Hydroxynitrile lyase-catalyzed addition of HCN to 4-substituted cyclohexanones: Stereoselective preparation of tetronic acids

Article abstract of DOI:10.1139/v02-087

The addition of HCN to 4-alkylcyclohexanones 1 to give cyanohydrins 2 is strongly catalyzed by hydroxynitrile lyases (HNLs). With PaHNL, from bitter almond, trans-addition occurs almost exclusively, yielding trans-2. With MeHNL, from cassava, cis-addition

Full text of DOI:10.1139/v02-087

671
Hydroxynitrile lyase-catalyzed addition of HCN to
4-substituted cyclohexanones: stereoselective
preparation of tetronic acids
Franz Effenberger, Jürgen Roos, Christoph Kobler, and Holger Bühler
Abstract: The addition of HCN to 4-alkylcyclohexanones 1 to give cyanohydrins 2 is strongly catalyzed by hydroxy-
nitrile lyases (HNLs). With PaHNL, from bitter almond, trans-addition occurs almost exclusively, yielding trans-2.
With MeHNL, from cassava, cis-addition is preferred to give cis-2. cis-Selectivity is nearly quantitative, especially
for cyclohexanones with larger 4-substituents. Comparable results with respect to the stereoselectivity were observed
in the HNL-catalyzed addition of HCN to 4-alkoxycyclohexanones 3a–g. In contrast, the stereoselectivity in the HNL-
catalyzed addition to 4-alkanoyloxycyclohexanones 3h–k is very poor. The transformation of cis-4-propylcyclohexanone
cyanohydrin (2c) into the corresponding cis-spirotetronic acid 7 occurs without any isomerization.
Key words: enzyme, hydroxynitrile lyase, cyclohexanones, cyanohydrins, cis/trans-stereoselectivity.
Résumé : L’addition du HCN sur les 4-alkylcyclohexanones (1) conduisant à la formation de cyanohydrines (2) est
fortement catalysée par les lyases d’hydroxynitriles (« HNL »). Sous l’influence d’une PaHNL obtenue à partir de
l’amande amère, l’addition se fait pratiquement exclusivement de façon trans, conduisant aux trans-2. Avec une
MeHNL tirée de cassava, l’addition se fait préférentiellement de façon cis pour conduire aux cis-2. Dans les cas de
cyclohexanones portant des substituants encombrants en position 4, la sélectivité cis est pratiquement quantitative.
Des résultats de stéréosélectivités comparables sont aussi obtenus lors de l’addition de HCN, catalysée par une lyase
d’hydroxynitrile, aux 4-alcoxycyclohexanones (3a-g). Par opposition, la stéréosélectivité de l’addition de HCN, cata-
lysée par une lyase d’hydroxynitrile, sur les 4-alcanoyloxycyclohexanones (3h-k) est très faible. La transformation de
la cyanohydrine de la cis-4-propylcyclohexanone (2c) en acide cis-spirotétronique correspondant (7) se réalise sans épi-
mérisation.
Mots clés : enzyme, lyase d’hydroxynitrile, cyclohexanones, cyanohydrines, stéréosélectivité cis/trans.
[Traduit par la Rédaction] Effenberger et al. 679
Introduction
mixture of isomeric tetronic acids had to be separated by
crystallization. This procedure is not only time-consuming
but also the accumulation of the non-desired isomer is disad-
vantageous.
In this paper, we report on the enzyme-catalyzed addition
of HCN to 4-substituted cyclohexanones, which stereoselec-
tively yields the corresponding cis- or trans-cyanohydrins.
Hydroxynitrile lyases (HNLs) have been applied as bio-
catalysts. By using PaHNL from bitter almond (Prunus
amygdalus) trans isomers are preferentially formed, while
with MeHNL from cassava (Manihot esculenta) cis isomers
are the major products.
Tetronic acids C derived from 1-hydroxy-4-alkoxycyclo-
hexane-1-carboxylic acids are of particular interest as herbicides
and insecticides (1). The simplest approach to hydroxycar-
boxylic acids of this type would be the hydrolysis of cyano-
hydrins B accessible from the corresponding 4-substituted
cyclohexanones A (Chart 1). The common chemical addition
of HCN to 4-substituted cyclohexanones results in a
cis/trans-isomeric mixture of cyanohydrins B, and the
tetronic acids thus obtained would also be cis/trans isomers.
Since the different stereoisomers of tetronic acids C reveal
very distinct biological activities (1), the exclusive stereo-
selective preparation of one isomer, cis or trans, of 4-
substituted cyclohexanone cyanohydrins B is an important
target. Until now this could not be realized, and therefore the
In a previous communication (2), a mainly mechanistic ex-
planation of this unexpected cis/trans-selectivity is described
and interpreted based on the X-ray crystal structure of the
MeHNL (3), while the synthetic potential of the reaction is
Received 12 February 2002. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 29 May 2002.
Dedicated to Professor J. Bryan Jones — a good friend and an excellent scientist.
F. Effenberger,1 J. Roos,2 C. Kobler,3 and H. Bühler.4 Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55,
D-70569 Stuttgart, Germany.
1Corresponding author (e-mail: franz.effenberger@po.uni-stuttgart.de).
2Taken in part from Ph.D. thesis. Universität Stuttgart, Germany. January 1999.
3Taken from Diplomarbeit. Universität Stuttgart, Germany. September 2000.
4Taken in part from Ph.D. thesis. Universität Stuttgart, Germany. November 2000.
Can. J. Chem. 80: 671–679 (2002)
DOI: 10.1139/V02-087
© 2002 NRC Canada

672
Can. J. Chem. Vol. 80, 2002
Table 1. Formation of 4-alkylcyclohexanone cyanohydrins 2 by (S)-MeHNL- and (R)-PaHNL-catalyzed addition of HCN to
4-substituted cyclohexanones 1.
(S)-MeHNL
(R)-PaHNL
Chemical addition
t
Conv.
(%)
cis:trans
(%)
t
Conv.
(%)
cis:trans
(%)
Conv.
(%)
cis:trans
(%)
Substrate
(h)
(h)
1.5
22
31
22
216
24
3:97
2:98
2:98
1:99
10:90
1:99
4:96
4
0.5
<1
<1
2
1a
1b
1c
1d
1e
1f
2
5
5
5
3
9
3
80
quant
93
quant
82
99
35:65
74:26
96:4
97:3
99:1
98:2
99:1
99
99
83
94
50
99
71
17:83
16:84
15:85
13:87
13:87
11:89
9:91
2.5
28
1g
95
264
Chart 1.
