Optical resolution of racemic alcohols via diastereoisomeric supramolecular compound formation with O,O'-dibenzoyl-(2R,3R)-tartaric acid

Article abstract of DOI:10.1016/S0040-4020(00)00776-6

O,O'-Dibenzoyl-(2R,3R)-tartaric acid (DBTA) forms a hydrogen bonded supramolecular compound with alcohols. The supra-molecular compound formation is enantioselective for a large number of chiral alcohols, therefore DBTA can be used as resolving agent, also for compounds having no basic group. The condition of the complex formation is that the guest molecule should contain a proton donating group and a fitting aliphatic chain or cycloalkane ring. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00776-6

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 8355±8359
Optical Resolution of Racemic Alcohols via Diastereoisomeric
Supramolecular Compound Formation with
0
O,O -Dibenzoyl-(2R,3R)-tartaric Acid
a
Csaba Kassai, Zolt a n Juvancz, J o zsef B a lint, Elem e r Fogassy and D a vid Kozma
b
a
a
a,*
a
Department of Organic Chemical Technology, Budapest University of Technology and Economics, H-1521 Budapest, M uÍ egyetem rkp. 3,
P.O. Box 91, Hungary
b
VITUKI Plc., H-1095, Budapest, Kvassay J. u. 1, Hungary
Received 22 May 2000; revised 8 August 2000; accepted 23 August 2000
0
AbstractÐO,O -Dibenzoyl-(2R,3R)-tartaric acid (DBTA) forms a hydrogen bonded supramolecular compound with alcohols. The supra-
molecular compound formation is enantioselective for a large number of chiral alcohols, therefore DBTA can be used as resolving agent, also
for compounds having no basic group. The condition of the complex formation is that the guest molecule should contain a proton donating
group and a ®tting aliphatic chain or cycloalkane ring. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
compounds without basic character. This can be interesting
not only from a theoretical point of view, but also from a
practical viewpoint since TA and DBTA are the two most
frequently used, widely available and inexpensive acidic
resolving agents.
When a racemate contains a basic or an acidic group, its
optical resolution can always be accomplished by dia-
stereoisomeric salt formation as among the large number
of basic or acidic resolving agents, usually at least one
1
,2
effective resolving agent can be found.
Results and Discussion
The optical resolution of alcohols is more complicated. The
enantiomers can be separated after derivatization (dia-
stereoisomeric ester, or a diastereoisomeric salt) or, in one
step, by complex formation. The one-step process would be
the most practical way but until now a generally applicable,
easily available complex forming resolving agent has not
been found. Several research groups have tried to ®nd
complex forming resolving agents, usually by derivatizing
The stability of a supramolecular compound is determined
by the number of the weak interactions. The good complex
forming ability of DBTA arises from a number of factors.
Although the carboxylic acid groups of DBTA can donate
protons for hydrogen bonding, it can also behave as a proton
acceptor due to the 8 oxygen atoms it contains. The benzoyl
groups can take part in hydrophobic interactions while the
other part of the molecule contains polar hydrophilic
groups.
3
±12
the salt forming resolving agents,
but these resolving
agents can only be applied for the resolution of a small
number of racemates on a laboratory scale and unfortunately
they are not available in bulk quantities.
Coordinative metal complexes of DBTA are also known to
1
2
have been used for optical resolution, but the diastereo-
isomeric supramolecular compound forming properties of
DBTA have not yet been investigated.
Recently we have observed that the basic (N-alkyl)-pipeco-
lic acid anilides can form supramolecular compounds with
natural (2R,3R)-tartaric acid (TA) and with its benzoyl
0
13
derivative O,O -dibenzoyl-(2R,3R)-tartaric acid (DBTA).
Supramolecular compound forming properties of TA and
DBTA were pre-tested with ®ve chiral alcohols and it was
found that the resolution is only possible with DBTA, while
TA did not interact with those alcohols. The preliminary
experiments showed a more ef®cient enantiomeric separa-
tion using DBTA monohydrate than anhydrous DBTA, so
Based on this observation we have assumed that TA and
DBTA may also be used for the resolution of racemic
0
Keywords: O,O -dibenzoyl-(2R,3R)-tartaric acid; (2R,3R)-tartaric acid;
racemic compounds.
