Finally, in a recent paper10 (R)-monobenzoate glycerol with a
high enantiomeric excess was used in isotopic 13C NMR spectros-
copy to measure the site-specific 13C/12C ratios at natural abun-
a. R = H
b. R = CH2Ph
c. R = COPh
dance. The authors specifically refer to
a sample of (R)-
Figure 1. Structure of compounds 1a–c and 2.
monobenzoate prepared using the CAL-catalyzed benzoylation of
prochiral glycerol 1a.5
A biocatalytic preparation of enantiomerically pure (S)-(+)-1c,
specifically the Baker’s yeast fermentation of 1-benzoyloxy-3-
hydroxypropan-2-one 2, was reported a few years ago.2 This result
has been later confirmed and extended to the bioreduction of other
dihydroxyacetone derivatives.3 Compound (S)-(+)-1c can been pre-
pared from 1-benzoyloxy-3-hydroxypropan-2-one 2 by also utiliz-
ing other microrganisms.4 Recently, a reported enzyme-assisted
asymmetrization of prochiral glycerol 1a has completed the avail-
ability of both enantiomeric 1-benzoyloxypropane-2,3-diols 1c.5–7
Specifically, it has been reported that the lipase from Candida ant-
arctica (CAL) catalyzes the benzoylation of glycerol 1a in organic
solvents and the optically active (R)-(+)-1-benzoyloxypropane-
2,3-diol 1c (max 60% ee) can be prepared.5 Re-crystallization in
the presence of enantiomerically pure 1c allows the preparation
of enantiomerically pure 1c in gram quantities (Scheme 1).5,6
It seemed necessary to establish unequivocally the configura-
tion and the specific rotation value of (R)-and (S)-1-benzoyloxy-
propane-2,3-diol 1c and for this purpose we have prepared
samples of (R)- and (S)-1c starting from (S)-(+)-2,2-dimethyl-1,3-
dioxolane-4-methanol 3, which can be prepared from D
-mannitol11
and is commercially available.
2. Results and discussion
The chemical synthesis of (S)-1-benzoyloxypropane-2,3-diol 1c
from (S)-(+)-2,2-dimethyl-1,3-dioxolane-4-methanol is de-
3
scribed in Scheme 2. Thus, acetonide 3 was converted into (S)-4
in a conventional manner12 and the acetonide protection of com-
pound (S)-4 satisfactorily removed by hydrolysis in the presence
of a resin with a sulfonic acid functionality (Amberlyst 15).13
(R)-3-Benzyloxypropane-1,2-diol 1b was then selectively
monobenzoylated to (S)-5 utilizing the recently described enzy-
⇑
Corresponding author. Tel.: +39 025 031 9691; fax: +39 025 031 9631.
E-mail address: enzo.santaniello@unimi.it (E. Santaniello).
0957-4166/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2011.04.003

S. Casati et al. / Tetrahedron: Asymmetry 22 (2011) 658–661
659
OH
O
OH
OH
Ph
O
OH
Ph
O
OH
Ph
O
OH
b
a
HO
OH
O
O
O
(S)-(+)-1c
1a
(R)-(+)-1c
2
b. microbial reductions (literature 3-5
)
a. Candida antarctica lipase, vinyl benzoate,
organic solvents (literature 6-8
)
Scheme 1. Biocatalytic approach to (R)- and (S)-1-benzyloxypropane-2,3-diol 1c, according to the literature.3–8
O
O
OH
(S)-3
a
e
OH
O
b
HO
O
Ph
Ph
O
O
O
Ph
O
O
(R)-1b
(S)-4
(R)-6
O
c
f
OH
OH
Ph
O
OH
Ph
O
O
Ph
OH
d
HO
O
Ph
O
O
(S)-1c
(S)-5
O
(R)-1c
Scheme 2. Reagents and conditions: (a) BnBr, NaH, THF, rt, 3 h, 76%; (b) Amberlyst 15, MeOH, rt, 3 h, 85%; (c) BzCl, TEA, CH2Cl2, rt, 1 h, 67%; (d) Pd/C, MeOH, rt, 6 h, 81%; (e)
BzCl, TEA, CH2Cl2, rt, 1 h, 72%; (f) Amberlyst 15, MeOH, rt, 3 h, 87%.