Scheme 1.
OH
O
O
+
HCN
R
CN
+
HCN
RO
RO
1
A
B
iPr2O, rt
(S)-MeHNL
(R)-PaHNL
cis/trans cyanohydrins
CN
OH
O
OH
CN
R
R
O
trans-2
cis-2
RO
4-O2NC6H4COCl
pyridine/DMAP
OH
for 2f
R=
1, 2
C
a
b
c
d
e
f
Me
cis/trans tetronic acids
O
Et
Pr
O
i Pr
not comprehensively examined. The MeHNL-catalyzed
HCN addition to 4-substituted cyclohexanones (2) is mecha-
nistically comparable with the hydrogenation of cyclohex-
anones to the corresponding alcohols using NADH-
depending alcohol dehydrogenases (4).
Me
t Bu
CN
NO
CH2=C(Me)
Ph
2
g
2f'
Only very few samples of 4-substituted cyclohexanone
cyanohydrins have been reported in the literature (5–9). In
all cases, mixtures of cis/trans isomers are obtained. For the
4-methyl compound the cis:trans ratio is 1:2, while for the
4-tert-butyl-substituted derivative the cis:trans ratio is 1:3.
Because these ratios are also found under base catalysis (8),
it can be assumed that these ratios correspond to the thermo-
dynamic equilibria.
In recent times, HCN is often replaced by trimethylsilyl
cyanide in the addition to carbonyl compounds, giving the
corresponding O-trimethylsilyl cyanohydrins (10). With 4-
substituted cyclohexanones only the cyanosilylation of tert-
butyl- and benzyloxycyclohexanone was performed, yielding
in both cases the trans isomer as major product. With vari-
ous catalysts the percentage of the trans product in the reac-
tion of 4-tert-butylcyclohexanone with trimethylsilyl cyanide
could be increased up to 90% (11), compared with 80%
trans isomer obtained with 4-benzyloxycyclohexanone using
ZnI2 as catalyst (12).
anones, the 4-alkyl-substituted compounds 1a–g (13a–c)
were investigated.
For the enzymatic reactions of the ketones 1, the
hydroxynitrile lyases (R)-PaHNL from almond and (S)-
MeHNL from cassava were used. The results of the HNL-
catalyzed addition of HCN to the 4-alkyl substituted
cyclohexanones 1 (Scheme 1) are summarized in Table 1.
All investigated cyclohexanones 1 were found to be good
substrates for both enzymes. The PaHNL-catalyzed conver-
sion selectively afforded the trans-cyanohydrins (trans-2),
while with catalyst MeHNL the corresponding cis isomers
(cis-2) were formed almost exclusively for the larger 4-
substituents. As can be seen from Table 1, the substituent R
clearly influences the reactivity of the (R)-PaHNL-catalyzed
reaction: with increasing steric demand of the R group the
conversion rate is markedly diminished. The stereo-
selectivity, however, is fairly high in all cases with one ex-
ception; the tert-butyl derivative 1e reacts very slowly,
therefore the chemical addition becomes more dominant,
causing diminished stereoselectivity (cis:trans = 10:90).
With the recombinant MeHNL from cassava, all substrates
1 were converted faster to the cyanohydrins compared with
PaHNL (whose selectivity is almost independent of the
steric demand of R) (Table 1). In contrast to PaHNL,
Results and discussion
Hydroxynitrile lyase-catalyzed HCN addition to 4-
alkylcyclohexanones 1 (2)
To investigate the scope of the cis/trans selectivity of the
enzyme-catalyzed HCN addition to 4-substituted cyclohex-
© 2002 NRC Canada

Effenberger et al.
Table 2. Experimental crystallographic data for compounds 2f >, 4b>, and 4h>.5
673
Compd
2f >
4b>
4h>
Formula
C17H18N2O4
0.65 × 0.25 × 0.01
314.33
C15H16N2O5
0.8 × 0.8 × 0.07
304.30
C16H16N2O6
1.1 × 0.1 × 0.07
332.31
Crystal size (mm)
FW (g mol–1)
Space group
Cell parameters
a (Å)
b (Å)
c (Å)
a (°)
b (°)
P1
P21/n
P21/c
6.8616(8)
7.1533(14)
17.564(3)
80.622(12)
80.239(11)
83.077(10)
834.4(2)
2
6.9275(12)
7.1416(13)
30.957(4)
90.00
90.952(12)
90.00
10.923(3)
6.436(2)
23.184(3)
90.00
91.721(14)
90.00
ꢀ (°)
V (Å3)
Z
1531.3(4)
4
1629.0(6)
4
ꢁcalcd. (g cm–3)
Data collectiona
Total reflections
Unique reflections
Refinement
R/Rw (F)
1.251
1.320
1.355
2390
2173
3276
3018
2544
2400
0.081/0.2178
236
1.040
–0.241
0.300
0.0586/0.1297
200
1.077
–0.235
0.308
0.0595/0.1239
218
1.193
–0.190
0.209
No. of variables
GoF
Dꢁmin (e Å–3)
Dꢁmax (e Å–3)
aT = 293 K, Nicolet P3 diffractometer, MoKa (ꢂ = 0.71073) or Siemens P4 diffractometer, Cu Ka (ꢂ = 1.54178) radiation.
Fig. 2. ORTEP view of (a) 4-methoxy-1-(4-nitrobenzoyloxy)cyc-
lohexanecarbonitrile (4b>); (b) 4-acetoxy-1-(4-nitrobenzoyloxy)cy-
clohexanecarbonitrile (4h>).
Fig. 1. ORTEP view of 4-isopropenyl-1-(4-nitrobenzoyloxy)cy-
clohexanecarbonitrile (2f >).
(a)
C8
C2
(b)
O1
C3
C2
C8
MeHNL is cis-selective and the stereoselectivity of the HCN
addition strongly depends on the size of R, as can be clearly
seen in the reactions of the homologues 1a–c (R = Me, Et,
Pr, respectively).
The structural assignment of the isomers by 13C NMR
spectroscopy followed from comparison with literature data
(13b). The C-1 atom signal in the cis isomer is clearly
shifted to a higher field compared with that of the trans iso-
mer (see Table 4). Furthermore, the X-ray structure (14) of
the nitrobenzoyl derivative 2f> (Fig. 1, Table 2), obtained by
nitrobenzoylation of the MeHNL-derived main isomer 2f
(Scheme 1), unequivocally confirms the assignment.