1
6
subsequently that was used. Among the tested racemic
alcohols the resolution of menthol showed the highest
* Corresponding author. Tel.: 1361-463-1414; fax: 1361-463-3648;
e-mail: david@oct.bme.hu
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00776-6

8
356
C. Kassai et al. / Tetrahedron 56 (2000) 8355±8359
1
4
Table 1. Summary of the resolution results (The yield is related to the half amount of the racemate. Sˆe.e.£ yield. The con®gurations of the main isomers
1
were identi®ed by optical rotatory measurements. )
5
#
The con®guration of the enriched enantiomer is shown in the table.
stereoselectivity, so for the systematic investigation
alcohols with related structures were selected.
amount of the unreacted enantiomer remains in the mother
liquor). The formation of the supramolecular compound by
recrystallization of the solid phase starts on the solid±liquid
interface and at room temperature, without stirring last
about 1 week.
During optical resolutions, the diastereoisomers are gener-
ally separated by fractional crystallization which usually
requires solvents. The selection of the appropriate solvents
is not only a time- and labour-consuming process but the
results with different solvents are hardly comparable. We
developed a generally applicable process for the separation
of diastereoisomeric supramolecular compounds by the use
of hexane as semi-inert solvent. Hexane dissolves the
alcohols but it does not dissolve the DBTA-monohydrate
and the DBTA-alcohol supramolecular compound. The
applied process is simple, generally applicable and the
results are comparable.
After ®ltration, the alchol enriched in one enantiomer can be
obtained from the mother liquor and the other one from the
solid compound. The enantiomericaly enriched alcohol
which was a part of the supramolecular compound can be
recovered by distillation or sublimation.
The results of 22 experiments are summarised in Table 1
(the homologous compounds are listed one after the other).
By the comparison of the resolution results of the homo-
logous compounds the following conclusions can be drawn:
The alcohol was dissolved in hexane and DBTA-mono-
hydrate was suspended in this solution (one molar equiva-
lent of DBTA-monohydrate was reacted with two molar
equivalents of alcohol because we supposed that the molar
ratio in the supramolecular compound is 1:1, and half the
1. Supramolecular compound formation in trans-selective
in the case of 2-substituted cyclohexanols (e.g. menthol
(18) forms a supermolecular compound while iso-
menthol (19) does not). Supramolecular compound

C. Kassai et al. / Tetrahedron 56 (2000) 8355±8359
8357
formation is also trans selective for the achiral 4-alkyl-
cyclohexanols.
Preparation of trans-2-chloro-cyclohexanol (10) from
cyclohexene-oxide
1
7
2
. Among aliphatic secondary alcohols, 2-pentanols (3,4)
form enantioselective supramolecular compounds with
DBTA.
To a cooled and stirred 37% aqueous HCl solution (17.8 ml,
0.153 mol) was added dropwise cyclohexene-oxide (5.00 g,
51 mmol). The solution was allowed to warm up to room
temperature and was extracted with 3£20 ml of CH Cl .
3
. The 2-alkyl-cyclohexanols having a group larger than
isopropyl do not interact with DBTA (20).
2
2
4
. In the case of trans-2-alkoxy-cyclohexanols the enantio-
selectivity and the con®guration of the alcohol in the
supramolecular compound also depends on the size of
the alkoxy group (13±17).
The organic phase was washed with 2£20 ml of saturated
aqueous NaCl solution, dried over MgSO , ®ltered and the
4
solvent was evaporated. The residue was puri®ed by distil-
lation (83±868C/15 Hgmm). Yield 5.52 g (80%). IR [cm ],
2
1
1
3358; 2939; 2861; 1450; 1073. H NMR, 1.25±1.45 (m,
5. The enantioselectivity in the case of 2-alkyl-cyclo-
hexanols depends on the size of the alkyl group. For
3H); 1.55±1.85 (m, 3H); 2.08±2.18 (m, 1H), 2.18±2.30
(m, 1H); 2.90±2.97 (m, 1H); 3.45±3.60 (m, 1H); 3.65±
2-methyl- and 2-ethyl-cyclohexanols the S,S-trans
isomer was incorporated into the supramolecular
1
3
3.82 (m, 1H). C NMR, 23.6, 25.2, 32.9, 34.8, 66.7, 74.7.
Anal. calcd for C H ClO: C 53.54, H 8.24, Cl 26.34, found:
C 53.61, H 8.21.
compound while menthol (18) incorporated with the
opposite con®guration.