matic regioselective benzoylation procedure.14 Removal of the
3. Conclusion
benzyl protection by hydrogenolysis afforded quantitatively a
sample of pure (S)-(+)-1c (Scheme 2). The enantiomeric excess of
the sample obtained by our chemical synthesis was established
as >98% by analysis of the 1H NMR of the related Mosher ester.15
The specific rotations of (S)-1-benzoyloxypropane-2,3-diol 1c were
Starting from
D-1,2-isopropylidene-sn-glycerol [(S)-(+)-2,2-di-
methyl-1,3-dioxolane-4-methanol] 3, we have prepared enantio-
merically pure (R)-(ꢁ) and (S)-(+)-1c. Therefore, the (+)-
monobenzoate 1c that has been prepared by the CAL-catalyzed
asymmetrization of glycerol 1a,5–7 is not (R)-(+)-1c and the config-
uration originally proposed, should be reversed to (S).17
Therefore, the two main biocatalytical approaches, that is, the
enzymatic benzoylation of glycerol 1a and the Baker’s yeast biore-
duction of the hydroxyacetone monobenzoate 23,6 lead to the same
enantiomer, namely (S)-(+)-1c (Scheme 3).
recorded in ethanol {[a]D = +15.8 (c 1)} and pyridine {[a]D = +13.9
(c 1)}, and showed a positive value in both solvents for (S)-1c.
Therefore, the configuration of (+)-1-benzoyloxypropane-2,3-diol
1c prepared by the CAL-catalyzed benzoylation of glycerol 1a5–7
should be reversed from (R) to (S).
Finally, starting from [(S)-(+)-2,2-dimethyl-1,3-dioxolane-4-
methanol] 3, the complementary synthesis of enantiomerically
pure (R)-1c was achieved efficiently in two steps, that is, benzoyl-
ation and hydrolysis of the acetonide protection (63% overall yield,
Scheme 2). In order to avoid racemization in the hydrolytic step,
we performed the cleavage of the protecting group under a few
conditions described for the specific purpose16 and the use of a re-
sin with a sulfonic acid functionality (Amberlyst 15)-ethanol (95%)
system13 gave the most satisfactory results.
Enantiomerically pure (R)-1c is, at present, only available via a
chemical approach which starts from (S)-(+)-2,2-dimethyl-1,3-
dioxolane-4-methanol 3.18
4. Experimental
4.1. General
1H and 13C NMR spectra were recorded at 298 K in the indicated
The sample of (R)-1c showed a negative specific rotation
{½a 2D0
¼ ꢁ15:9 (c 1, ethanol) and ꢁ13.8 (c 1, pyridine} and a >98%
ꢀ
deuterated solvents on
a Bruker AVANCE 500 spectrometer
ee was established by the 1H NMR analysis of the corresponding
Mosher ester.
equipped with a 5 mm broadband reverse probe with field z-gradi-
O
OH
OH
bakers' yeast/glucose
CAL
Ph
O
OH
phosphate buffer (pH=6)
HO
OH
Ph
O
OH
VB, 1,4-dioxane
30 °C, 4 h
O
1a
O (S)-(+)-1c
2
Scheme 3. Biocatalytic approaches to (S)-(+)-1-benzoyloxypropane-2,3-diol 1c.