5 Supplementary material has been deposited with the Cambridge Crystallographic Data Centre. Copies of the data can be obtained, free of
charge, on quoting the depository number CCDC-174989 (2f >), CCDC-169991 (4b>), and CCDC-179064 (4h > ) from CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. (Fax: 44–1223–336033 or e-mail: deposit@ccdc.cam.ac.uk).
© 2002 NRC Canada

674
Can. J. Chem. Vol. 80, 2002
Table 3. Formation of 4-alkoxy- and 4-alkanoyloxycyclohexanone cyanohydrins 4 by (R)-PaHNL and (S)-MeHNL-catalyzed addition of
HCN to 4-substituted cyclohexanones 3.
(S)-MeHNL
(R)-PaHNL
Chemical addition
t
Conv.
(%)
cis:trans
(%)
t
Conv.
(%)
cis:trans
(%)
Conv.
(%)
cis:trans
(%)
Substrate
(h)
(h)
1
1
1
2.5
46
22
96
1
2
5
7
7
1
2
7
48
46
22
19
1
2
5
7
72
3a
3b
3c
3d
3e
3f
3g
3h
3i
80
quant
99
quant
52
99
45
92
92
76
43:57
28:72
61:39
87:13
90:10
87:13
82:18
66:34
69:31
60:40
58:42
88:12
90
97
82
60
18
97
99
97
85
99
98
89
39:61
9:91
11:89
14:86
16:84
8:92
2:98
5:95
9:91
9:91
52
21
34
17
2
2
9
8
17
4
45:55
45:55
43:57
46:54
47:53
45:55
45:55
57:43
60:40
63:37
61:39
71:29
3j
3k
3l
71
72
4:96
29:71
7
24
Scheme 3.
Scheme 2.
OH
O
HCl/EtOH
+
HCN
O
cis-2c
COOEt
Pr
R
3
5
(R)-PaHNL
or
(S)-MeHNL
Ac2O/pyridine
DMAP, CH2Cl2
iPr2O, rt
O
O
OH
CN
CN
O
O
CH3
OH
+
O
O
O
R
LiN(SiMe3)2
R
R
COOEt
Pr
Pr
cis-4
trans-4
−78°C
OH
7
6
O
CN
4-O2NC6H4
l
for
4b,h
pyridine/DMAP
O
The HNL-catalyzed HCN addition to the 4-alkyloxy- and
4-alkanoyloxycyclohexanones 3 is depicted in Scheme 2,
and the results are listed in Table 3.
NO2
4b',h'
Analogous to cyclohexanones 1, compounds 3 were also
converted using PaHNL as the catalyst with moderate to
high stereoselectivity to trans isomers 4. The trans selectiv-
ity of PaHNL with the substrates 3b–l is comparable with
the behavior of alkylcyclohexanones 1. In the case of 4-
hydroxycyclohexanone 3a, both enzymes (PaHNL and
MeHNL) show only a very low stereoselectivity. The
MeHNL-catalyzed addition of HCN to compounds 3 again
results in the preferred formation of the cis isomers (cis-4),
with one exception. In the conversion of 3b (R = MeO) the
trans isomer dominates. For benzyloxycyclohexanone 3g a
long reaction time is required and a slight decrease of the cis
stereoselectivity at low conversion was also observed.
The isomers were assigned by the chemical shift of the C-
4 atom in 13C NMR spectra and, due to deficiency of litera-
ture data, the structure was also determined by X-ray crys-
tallographic analysis (14). The isomers trans-4b and trans-
4h, obtained in the PaHNL-catalyzed HCN addition, were
crystallized as nitrobenzoyl derivatives 4b> and 4h>
(Scheme 2, Fig. 2, Table 2). As can be seen from Fig. 2,
both compounds exist as trans isomers, confirming the as-
signment.
3, 4 R=
3, 4
R=
3, 4
R=
O
O
a
b
c
H
h
k
Me
Et
Me
O
O
O
i
l
d
e
Pr
i Bu
CH2=CHCH2
PhCH2
f
j
g
Hydroxynitrile lyase-catalyzed HCN addition to 4-
alkyloxy- and 4-alkanoyloxycyclohexanones 3
In addition, to known cyclohexanones 3a–h and 3l (13d–i),
the 4-alkanoyloxycyclohexanones 3i–k had to be prepared.
For this purpose, 4-hydroxycyclohexanone (3a) was acylated
in the presence of pyridine and catalytic amounts of
dimethylaminopyridine (DMAP) with either the respective
acid chloride or anhydride to give the cyclohexanones 3i–k
in 45–65% yields (not optimized; see Experimental).
© 2002 NRC Canada

Effenberger et al.
675
Table 4. Spectroscopic data of the 4-substituted cyclohexanone cyanohydrins 2c, 2f, and 4a–l.