6
11
1
7
6
. trans-2-Halogen-cyclohexanols form supramolecular
compounds of S,S con®guration (10±12). The
enantioselectivity increases with the size of the halogen
atom.
Preparation of trans-2-bromo-cyclohexanol (11) from
cyclohexene-oxide
To a cooled and stirred 48% aqueous HBr solution (38 ml,
0
5
.153 mol) was added dropwise cyclohexene-oxide (5.00 g,
1 mmol). The solution was allowed to warm up to room
temperature and was extracted with 3£20 ml of CH Cl .
2
2
Experimental
The organic phase was washed with 2£20 ml of saturated
aqueous NaCl solution, dried over MgSO , ®ltered and the
4
A Hewlett±Packard HP 5890/II instrument with FID
detector was used for GC analysis. The column used was
a 12 m£0.100 mm I.D. fused silica open tubular column
coated with ChirasilDex chiral stationary phase at
solvent was evaporated. The residue was puri®ed by distil-
lation (93±948C/15 Hgmm). Yield 7.36 g (80%). IR [cm ],
21
1
3
3
(
3
385; 2938; 2860; 1449; 1072. H NMR, 1.18±1.48 (m,
H); 1.65±1.95 (m, 3H); 2.08±2.20 (m, 1H), 2.28±2.40
m, 1H); 2.55±2.60 (m, 1H); 3.55±3.67 (m, 1H); 3.85±
0.15 mm ®lm thickness. The stationary phase was a methyl-
silicone polymer substituted with permethylated b-cyclo-
13
.98 (m, 1H). C NMR, 23.7, 26.2, 33.4, 35.8, 61.0, 74.7.
Anal. calcd for C H BrO: C 40.25, H 6.19, Br 44.62, found:
1
dextrin via spacer. H was used as carrier gas with 1 ml/
8
2
6
11
min speed. The injection mode was split (1:160). The analy-
sis temperature was adjusted to the volatility and selectivity
of analytes. Several analytes were analysed in free form, but
a few samples required derivatization with TFAA according
C 40.17, H 6.24.
Preparation of trans-2-iodo-cyclohexanol (12) from
cyclohexene-oxide
1
9
to standard procedure. Compounds 10±12 were analysed
as acetyl derivatives, the others without derivatization
between 323±373 K. The IR measurements were made by
a Perkin±Elmer FT-IR 1600. The NMR spectra were taken
on a Bruker AC 250 FT-NMR. All spectra were measured in
To a stirred aqueous KI (25.4 g, 0.153 mol/50 ml H O) solu-
2
tion was added cyclohexene-oxide (5.00 g, 51 mmol). To
the cooled KI-solution was added dropwise aqueous
H SO solution (4 ml of 98% H SO /20 ml H O). The solu-
2
4
2
4
2
CDCl solution and chemical shift values are expressed in
3
1
ppm from TMS (0.0 ppm) in the case of C NMR from
3
tion was allowed to warm up to room temperature and was
extracted with 4£20 ml of CH Cl . The organic phase was
2
2
CDCl (77.0 ppm) as internal standard on d scale. All
3
chemicals were purchased from Aldrich except 10±17
which were synthesized by known organic methods.
washed with 3£20 ml of saturated aqueous NaCl solution,
2
0
dried over MgSO
The residue was puri®ed by distillation (107±1118C/
, ®ltered and the solvent was evaporated.
4
2
1
1
5 Hgmm). Yield 10.21 g (81%). mpˆ438C, IR [cm ],
1
General procedure for preparing DBTA-alcohol supra-
molecular compounds
KBr, 3405; 2933; 2853; 1447; 1066. H NMR, 1.20±1.60
(m, 4H); 1.80±1.92 (m, 1H); 1.95±2.20 (m, 2H), 2.30
(
3.98±4.10 (m, 1H). C NMR, 24.3, 27.8, 33.6, 38.4, 43.1,
broad s, 1H), 2.35±2.50 (m, 1H); 3.60±3.72 (m, 1H);
1
3
50 mmol of alcohol was dissolved in 20±40 ml of hexane
and in this solution 25 mmol of DBTA monohydrate was
suspended. After 1 week standing at room temperature the
solid supramolecular compound was ®ltered off and dried
in air. The solid supramolecular compound was dissolved
75.7. Anal. calcd for C
found: C 31.92, H 4.85.