660
S. Casati et al. / Tetrahedron: Asymmetry 22 (2011) 658–661
ent operating at 500.13 MHz for 1H and 125.76 MHz for 13C. Chem-
ical shifts (d) are given as parts per million relative to the residual
solvent peak and coupling constants (J) are in Hertz. The splitting
pattern abbreviations are as follows: s, singlet; d, doublet; t, trip-
let; q, quartet; m, multiplet, and br, broad peak. Column chroma-
tography was performed on Silica Gel 60 (70–230 mesh) using
the specified eluants. Optical rotations were measured on a Per-
kin–Elmer 241 polarimeter (sodium D line at 25 °C). Melting points
were determined with a Stuart Scientific SMP3 melting point appa-
ratus and are uncorrected. The progress of the reaction was moni-
tored by analytical thin-layer chromatography (TLC) on pre-coated
glass plates (Silica Gel 60 F254-plate-Merck, Darmstadt, Germany)
and the products were visualized by UV light. The purity of all
compounds (P99%) was verified by thin layer chromatography
and NMR measurements. The optical purity of alcohols (R)-1c
and (S)-1c (>98% ee) was determined by 1H NMR analysis of its
Mosher’s ester. Elemental analyses were obtained for all interme-
diates and are within 0.4% of theoretical values. The chemicals
and solvents were obtained from Sigma–Aldrich and used without
further purification.
dichloromethane (10 mL) with stirring. After 1 h, the reaction mix-
ture was poured into water, the organic layer was separated and
the aqueous phase extracted with dichloromethane (2 ꢂ 5 mL).
After evaporation of the solvent, purification by chromatography
column on silica gel (petroleum ether/ethylacetate 8:2 and 7:3)
afforded 900 mg (3.1 mmol, 67%) of (S)-5 as a viscous liquid.
½
a 2D0
ꢀ
¼ þ6:1 (c 1, CHCl3), {lit.20
½
a 2D5
ꢀ
¼ þ6:25 (c 6.28, Et2O)}. Rf
(20% ethyl acetate/hexane) 0.2; 1H NMR (CDCl3) d 3.62 (1H, dd,
J = 5.9, 9.5 Hz, 3-CHHO), 3.67 (1H, dd, J = 4.2, 9.5 Hz, 3-CHHO),
4.21 (1H, dddd, J = 4.2, 4.9, 5.6, 5.9 Hz, 2-CHOH), 4.42–4.48 (2H,
m, part AB of ABX system, 1-CH2O), 4.61 (2H, s, OCH2Ph), 7.35–
7.39 (5H, m, OCH2Ph); 7.46 (2H, dd, J = 7.0, 7.0 Hz, m-Ph H), 7.60
(1H, t, J = 7.0, p-Ph H), 8.05 (2H, d, J = 7.0, o-Ph H); 13C NMR d
66.0 (1-C), 69.0 (2-C), 70.9 (3-C), 73.6 (OCH2Ph), 127.8 (o-PhCH),
127.9 (p-PhCH), 128.4 (m-PhCH), 128.5 (m-PhCH), 129.7 (o-PhCH),
129.9 (PhC), 133.1 (p-PhCH), 137.7 (PhC), 166.7 (CO).
4.5. Preparation of (S)-1-benzoyloxy-2,3-propanediol (S)-1c
To a solution of (S)-5 (900 mg, 3.1 mmol) in methanol, 10% Pd/C
(90 mg) was added. The reaction was put under hydrogen atmo-
sphere at room temperature for 6 h. After filtration on a Celite
pad, the residue was evaporated and purified by column chroma-
tography on silica gel (dichloromethane/methanol 95:5), affording
4.2. Preparation of (S)-1-benzyloxy-2,3-isopropylidene glycerol
(S)-4
At first, 1 g of 60% NaH in mineral oil was added to a solution of
(S)-3 (1.00 g, 7.6 mmol) in anhydrous THF (10 mL). After 10 min,
1 mL of benzyl bromide (1 mL, 8.4 mmol) was added portion wise.