Compd
1H NMR (250 MHz) (J in Hz)
13C NMR (63 MHz)
0.89 (t, J = 6.9, 3H, CH3), 1.26–1.47 (m, 7H, 2 CH, 4-CH,
(CH2)2CH3), 1.53–1.64 (m, 2H, 2 CH), 1.83–1.87 (m, 2H,
2 CH), 2.16–2.21 (m, 2H, 2 CH), 2.91 (br s, 1H, OH)
trans-2c
14.24 (CH3), 20.10 (CH2CH2CH3), 29.60 (CH2),
35.79, 38.28 (C4, CH2CH2CH3), 38.03 (CH2),
70.68 (C1), 121.69 (CN)
cis-2c
0.89 (t, J = 7.0, 3H, CH3), 1.13–1.39 (m, 7H, 2 CH, 4-CH,
(CH2)2CH3), 1.60–1.67 (m, 2H, 2 CH), 1.78–1.90 (m, 2H,
2 CH), 2.03–2.10 (m, 2H, 2 CH), 2.39 (br s, 1H, OH)
14.23 (CH3), 19.90 (CH2CH2CH3), 26.40 (CH2),
35.14, 38.11 (C4, CH2CH2CH3), 36.16 (CH2),
67.29 (C1), 122.78 (CN)
trans-2f
cis-2f
1.48–1.72 (m, 4H, 4 CH), 1.74 (s, 3H, CH3), 1.86–1.99 (m, 3H,
3 CH), 2.23–2.29 (m, 2H, 2 CH), 3.16 (br s, 1H, OH), 4.74–
4.76 (m, 2H, =CH2)
20.82 (CH3), 28.28, 38.03 (CH2), 43.56 (C4),
70.32 (C1), 109.66 (=CH2), 121.54 (CN),
148.14 (C=)
1.64–1.67 (m, 4H, 4 CH), 1.72 (s, 3H, CH3), 1.82–2.01 (m, 3H,
3 CH), 2.13–2.20 (m, 2H, 2 CH), 2.79 (br s, 1H, OH), 4.71–
4.74 (m, 2H, =CH2)
20.84 (CH3), 24.98, 36.48 (CH2), 43.23 (C4),
66.56 (C1), 109.40 (=CH2), 122.83 (CN),
148.70 (C=)
trans-4aa
cis-4aa
1.53–2.13 (m, 6H, 6 CH), 2.21–2.35 (m, 2H, 2 CH), 2.86 (s,
1H, OH), 2.93 (s, 1H, OH), 3.79 (d, J = 2.0, 1H, 4-CH)
29.63, 33.36 (CH2), 66.34, 67.43 (C1, C4), 121.68
(CN)
1.47–2.39 (m, 8H, 4 CH2), 2.59 (br s, 2H, OH), 3.81–3.94 (m,
1H, 4-CH)
28.70, 31.56 (CH2), 62.64 (C1), 65.29 (C4),
121.18 (CN)
trans-4ba
cis-4b
1.64–2.22 (m, 8H, 4 CH2), 3.00 (br s, 1H, OH), 3.28–3.33 (m,
1H, 4-CH), 3.34 (s, 3H, CH3O)
26.20, 33.99 (CH2), 55.95 (CH3O), 68.37 (C1),
75.39 (C4), 121.80 (CN)
1.60–2.23 (m, 8H, 4 CH2), 3.08 (br s, 1H, OH), 3.28–3.41 (m,
1H, 4-CH), 3.32 (s, 3H, CH3O)
26.38, 33.32 (CH2), 55.80 (CH3O), 68.89 (C1),
73.75 (C4), 121.80 (CN)
trans-4ca
1.20 (t, J = 7.0, 3H, CH3CH2O), 1.63–1.76 (m, 4H, 4 CH),
1.89–2.06 (m, 2H, 2 CH), 2.19–2.23 (m, 2H, 2 CH), 3.36–
3.40 (m, 2H, OH, 4-CH), 3.50 (q, J = 7.0, 2H, CH3CH2O)
15.58 (CH3), 26.89, 34.28 (CH2), 63.56 (CH3CH2O),
68.51 (C1), 73.82 (C4), 121.89 (CN)
cis-4ca
trans-4da
cis-4da
trans-4e
cis-4e
1.21 (t, J = 7.0, 3H, CH3CH2O), 1.63–1.76 (m, 3H, 3 CH),
1.88–2.23 (m, 6H, OH, 5 CH), 3.36–3.43 (m, 1H, 4-CH),
3.46–3.52 (m, 2H, CH3CH2O)
15.56 (CH3), 26.78, 33.41 (CH2), 63.34
(CH3CH2O), 68.50 (C1), 72.02 (C4), 121.91
(CN)
0.92 (t, J = 7.6, 3H, CH3(CH2)2O), 1.54–2.23 (m, 10H,
CH3CH2CH2O, 4 CH2), 3.33–3.47 (m, 4H, CH3CH2CH2O,
4-CH, OH)
10.65 (CH3), 23.27 (CH3CH2CH2O), 26.74, 34.18
(CH2), 68.41 (C1), 70.10 (CH3CH2CH2O),
73.83 (C4), 121.97 (CN)
0.92–0.96 (m, 3H, CH3(CH2)2O), 1.53–2.23 (m, 10H,
CH3CH2CH2, 4 CH2), 3.20–3.50 (m, 4H, CH3CH2CH2, 4-CH,
OH)
10.68 (CH3), 23.24 (CH3CH2CH2O), 26.74, 34.18
(CH2), 68.41 (C1), 70.10 (CH3CH2CH2O),
73.83 (C4), 121.97 (CN)
0.90 (d, J = 6.6, 6H, CH3), 1.13–2.23 (m, 9H, 4 CH2,
CH(CH3)2), 3.00 (br s, 1H, OH), 3.17 (d, J = 6.0, 2H,
CH2CH), 3.33–3.36 (m, 1H, 4-CH)
19.42 (CH3), 25.60 (CH2), 28.76 (CH2CH), 34.04
(CH2), 69.06 (C1), 73.84 (C4), 75.28 (CH2CH),
121.99 (CN)
0.90 (d, J = 6.6, 6H, CH3), 1.13–2.23 (m, 9H, 4 CH2,
CH(CH3)2), 3.00 (br s, 1H, OH), 3.15 (d, J = 6.5, 2H,
CH2CH), 3.44 (m, 1H, 4-CH)
19.42 (CH3), 26.88 (CH2), 28.76 (CH2CH), 33.32
(CH2), 67.96 (C1), 71.85 (C4), 75.03 (CH2CH),
121.90 (CN)
trans-4f
cis-4f
1.64–2.24 (m, 8H, 4 CH2), 2.99 (br s, 1H, OH), 3.43–3.49 (m,
1H, 4-CH), 3.97–4.00 (m, 2H, CH2CH=), 5.17–5.34 (m, 2H,
=CH2), 5.88–5.95 (m, 1H, CH2CH=)
26.62, 34.06 (CH2), 68.33 (C1), 69.19 (CH2CH=),
73.31 (C4), 117.78 (=CH2), 121.79 (CN),
134.98 (CH2CH=)
1.71–2.15 (m, 8H, 4 CH2), 2.94 (br s, 1H, OH), 3.48–3.58 (m,
1H, 4-CH), 3.96–4.01 (m, 2H, CH2CH=), 5.14–5.32 (m, 2H,
=CH2), 5.83–5.98 (m, 1H, CH2CH=)
26.78, 33.37 (CH2), 68.83 (C1), 69.00 (CH2CH=),
71.56 (C4), 116.70 (=CH2), 121.79 (CN),
134.98 (CH2CH=)
trans-4g
1.67–1.81 (m, 4H, 4 CH), 1.95–2.03 (m, 2H, 2 CH), 2.93 (br s,
1H, OH), 3.45–3.54 (m, 1H, 4-CH), 4.51–4.56 (m, 2H,
CH2Ph), 7.25–7.38 (m, 5H, Ph)
26.54, 33.99 (CH2), 68.34 (C1), 70.17 (CH2Ph),
73.27 (C4), 121.78 (CN), 127.46, 127.63,
128.45, 138.48 (Ph)
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Can. J. Chem. Vol. 80, 2002
Table 4 (concluded).