H11IO: C 31.88, H 4.90, I 56.14,
6
Preparation of trans-2-methoxy-cyclohexanol (13) from
cyclohexene-oxide
in aqueous Na CO3 solution, extracted by 3£20 ml of
2
CH Cl . The organic phase was evaporated and the
2
2
alcohol component was puri®ed by distillation. The
mother liquor was distilled, the ®rst fraction was hexane,
the second fraction was the unreacted alcohol enantiomeric
mixture.
Cyclohexene-oxide (5.00 g, 51 mmol) was dissolved in
15 ml of MeOH then 1.00 g (19 mmol) of NaOMe was
added. The solution was re¯uxed for 6 h, then 30 ml of
H O was added, extracted with 3£10 ml of CH Cl . The
2
2
2

8
358
C. Kassai et al. / Tetrahedron 56 (2000) 8355±8359
organic phase was dried over MgSO , the solvents were
4
and was added cyclohexene-oxide (5.00 g, 51 mmol). The
solution was re¯uxed for 5 h then 60 ml of H O was added,
evaporated and the residue was puri®ed by distillation
(
2
2
80±828C/15 Hgmm). Yield 5.10 g (77%). IR [cm ],
1
extracted with 3£50 ml of CH Cl . The organic phase was
2
2
1
3
4
(
440; 2933; 2861; 1452; 1102. H NMR, 0.95±1.40 (m,
H); 1.65±1.80 (m, 2H); 1.90±2.20 (m, 1H), 2.85±3.00
dried over MgSO , the solvents were evaporated and the
4
residue was puri®ed by distillation (107±1088C/
15 Hgmm). Yield 7.10 g (81%). IR [cm ], 3440; 2933;
1
3
m, 1H); 3.12 (s, 1H); 3.42 (s, 4H). C NMR, 23.6, 23.7,
21
1
2863; 1451; 1101. H NMR, 0.80±1.00 (m, 3H); 1.00±
2
6
8.8, 31.9, 55.9, 73.0, 84.6. Anal. calcd for C H O : C
7
4.58, H 10.84, found: C 64.49, H 10.79.
14
2
1.45 (m, 6H); 1.45±1.80 (m, 4H), 1.85±2.15 (m, 2H);
.85±3.07 (m, 1H); 3.14 (s, 1H); 3.20±3.49 (m, 2H);
2
1
3
Preparation of trans-2-ethoxy-cyclohexanol (14) from
cyclohexene-oxide
3.52±3.72 (m, 1H). C NMR, 13.5, 19.0, 23.6, 23.9, 28.8,
31.8, 31.9, 68.2, 73.3, 83.2. Anal. calcd for C10 : C
H O
20 2
6
9.72, H 11.70, found: C 69.77, H 11.65.
Cyclohexene-oxide (5.00 g, 51 mmol) was dissolved in
15 ml of EtOH and into this solution 1.00 g (15 mmol) of
NaOEt was added. The solution was re¯uxed for 6 h, then
Acknowledgements
3
0 ml of H O was added, extracted with 3£10 ml of CH Cl .
2
2
2
The organic phase was dried over MgSO , the solvents were
4
The authors are grateful for ®nancial support to OTKA
Foundation (grant numbers: T29251 (E. F.), D32705
(J. B.), T31711 (D. K.)), C. K. for the J. Varga Foundation.
evaporated and the residue was puri®ed by distillation
(
2
1
82±848C/15 Hgmm). Yield 5.64 g (77%). IR [cm ],
1
3446; 2973; 2933; 2863; 1450; 1107. H NMR, 1.05±1.40
(
(
m, 7H); 1.60±1.85 (m, 2H); 1.93±2.20 (m, 2H), 2.95±3.10
m, 1H); 3.17 (s, 1H); 3.33±3.55 (m, 2H); 3.63±3.85 (m,
References
1
H). C NMR, 15.3, 23.7, 24.2, 29.1, 32.0, 63.8, 73.2, 83.1.
3
1
Anal. calcd for C H O : C 66.63, H 11.18, found: C 66.58,
H 11.24.
8
16
2
1. Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic
Compounds; Wiley: New York, 1994.