The mixture was stirred for 3 h at room temperature and monitored
by TLC (petroleum ether/ethylacetate 9:1). The mixture was cau-
tiously poured in a 10% solution of ammonium chloride into water
and extracted with dichloromethane (3 ꢂ 10 mL). Evaporation of
the solvents under vacuum and purification by chromatography
column on silica gel (petroleum ether/ethylacetate 9:1) afforded
(S)-1c (500 mg, 81%) as a viscous liquid. ½a D20
¼ þ15:8 (c 1, EtOH),
ꢀ
½
a 2D0
ꢀ
¼ þ13:9 (c 1, pyridine), {lit.3
½
a 2D5
ꢀ
¼ þ13:7 (c 2, pyridine)}. Rf
(40% ethyl acetate/hexane) 0.13; 1H NMR (CDCl3) d 3.69 (1H, dd,
J = 6.0, 11.5 Hz, 3-CHHOH), 3.79 (1H, dd, J = 3.5, 11.5 Hz, 3-
CHHOH), 4.05–4.11 (1H, m, CHOH), 4.41–4.46 (2H, m, part AB of
ABX system, 1-CH2O), 7.43 (2H, dd, J = 7.0, 7.0 Hz, m-Ph H), 7.56
(1H, t, J = 7.0, p-Ph H), 8.04 (2H, d, J = 7.0, o-Ph H); 13C NMR d
63.5 (3-C), 65.7 (1-C), 70.4 (2-C), 128.4 (m-PhCH), 129.5 (o-PhCH),
129.7 (PhC), 133.3 (p-PhCH), 166.9 (CO).
1.3 g (5.8 mmol, 76%) of (S)-4 as a colorless oil. ½a D20
¼ þ21:9 (c 1,
ꢀ
CHCl3), {lit.12
½
a 2D5
ꢀ
¼ þ18:0 (neat)}. Rf (20% ethyl acetate/hexane)
4.6. Preparation of (R)-1-benzoyloxy-2,3-isopropylidene
glycerol (R)-6
0.6; 1H NMR (CDCl3) d 1.39 (3H, s, CH3), 1.45 (3H, s, CH3), 3.50
(1H, dd, J = 5.6, 9.8 Hz, 1-CHHO), 3.59 (1H, dd, J = 5.9, 9.8 Hz, 1-
CHHO), 3.77 (1H, dd, J = 6.6, 8.4 Hz, 3-CHHO), 4.09 (1H, dd, J = 6.6,
8.4 Hz, 3-CHHO), 4.33 (1H, dddd, J = 5.6, 5.9, 6.6, 6.6, 2-CHO), 4.59
(1H, d, J = 11.9 Hz, OCHHPh), 4.62 (1H, d, J = 11.9 Hz, OCHHPh),
7.34–7.38 (5H, m, OCH2Ph); 13C NMR d 25.4 (CH3), 26.8 (CH3),
66.9 (3-C), 71.1 (1-C), 73.5 (OCH2Ph), 74.8 (2-C), 109.4 (C(CH3)2),
127.7 (o-PhCH, p-PhCH), 128.4 (m-PhCH), 137.9 (PhC).
A solution of benzoyl chloride (1.0 mL, 9.0 mmol) in dichloro-
methane was added slowly to an ice-cooled solution of (S)-3
(1.00 g, 7.6 mmol) and triethylamine (2.0 mL, 15.2 mmol) in
dichloromethane (10 mL) with stirring. After 1 h, the reaction mix-
ture was poured into water, the organic layer was separated and
the aqueous phase extracted with dichloromethane (2 ꢂ 5 mL).