Compd
1H NMR (250 MHz) (J in Hz)
13C NMR (63 MHz)
cis-4g
1.67–2.33 (m, 8H, 4 CH2), 3.50 (br s, 1H, OH), 3.57–3.60 (m,
1H, 4-CH), 4.50–4.52 (m, 2H, CH2Ph), 7.25–7.37 (m, 5H,
Ph)
26.81, 33.35 (CH2), 68.79 (C1), 70.13 (CH2Ph),
71.64 (C4), 121.84 (CN), 127.39, 127.56,
128.40, 138.47 (Ph)
trans-4h
1.68–1.85 (m, 4H, 4 CH), 1.87–2.10 (m, 5H, 2 CH, CH3), 2.13–
2.25 (m, 2H, 2 CH), 3.13 (br s, 1H, OH), 4.81–4.88 (m, 1H,
4-CH)
21.29 (CH3), 26.32, 34.05 (CH2), 67.96 (C1),
69.33 (C4), 121.61 (CN), 170.78 (C=O)
cis-4h
1.68–2.24 (m, 11H, 4 CH2, CH3), 3.79 (br s, 1H, OH), 4.91–
5.00 (m, 1H, 4-CH)
21.32 (CH3), 26.53, 33.47 (CH2), 68.02 (C1),
68.30 (C4), 121.57 (CN), 170.80 (C=O)
trans-4ia
1.15 (t, J = 7.6, 3H, CH3CH2), 1.64–1.78 (m, 2H, 2 CH), 1.82–
1.87 (m, 2H, 2 CH), 1.93–2.04 (m, 2H, 2 CH), 2.17–2.22 (m,
2H, 2 CH), 2.34 (q, J = 7.6, 2H, CH3CH2), 3.46 (br s, 1H,
OH), 4.85 (tt, J = 7.7, 3.6, 1H, 4-CH)
9.15 (CH3), 26.29 (CH2), 27.88 (CH3CH2), 33.97
(CH2), 67.89 (C1), 69.14 (C4), 121.73 (CN),
174.27 (C=O)
cis-4ia
1.15 (t, J = 7.6, 3H, CH3CH2), 1.81–1.88 (m, 2H, 2 CH), 1.92–
2.04 (m, 5H, 5 CH), 2.17–2.22 (m, 1H, CH), 2.32–2.37 (m,
2H, CH3CH2), 3.52 (br s, 1H, OH), 4.85 (tt, J = 5.6, 3.3, 1H,
4-CH)
9.15 (CH3), 26.61 (CH2), 27.89 (CH3CH2), 33.48
(CH2), 67.88 (C1), 68.17 (C4), 121.49 (CN),
174.03 (C=O)
trans-4j
1.17 (d, J = 7.0, 6H, (CH3)2CH), 1.67–1.96 (m, 4H, 4 CH),
1.97–2.05 (m, 2H, 2 CH), 2.14–2.24 (m, 2H, 2 CH), 2.56 (q,
J = 7.0, 1H, (CH3)2CH), 3.69 (br s, 1H, OH), 4.84 (tt, J =
7.4, 3.6, 1H, 4-CH)
18.96 (CH3), 26.17, 33.86 (CH2), 34.21 (CH),
67.81 (C1), 68.96 (C4), 121.81 (CN), 176.99
(C=O)
cis-4j
1.17 (d, J = 7.0, 6H, (CH3)2CH), 1.64–2.24 (m, 8H, 4 CH2),
2.50–2.63 (m, 1H, (CH3)2CH), 3.84 (br s, 1H, OH), 4.91–5.04
(m, 1H, 4-CH)
18.96 (CH3), 26.64, 33.48 (CH2), 34.21 (CH),
67.59 (C1), 68.16 (C4), 121.81 (CN), 176.49
(C=O)
trans-4k
0.96 (t, J = 7.4, 3H, CH3), 1.58–1.89 (m, 6H, 4 CH,
CH3CH2CH2), 1.96–2.06 (m, 2H, 2 CH), 2.10–2.24 (m, 2H,
2 CH), 2.30 (t, J = 7.4, 2H, CH3CH2CH2), 3.80 (br s, 1H,
OH), 4.94 (tt, J = 7.5, 3.6, 1H, 4-CH)
13.61 (CH3), 18.53 (CH3CH2), 26.32, 33.95
(CH2), 36.49 (CH3CH2CH2), 67.86 (C1),
69.15 (C4), 121.78 (CN), 173.58 (C=O)
cis-4k
0.94–0.99 (m, 3H, CH3), 1.63–1.71 (m, 2H, CH3CH2CH2), 1.81–
2.12 (m, 8H, 4 CH2), 2.27–2.39 (m, 2H, CH3CH2CH2), 3.82
(br s, 1H, OH), 4.94 (tt, J = 5.7, 3.4, 1H, 4-CH)
13.62 (CH3), 18.53 (CH3CH2), 26.66, 33.53
(CH2), 36.47 (CH3CH2CH2), 67.76 (C1),
68.29 (C4), 121.57 (CN), 173.02 (C=O)
trans-4la
cis-4la
1.20 (s, 9H, (CH3)3C), 1.71–1.78 (m, 1H, CH), 1.81–1.89 (m,
2H, 2 CH), 1.93–2.09 (m, 4H, 4 CH), 2.13–2.20 (m, 1H,
CH), 3.32 (br s, 1H, OH), 4.81–4.85 (m, 1H, 4-CH)
26.68 (CH2), 27.14 (CH3), 33.45 (CH2), 38.89
(C(CH3)3), 67.76 (C1), 68.75 (C4), 121.81
(CN), 178.18 (C=O)
1.21 (s, 9H, (CH3)3C), 1.71–2.16 (m, 8H, 4 CH2), 3.60 (br s,
1H, OH), 4.93 (s, 1H, 4-CH)
26.69 (CH2), 27.18 (CH3), 33.42 (CH2), 38.91
(C(CH3)3), 67.31 (C1), 68.00 (C4), 121.41
(CN), 177.75 (C=O)
a500 MHz spectra.
synthetic route to cis-spirotetronic acid 7 from cyanohydrin
cis-2c is shown in Scheme 3.