2
. Newman, P. Optimal Resolution Procedures for Chemical
Preparation of trans-2-isopropoxy-cyclohexanol (15)
from cyclohexene-oxide
Compounds; Optical Resolution Information Center, Manhattan
College, N.Y. Riverdale 1978±84.
3
. Seebach, D.; Beck, A. K.; Imwinkelried, R.; Roggo, S.;
Na (1.20 g, 52 mmol) was dissolved in 30 ml of iPrOH and
was added cyclohexene-oxide (5.00 g, 51 mmol). The solu-
tion was re¯uxed for 12 h then 30 ml of H O was added,
Wonnacott, A. Helv. Chim. Acta 1987, 70, 954.
4. Toda, F. Top. Curr. Chem. 1987, 140, 44.
2
5. Weber, E.; Wimmer, C.; Llamas-Saiz, A. L.; Forces-Forces, C.
J. Chem. Soc., Chem. Commun. 1992, 733.
extracted with 2£30 ml of CH Cl . The organic phase was
2
2
dried over MgSO , solvents were evaporated and the residue
4
6. Toda, F.; Tanaka, K.; Stein, Z.; Goldberg, I. J. Chem. Soc.,
Perkin Trans. 2 1993, 2359.
was puri®ed by distillation (96±1048C/15 Hgmm). Yield
2
.93 g (49%). IR [cm ], 3446; 2970; 2933; 2862; 1451;
1
3
1
1
3
3
1
7. Toda, F.; Tohi, Y. J. Chem. Soc., Chem. Commun. 1993, 1238.
8. Toda, F.; Tanaka, K.; Watanabe, M.; Abe, T.; Harada, N.
Tetrahedron 1995, 6, 1495.
9. Korkas, P. P.; Weber, E.; N a ray-Szab o , G. J. Chem. Soc., Chem.
Commun. 1995, 2229.
1
075. H NMR, 1.05±1.40 (m, 10H); 1.65±1.80 (m, 2H);
.90±2.15 (m, 2H), 2.90±3.20 (m, 2H); 3.30±3.47 (s, 1H);
1
3
.67±3.85 (m, 1H). C NMR, 21.9, 23.4, 23.7, 24.0, 30.0,
1.8, 69.2, 73.2, 80.9. Anal. calcd for C H O : C 68.31, H
1.47, found: C 68.22, H 11.40.
9
18
2
10. Tsunoda, T.; Kaku, H.; Nagaku, M.; Okuyama, E. Tetrahedron
Lett. 1997, 38, 7759.
Preparation of trans-2-propoxy-cyclohexanol (16) from
cyclohexene-oxide
11. Farina, A.; Meille, S. V.; Messina, M. T.; Metrangolo, P.;
Resnati, G.; Vecchio, G. Angew. Chem., Int. Ed. Engl. 1999, 38,
2433.
12. Mravik, A.; B oÈ cskei, Zs.; Katona, Z.; Markovits, I.; Fogassy,
E. Angew. Chem., Int. Ed. Engl. 1997, 36, 1534.
Na (1.40 g, 61 mmol) was dissolved in 30 ml of PrOH and
was added cyclohexene-oxide (5.00 g, 51 mmol). The
solvent was re¯uxed for 6 h and 60 ml of H O was added,
Â
13. Nem a k, K.; Acs, M.; J a szay, Zs.; Kozma, D.; Fogassy, F.
2
extracted with 3£50 ml of CH Cl . The organic phase was
Tetrahedron 1996, 52, 1637.
14. Fogassy, E.; Lopata, A.; Faigl, F.; Acs, M.; Darvas, F.; T oÍ ke,
2
2
Â
dried over MgSO , the solvents were evaporated and the
4
residue was puri®ed by distillation (73±768C/15 Hgmm).
Yield 3.85 g (48%). IR [cm ], 3424; 2935; 2861; 1451;
L. Tetrahedron Lett. 1980, 21, 647.
25
2
1
15. (R)-2-pentanol (3), [a] ˆ213 (cˆ1; neat), measured:
D
1
25
D
1
1
2
1
086. H NMR, 0.80±1.00 (m, 3H); 1.00±1.40 (m, 4H);
.45±1.80 (m, 4H), 1.90±2.20 (m, 2H); 2.91 (s, 1H);
.95±3.08 (m, 1H); 3.20±3.50 (m, 2H); 3.50±3.70 (m,
[a] ˆ22.555 (cˆ1; neat), Craine, L. E.; Bicknell, L. K.;
Mailloux, R. C.; Mark, J. P.; Mitchell, S. A. J. Org. Chem. 1993,
2
0
58, 1251; (R)-4-methyl-2-pentanol (4), [a] ˆ234.22 (cˆ1; neat),
D
1
3
20
D
H). C NMR, 10.1, 22.9, 23.5, 23.8, 28.8, 31.7, 70.0,
measured: [a] ˆ29.513 (cˆ1; neat), Kenyon, J.; Strauss, H. E.