After evaporation of the solvent, purification by chromatography
column on silica gel (petroleum ether/ethylacetate 8:2) afforded
4.3. Preparation of (R)-1-benzyloxy-2,3-propanediol (R)-1b
1.3 g (5.3 mmol, 72%) of (R)-6 as a viscous liquid. ½a D20
¼ þ14:8 (c
ꢀ
To 1.3 g (5.8 mmol) of (S)-4 (10 mL), 1.0 g of Amberlyst 15 was
added. After 3 h at room temperature under stirring, the reaction
was filtered and the solvent removed under vacuum. Purification
by chromatography column on silica gel (petroleum ether/ethyl-
acetate 7:3) afforded 920 mg (4.9 mmol; 85%) of (R)-1b as a viscous
1, CHCl3), {lit.1a
½
a 2D5
ꢀ
¼ þ14:4 (c 1, CHCl3)}. Rf (40% ethyl acetate/
hexane) 0.73; 1H NMR (CDCl3) d 1.41 (3H, s, CH3), 1.48 (3H, s,
CH3), 3.90 (1H, dd, J = 6.6, 8.4 Hz, 3-CHHO), 4.16 (1H, dd, J = 6.6,
8.4 Hz, 3-CHHO), 4.36–4.44 (2H, m, part AB of ABX system, 1-
CH2O), 4.46–4.50 (1H, m, 2-CHO), 7.46 (2H, dd, J = 7.0, 7.0 Hz, m-
PhH), 7.54 (1H, t, J = 7.0, p-PhH), 8.08 (2H, d, J = 7.0, o-PhH); 13C
NMR d 25.4 (CH3), 26.8 (CH3), 65.1 (1-C), 66.4 (3-C), 73.7 (2-C),
109.9 (C(CH3)2), 128.4 (m-PhCH), 129.7 (o-PhCH), 130.6 (PhC),
133.2 (p-PhCH), 166.4 (CO).
liquid. ½a 2D0
ꢀ
¼ þ5:9 (c 1, CHCl3), {lit.19
½
a 2D5
ꢀ
¼ þ5:6 (c 20, CHCl3)}. Rf
(40% ethyl acetate/hexane) 0.13; 1H NMR (CDCl3) d 3.55 (1H, dd,
J = 6.3, 10.0 Hz, 3-CHHOH), 3.59 (1H, dd, J = 4.2, 10.0 Hz, 3-CHHOH),
3.63 (1H, dd, J = 5.9, 11.5 Hz, 1-CHHOPh), 3.71 (1H, dd, J = 3.8,
11.5 Hz, 1-CHHOPh), 3.91 (1H, dddd, J = 3.8, 4.2, 5.9, 6.3 Hz, 2-
CHOH), 4.57 (2H, s, OCH2Ph), 7.31–7.39 (5H, m, OCH2Ph); 13C
NMR d 64.1 (3-C), 70.7 (2-C), 71.8 (1-C), 73.6 (OCH2Ph) 127.8 (o-
PhCH), 127.9 (p-PhCH), 128.5 (m-PhCH), 137.7 (PhC).
4.7. Preparation of (R)-1-benzoyloxy-2,3-propanediol (R)-1c
To 1.3 g (5.3 mmol) of (R)-6 in methanol (10 mL) was added
1.0 g of Amberlyst 15. After 3 h at room temperature under stirring,
the reaction was filtered and the solvent removed under vacuum.
Purification by chromatography column on silica gel (petroleum
ether/ethylacetate 6:4) afforded 900 mg (4.6 mmol; 87%) of (R)-
4.4. Preparation of (S)-1-benzoyloxy -3-benzyloxy-2-propanol
(S)-5
A solution of benzoyl chloride (0.7 mL, 5.6 mmol) in dichloro-
methane was added slowly to an ice-cooled solution of (R)-1b
(920 mg, 4.7 mmol) and triethylamine (1.3 mL, 9.4 mmol) in
1c as a viscous liquid. ½a D20
ꢀ
¼ ꢁ15:9 (c 1, EtOH), ½a D20
¼ ꢁ13:8 (c
ꢀ
1, pyridine), {lit.18
½
a 2D5
ꢀ
¼ ꢁ13:3 (c 1.3, pyridine)}. Rf (40% ethyl ace-
tate/hexane) 0.13; 1H NMR (CDCl3) d 3.69 (1H, dd, J = 6.0, 11.5 Hz,

S. Casati et al. / Tetrahedron: Asymmetry 22 (2011) 658–661
661
3-CHHOH), 3.79 (1H, dd, J = 3.5, 11.5 Hz, 3-CHHOH), 4.05–4.11 (1H,
References
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8.04 (2H, d, J = 7.0, o-Ph H); 13C NMR d 63.5 (3-C), 65.7 (1-C),
70.4 (2-C), 128.4 (m-PhCH), 129.5 (o-PhCH), 129.7 (PhC), 133.3
(p-PhCH), 166.9 (CO).