Preparation of spirotetronic acids
As mentioned in the introduction, isomerically pure cyclo-
hexanone cyanohydrins are important as starting compounds
in the stereoselective synthesis of tetronic acids known as
potent insecticides or herbicides (1). In a recent publication
(15), we described the preparation of optically active 5,5-
disubstituted tetronic acids starting from chiral ketone cya-
nohydrins. This reaction sequence, involving a Pinner reac-
tion of the cyanohydrin to give the corresponding hydroxy
ester, acylation of the hydroxyl group, and subsequent
hexamethyldisilazanide (LiN(SiMe3)2) mediated ring closure
at –78°C following a known procedure (16), could be ap-
plied also for the preparation of spirotetronic acids. The
In the (S)-MeHNL-catalyzed HCN addition to 4-
propylcyclohexanone 1c, cyanohydrin 2c was isolated in an
isomeric ratio cis:trans = 96:4 (Table 1). Compound 2c was
directly converted to hydroxy ester 5 by treatment with HCl
in ethanol at 90–100°C with 84% yield (15). Acetylation of
hydroxy ester 5 with acetic anhydride–pyridine and DMAP
in dichloromethane gave acetoxy carboxylate 6 in 83%
yield. The cyclization of 6, resulting in the spirotetronic acid
7 with 73% yield, was performed by using LiN(SiMe3)2 in
THF at –78°C. Recrystallization of 7 from chloroform gave
a single crystal suitable for X-ray crystallographic analysis
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677
Table 5. Elemental analysis of silylated cyanohydrins 4a–l.
Mol. formula
(Mol. weight)
Calcd./found
C
Mol. formula
(Mol. weight)
Calcd./found
C
Compd
H
N
Compd
H
N
4a
C13H27NO2Si2
(285.5)
54.68
54.53
9.53
9.47
4.91
5.08
4g
C17H25NO2Si
(303.5)
67.28
67.19
8.30
8.21
4.62
4.58
4b
4c
C11H21NO2Si
(227.4)
58.11
58.18
9.31
9.31
6.16
6.10
4h
4i
C12H21NO3Si
(255.4)
56.44
56.60
8.29
8.23
5.48
5.43
C12H23NO2Si
(241.4)
59.71
59.53
9.60
9.65
5.80
5.79
C13H23NO3Si
(269.4)
57.96
58.04
8.60
8.60
5.20
5.05
4d
4e
4f
C13H25NO2Si
(255.4)
61.13
61.01
9.86
9.89
5.48
5.41
4j
4k
4l
C14H25NO3Si
(283.4)
59.33
59.47
8.89
8.86
4.94
4.89
C14H27NO2Si
(269.5)
62.40
62.48
10.10
10.01
5.20
5.34
C14H25NO3Si
(283.4)
59.33
59.31
8.89
8.85
4.94
4.70
C13H23NO2Si
(253.4)
61.61
61.53
9.15
9.27
5.53
5.46
C15H27NO3Si
(297.5)
60.56
60.62
9.15
9.17
4.71
4.62
(17). The crystal structure unambiguously shows the cis con-
formation of the spirotetronic acid 7 (17).
Stereoselectivity of cyanohydrin formation from 4-
alkoxy- and 4-alkanoyloxycyclohexanones 3
The improved cis stereoselectivity with increasing size of
the R substituent is also observed for the MeHNL-catalyzed
reactions of 4-alkyloxy-substituted homologues 3c–f. Alkan-
oyloxy-substituted derivatives 3h–k, however, gave only low
cis selectivity in this addition reaction. A plausible interpre-
tation of this result so far is not possible. Polar interactions
and hydrogen bonding of the alkanoyloxy substituents with
amino acids in the surrounding of the active site of the en-
zyme are assumed to be responsible for the different behav-
ior in comparison with 4-alkylcyclohexanones 1.
Since the reactions of the 4-isobutyloxy and the 4-
benzyloxy derivatives (3e and 3g) occur with relatively high
cis selectivity, stereoisomerically pure cis-4-hydroxycyclo-
hexanone cyanohydrin 4a can be prepared either by hydroly-
sis or by hydrogenolytic cleavage of 3e and 3g, respectively.
As can be seen from Tables 1 and 3 and in contrast to
MeHNL, the PaHNL-catalyzed addition of HCN to 4-
substituted cyclohexanones 1 as well as 3 gives, in most
cases, high trans selectivity independent of the kind of
substituent. An explanation for PaHNL’s high trans selectiv-
ity is not possible, since too little is known about its X-ray
structure (18); a substrate–enzyme complex would be very
helpful for the interpretation of our experimental results.
Mechanistic interpretation of the cis/trans selectivity of
MeHNL-catalyzed reactions
The stereoselectivity of the (S)-MeHNL-catalyzed reac-
tion of 4-alkylcyclohexanones 1 can be explained as follows
(2). From the X-ray crystal structure of (S)-MeHNL it is
known that the active site is accessible via a narrow channel
and consists of a small (S1) and a larger (S2) binding pocket
(3a). In the active site the carbonyl group of the incoming
substrate is fixed by hydrogen bonds from Thr11 and Ser80,
as shown in the acetone-complexed MeHNL crystal structure
(3a). The superposition of the catalytically inactive mutant
MeHNL-Ser80Ala complexed with acetone cyanohydrin
onto the MeHNL–acetone structure clearly reveals that the
cyanohydrin is fixed in an analogous manner (3b). Cyclo-
hexanones 1 are assumed to bind to the enzyme’s active site
in the channel either in an upright or a flat mode (2). In both
cases, the cyanide ion attacks the substrate from the same di-
rection, namely from below, giving either the cis isomer
from the upright position or the trans isomer from the flat
position. Taking into account the hydrogen bonding of the
substrate and the chair-form of the cyclohexane ring with
preferred equatorial 4-substituent R, in the case of
cyclohexanones with a small R substituent, especially 1a
with R = Me, both positions in the channel are possible
without unfavourable steric interactions between the sub-
strate and the channel wall. Hence, the formation of both cis
and trans isomers is possible. In this case, the percentage of
the isomers varies and depends on enzyme activity and gen-
eral reaction conditions. With increasing size of R, however,
the upright binding mode is favored. As demonstrated by
molecular modeling calculations of 4-tert-butylcyclo-
hexanone cyanohydrin (2e), the flat position would lead to
severe steric interactions between the substrate and the chan-
nel wall, whereas vertically arranged 2e fits perfectly in the
channel without unfavourable interactions (2). Hence, the
formation of the cis isomer dominates.
Experimental
General procedure for the preparation of
cyclohexanones 3i–k
To a solution of 3a (11.5 mmol) in CH2Cl2 (20 mL) or
neat 3a (13.1–15.4 mmol) was added pyridine (20–25 mL),
DMAP (30–50 mg), and the respective acid chloride
propionyl chloride and isobutyryl chloride (2 equiv) or bu-
tyric anhydride (2 equiv), and the reaction mixture was stirred
for 3 h (3i, 3j) or 5 h (3k) at room temperature. Then water
(120 mL) was added, and the aqueous layer was extracted
with diethyl ether (3 × 70 mL). The combined extracts were
© 2002 NRC Canada

678
Can. J. Chem. Vol. 80, 2002
washed with diluted HCl until neutral, dried (Na2SO4), and
concentrated. The crude products were distilled.