73.1, 83.0. Anal. calcd for C H O : C 68.31, H 11.47,
found: C 68.25, H 11.43.
J. Chem. Soc. 1949, 2153; (S)-Tetrahydrofurfuryl alcohol (9),
9
18
2
2
0
20
D
[a] ˆ117 (cˆ1; CHCl3), measured: [a] ˆ10.10 (cˆ1;
D
CHCl
3
), Balfe, Michael P.; Irwin, M.; Kenyon, J. J. Chem. Soc.
2
0
Preparation of trans-2-butoxy-cyclohexanol (17) from
cyclohexene-oxide
1941, 312; (1R,2R)-trans-2-chloro-cyclohexanol (10), [a] ˆ
D
2
D
0
232.7 (cˆ2; CH
2
Cl
2
), measured: [a]
ˆ112.4 (cˆ2; CH
2 2
Cl ),
2
D
0
(
CH
1R,2R)-trans-2-bromo-cyclohexanol (11), [a]
ˆ233.2 (cˆ2;
2
0
Na (1.20 g, 52 mmol) was dissolved in 30 ml of n-BuOH
2
Cl
2
), measured: [a]
D
ˆ118.6 (cˆ2; CH
2 2
Cl ), (1R,2R)-trans-

C. Kassai et al. / Tetrahedron 56 (2000) 8355±8359
8359
2
D
0
20
D
ethoxy-cyclohexanol (14), [a] ˆnegative, measured: [a] ˆ
(cˆ1.21; CHCl ), Fukuzawa, T.; Hashimoto, T. Tetrahedron
3
2
41.2 (cˆ2; CH
2
Cl
ˆnegative, measured: [a]
trans-isopropoxy-cyclohexanol (15), [a] ˆ285.6 (cˆ2; CH Cl ),
2
), (1R,2R)-trans-propoxy-cyclohexanol (16),
Asymmetry 1993, 4, 2323.
16. Kozma, D.; B oÈ cskei, Zs.; Kassai, Cs.; Simon, K.; Fogassy, E.
J. Chem. Soc., Chem. Commun. 1996, 753.
2
D
0
20
[
a]
D
ˆ138.7 (cˆ2; CH
2
Cl
2
), (1R,2R)-
2
0
D
2
2
2
D
0
measured: [a]
Wasserthal, P. Synthesis 1990, 12, 1137; (1S,2S)-trans-2-iodo-
ˆ214.0 (cˆ2; CH
2
Cl
2
), Hoenig, H.; Seufer-
17. Kassai, C.; Balint, J.; Juvancz, Z.; Fogassy, E.; Kozma, D.
Synt. Comm., accepted for publication
2
D
3
cyclohexanol (12), [a] ˆ133.1 (cˆ2.5; CHCl ), measured:
18. Schurig, V.; Juvancz, Z.; Nicholson, G. J.; Schmalzing, D.
HRC & CC 1991, 14, 58.
3
2
D
3
[
Tetrahedron Asymmetry 1996, 7, 1649; (1R,2S,5R)-(2)-Menthol
a]
ˆ122.9 Fukuzawa, T.; Shimoji, Y. Hashimoto, T.
19. Knapp, D. R. Handbook of Analytical Derivatization
Reactions, Wiley: New York, 1979.
2
D
0
20
D
( ˆ250 (cˆ10; EtOH), measured: [a]
EtOH), CAS: [2216-51-5]; (S)-2-cyclohexene-1-ol (22),
18) [a]
ˆ241.6 (cˆ10;
20. Organikum, Organisch-chemisches Grundpraktikum; Schwetlick,
K.; Ed.; VEB Deutcher Verlag der Wissenschaften: Berlin, 1973.
2
D
0
20
D
[
a]
ˆ1130.6 (cˆ1.21; CHCl ), measured: [a] ˆ226.9
3