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17. Kato et al. (Refs. 5–7) assigned an (R)-configuration to (+)-1c referring to the
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To
a
stirred solution of alcohol (R)-1c or (S)-1c (20 mg,
-methoxy- -trifluoromethylphenyl acetic acid
0.1 mmol), (R)-
a
a
(24 mg, 0.106 mmol), and 4-dimethylaminopyridine (2 mg) in dry
CH2Cl2 (3 mL) was added dropwise a solution of DCC (22 mg,
0.106 mmol) in CH2Cl2 (2 mL) at 0 °C under a nitrogen atmosphere
and stirred at the same temperature for 30 min. Then the reaction
mixture was brought to room temperature and stirred for 12 h. The
reaction mixture was diluted with CH2Cl2 (40 mL), washed with
saturated aqueous NaHCO3 solution followed by brine, dried over
anhydrous Na2SO4, and concentrated under reduced pressure.
The crude product was purified by silica gel chromatography using
ethyl acetate/hexane (4:96) to give the Mosher’s ester in 87% yield.
4.8.1. Mosher’s ester of alcohol (R)-1c
Colorless oil; 1H NMR (CDCl3) representative signals d 3.47 (s,
3H), 3.49 (s, 3H), 3.47 (s, 3H), 4.47 (1H, dd, J = 4.2, 12.2 Hz, 3-
CHHO), 4.49 (1H, dd, J = 5.9, 11.0 Hz, 1-CHHO), 4.59 (1H, dd,
J = 3.5, 11.0 Hz, 1-CHHO), 4.76 (1H, dd, J = 3.5, 12.2 Hz, 3-CHHO),
5.75 (1H, dddd, J = 3.5, 3.5, 4.2, 5.9, 2-CHO).
18. Compound (R)-1c has been prepared by another enzymatic approach; see:
Breitgoff, D.; Laumen, K.; Schneider, M. P. J. Chem. Soc., Chem. Commun. 1986,
1523–1524. This biocatalytic protocol starts with the asymmetrization of the
1,3-diacetate of 2-benzyloxyglycerol via lipase-catalyzed hydrolysis. This
allowed the preparation of the corresponding monoacetate (53% conversion,
75% yield of purified product) which was transformed into (R)-(ꢁ)-1c in three
additional steps (yields not reported).
19. Sawant, R. T.; Waghmode, S. B. Tetrahedron 2010, 66, 2010–2014.
20. Noe, C. R.; Knollmüller, M.; Miculka, C.; Dungler, K.; Wagner, E.; Ettmayer, P.
Chem. Ber. 1994, 127, 887–892.
4.8.2. Mosher’s ester of alcohol (S)-1c
Colorless oil; 1H NMR (CDCl3) representative signals d 3.41 (s,
3H), 3.52 (s, 3H), 3.47 (s, 3H), 4.39 (1H, dd, J = 4.2, 12.2 Hz, 3-
CHHO), 4.42 (1H, dd, J = 5.9, 11.0 Hz, 1-CHHO), 4.54 (1H, dd,
J = 3.5, 11.0 Hz, 1-CHHO), 4.81 (1H, dd, J = 3.5, 12.2 Hz, 3-CHHO),
5.70 (1H, dddd, J = 3.5, 3.5, 4.2, 5.9, 2-CHO).
Acknowledgment
This work was financially supported by Università degli Studi di
Milano (Fondi FIRST).