Determination of conversion and isomeric ratio
To a solution of crude 2 or 4 (10 L) in CH2Cl2 (500 L)
was added acetic anhydride (50 L) and DMAP (15 mg),
and the reaction mixture was allowed to stand at room tem-
perature for 15 min. The mixture was then filtered through a
silica gel column (3 × 0.5 cm) with CH2Cl2 (4 mL). Conver-
sion and isomeric ratio were directly determined from the
filtrate by gas chromatography.
4-Propionyloxycyclohexanone (3i)
Yield: 45%; bp 80–82°C (0.1 Torr). H NMR (250 MHz,
1
CDCL3) d: 1.18 (t, J = 7.6 Hz, 3H, CH3CH2), 2.00–2.17 (m,
4H, 4 CH), 2.30–2.43 (m, 4H, 4 CH), 2.49–2.62 (m, 2H,
CH3CH2), 5.19 (quin, J = 4.8 Hz, 1H, 4-CH). 13C NMR
(63 MHz, CDCL3) d: 9.17 (CH3), 27.84 (CH3CH2), 30.44,
37.27 (CH2), 68.33 (C4), 173.81 (CO2), 209.95 (CO).
General procedure for the preparation of the
nitrobenzoylated derivatives 2f>, 4b>, and 4h>
4-Isobutyryloxycyclohexanone (3j)
Yield: 64%; bp 84–86°C (0.1 Torr). H NMR (250 MHz,
To a solution of 2f, 4b, or 4h (0.35 mmol or 3.2–
3.8 mmol, isomeric ratio given in Tables 1 and 3) in pyridine
(5–30 mL) was added DMAP (ca. 0.1 equiv) and p-
nitrobenzoyl chloride (1.5–2.0 equiv), and the reaction mix-
ture was stirred for the given time. Then water (10 or
100 mL) was added, the layers were separated, and the aque-
ous layer was extracted with diethyl ether (3 × 50 mL). The
combined extracts were washed with diluted HCl until neu-
tral, dried (Na2SO4), and concentrated. The residue was
chromatographed on silica gel with petroleum ether–ethyl
acetate (3:1 to 10:1).
1
CDCL3) d: 1.20 (d, J = 7.0 Hz, 6H, 2 CH3), 1.98–2.18 (m,
4H, 4 CH), 2.31–2.42 (m, 2H, 2 CH), 2.50–2.68 (m, 3H,
(CH3)2CH, CH2), 5.17 (tt, J = 5.6, 3.9 Hz, 1H, 4-CH). 13C
NMR (63 MHz, CDCL3) d: 19.01 (CH3), 30.42 (CH2), 34.21
(CH(CH3)2), 37.23 (CH2), 68.10 (C4), 176.42 (CO2), 209.94
(CO).
4-Butyryloxycyclohexanone (3k)
Yield: 65%; bp 91–93°C (0.1 Torr). H NMR (250 MHz,
1
CDCL3) d: 0.97 (t, J = 7.4 Hz, 3H, CH3), 1.60–1.76 (m, 2H,
CH2CH2CH3), 1.96–2.17 (m, 4H, 4 CH), 2.31–2.42 (m, 4H,
4 CH), 2.49–2.61 (m, 2H, CH2CH2CH3), 5.19 (quin, J =
4.8 Hz, 1H, 4-CH). 13C NMR (63 MHz, CDCL3) d: 13.66
(CH3), 18.56 (CH2CH2CH3), 30.49 (CH2), 36.46 (CH2CH2CH3),
37.29 (CH2), 173.02 (CO2), 209.92 (CO).
cis-4-Isopropenyl-1-(4-nitrobenzoyloxy)cyclohexanecarbo-
nitrile (2f >)
Reaction time: 7 d at room temperature; mp 107°C
1
(EtOH–CH2Cl2). H NMR (500 MHz, CDCL3) d: 1.52–1.60
(m, 2H, 2 CH), 1.73 (s, 3H, CH3), 1.84–1.87 (m, 2H, 2 CH),
2.02–2.08 (m, 3H, 3 CH), 2.75 (d, J = 13.2 Hz, 2H, 2 CH),
4.72 and 4.78 (each s, 1H, =CH2), 8.21–8.35 (m, 4H, Ph).
13C NMR (126 MHz, CDCL3) d: 20.98 (CH3), 25.50, 34.26
(CH2), 42.62 (C4), 71.51 (C1), 109.75 (=CH2), 118.76 (CN),
123.86, 130.90, 134.44, 150.97 (Ph), 147.91 (C=), 162.38
(C=O).
General procedure for the (R)-PaHNL-catalyzed
preparation of cyclohexanone cyanohydrins 2 and 4
A solution of (R)-PaHNL (19) (100 U per 100 mg sup-
port, total 200 U, 78 L) was added to cellulose (Elcema-
Cellulose P100PSC (Degussa); 1 g soaked in 10 mL of
0.02 M sodium citrate buffer, pH 3.3, for 2 h, and filtered
off) followed by addition of diisopropyl ether (5 mL), sub-
strate 1 or 3 (1 mmol), and HCN (20) (150 L, 3.9 mmol).
After stirring at room temperature for the times given in Ta-
bles 1 and 3, the support was filtered off, washed twice with
diethyl ether, and the combined filtrates were concentrated
under vacuum. For physical data see Tables 4 and 5.
trans-4-Methoxy-1-(4-nitrobenzoyloxy)cyclohexanecarbo-
nitrile (4b>)
1
Reaction time: 3 h at 50°C; mp 146°C (MeOH). H NMR
(250 MHz, CDCL3) d: 1.81–2.57 (m, 8 H, 4 CH2), 3.35–3.45
(m, 1H, 4-CH), 3.37 (s, 3H, CH3O), 8.18–8.35 (m, 4H, Ph).
13C NMR (63 MHz, CDCL3) d: 25.77, 30.81 (CH2), 56.03
(CH3O), 72.91 (C1), 74.19 (C4), 117.95 (CN), 123.78,
130.95, 134.40, 150.98 (Ph), 162.48 (C=O). Anal. calcd. for
C15H16N2O5: C 59.21, H 5.30, N 9.21; found: C 59.29, H 5.37,
N 8.97.
General procedure for the (S)-MeHNL-catalyzed
preparation of cyclohexanone cyanohydrins 2 and 4
A solution of (S)-MeHNL (21) (100 U per 100 mg sup-
port, total 180–200 U, 92–93 L) was added to nitro-
cellulose [Blotting-Membrane (Schleicher & Schuell); 1 g,
soaked in 50 mL of 0.02 M sodium citrate buffer, pH 3.3,
for 0.5 h; the buffer was decanted and nitrocellulose centri-
fuged (5700 × g for 30 min) and dried under high vacuum
for 5 h], followed after 15 min by addition of diisopropyl
ether (5 mL), substrate 1 or 3 (1 mmol), and HCN (150 L,
3.9 mmol). The reaction was performed as described above.
For physical data see Tables 4 and 5.
trans-4-Acetoxy-1-(4-nitrobenzoyloxy)cyclohexanecarbo-
nitrile (4h>)
Reaction time: 7 d at room temperature; mp 173°C
1
(EtOH). H NMR (250 MHz, CDCL3) d: 1.84–2.10 (m, 4H,
4 CH), 2.10 (s, 3H, CH3), 2.17–2.28 (m, 2H, 2 CH), 2.51–
2.62 (m, 2H, 2 CH), 4.92 (tt, J = 7.4, 3.9 Hz, 1H, 4-CH),
8.18–8.36 (m, 4H, Ph). 13C NMR (63 MHz, CDCL3) d:
21.22 (CH3), 26.26, 31.45 (CH2), 68.41 (C4), 72.55 (C1),
117.61 (CN), 123.82, 131.00, 134.15, 151.06 (Ph), 162.48
(PhC=O), 170.38 (CH3C=O). Anal. calcd. for C16H16N2O6:
C 57.83, H 4.85, N 8.43; found: C 57.66, H 4.89, N 8.34.
Chemical reaction (blank experiment)
The chemical HCN addition was performed analogously
with the enzymatic reaction, however, the enzyme solution
was replaced by the same volume of 0.02 M sodium acetate
buffer, pH 5.4. The reaction times correspond with those of
the (R)-PaHNL-catalyzed reaction.
Ethyl cis-1-hydroxy-4-propylcyclohexanecarboxylate (5)
A solution of cis-2c (5.0 g, 29.9 mmol) in ethanolic HCl
solution (60 mL) was stirred at 90–100°C for 16 h in a pres-
sure vessel. To open the vessel, it was cooled with ice water.
© 2002 NRC Canada

Effenberger et al.
679
The reaction mixture was diluted with diethyl ether (40 mL)
and ice water was added until the white precipitate dis-
solved. The layers were separated and the aqueous layer was
extracted three times with diethyl ether. The combined or-
ganic layers were washed with sat. NaHCO3 solution, dried
(Na2SO4), and concentrated. The residue was distilled under
vacuum to give 5.4 g (84%) of 5; bp 84°C (0.01 mm Hg).
1H NMR (500 MHz, CDCL3) d: 0.88 (t, J = 7.3 Hz, 3H,
CH3CH2), 1.19–1.38 (m, 10H), 1.60–1.81 (m, 6H), 2.92 (s,
1H, OH), 4.22 (q, J = 7.0 Hz, 2H, CH3CH2). 13C NMR
(126 MHz, CDCL3) d: 14.19, 14.34, 19.89, 27.54, 36.63,
39.34 (CH3, CH2), 61.66 (CH3CH2O), 73.99 (C-OH), 177.76
(C=O). Anal. calcd. for C12H22O3: C 67.26, H 10.35; found:
C 67.04, H 10.43.
Frey for X-ray crystallographic analysis, and Dr. Angelika
Baro for preparing the manuscript.
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1
give 5.4 g (83%) of 6; bp 105°C (0.01 mm Hg). H NMR
(500 MHz, CDCL3) d: 0.88 (t, J = 7.2 Hz, 3H, CH3CH2),
1.12–1.35 (m, 10H), 1.63–1.76 (m, 4H), 2.09 (s, 3H,
CH3CO), 2.23 (dd, J = 14.9, 2.3 Hz, 2H, 2,6-CHeq), 4.17 (q,
J = 7.0 Hz, 2H, CH3CH2). 13C NMR (126 MHz, CDCL3) d:
14.06, 14.31, 19.89, 21.14, 27.63, 31.85, 36.17, 39.16 (CH3,
CH2), 61.08 (CH3CH2), 79.87 (C-O), 169.90, 172.89 (C=O).
Anal. calcd. for C14H24O4: C 65.60, H 9.44; found: C 65.58,
H 9.43.
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Pharm. Bull. 45, 43 (1997).
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(2000).
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18. I. Dreveny, K. Gruber, A. Glieder, A. Thompson, and C.
Kratky. Structure (Cambridge), 9, 803 (2001).
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343 (1994).
cis-4-Hydroxy-8-propyl-1-oxaspiro[4.5]dec-3-en-2-one (7)
To a solution of LiN(SiMe3)2 [prepared from hexamethyl-
disilazane (3.3 mL, 16 mmol) and a 1.6 M solution of n-BuLi
in hexane (10 mL, 16 mmol)] in THF (60 mL) at –78°C was
added a solution of 6 (2.0 g, 7.8 mmol) in THF (20 mL)
over 15 min. After stirring for 2 h (TLC control), water
(20 mL) was added and the reaction mixture was allowed to
warm to room temperature. The organic layer was extracted
twice with sat. NaHCO3 solution. The combined aqueous
layers were adjusted to pH 1 with conc. HCl and extracted
three times with ethyl acetate. The combined extracts were
dried (Na2SO4) and concentrated. The residue was
recrystallized from chloroform to give 1.2 g (73%) of 7 as
1
colorless crystals; mp 218°C. H NMR (250 MHz, DMSO-
d6) d: 0.87 (t, J = 6.8 Hz, 3H, CH3), 1.09–1.83 (m, 13H),
4.79 (s, 1H, =CH), 12.65 (br s, 1H, OH). 13C NMR
(126 MHz, DMSO-d6) d: 14.13, 19.28, 28.01, 32.35, 34.90
(CH3, CH2, CH), 82.57 (C-O), 86.33 (=CH), 172.04, 185.15
(C=O, C-OH). Anal. calcd. for C12H18O3: C 68.55, H 8.63;
found: C 68.46, H 8.70.
20. P. Kurtz. In Houben-Weyl, Methoden der Organischen
Chemie. Vol. 8. 4th ed. Thieme, Stuttgart. 1952. p. 255.
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35, 437 (1996).
Acknowledgments
This work was supported by the Fonds der Chemischen
Industrie and the Degussa AG. The authors thank the Bayer
AG for donation of 4-alkylcyclohexanones, Dr. Wolfgang
© 2002 NRC Canada