Studies on Rhizopus arrhizus mediated enantioselective reduction of arylalkanones

Article abstract of DOI:10.1016/S0040-4020(01)00134-X

The effect of substitution on the biotransformation of various arylalkanones using Rhizopus arrhizus was investigated. The organism was found to be promising for the reduction of phenylalkanones and arylethanones with good to excellent enantioselectivity. The reduction followed Prelog's rule giving the (S)-carbinols in all the cases. The enantioselectivity of the reaction improved with increasing size of the groups flanking the carbonyl function and the electron withdrawing capacity of the substituents in the aromatic ring. However, the yield was dramatically affected with increased hydrophobicity of the substrates.

Full text of DOI:10.1016/S0040-4020(01)00134-X

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 2833±2839
Studies on Rhizopus arrhizus mediated enantioselective reduction
of arylalkanones
Neeta A. Salvi and Subrata Chattopadhyayp
Bio-Organic Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
Received 7 September 2000; revised 8 January 2001; accepted 25 January 2001
AbstractÐThe effect of substitution on the biotransformation of various arylalkanones using Rhizopus arrhizus was investigated. The
organism was found to be promising for the reduction of phenylalkanones and arylethanones with good to excellent enantioselectivity. The
reduction followed Prelog's rule giving the (S)-carbinols in all the cases. The enantioselectivity of the reaction improved with increasing size
of the groups ¯anking the carbonyl function and the electron withdrawing capacity of the substituents in the aromatic ring. However, the
yield was dramatically affected with increased hydrophobicity of the substrates. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
During our recent studies on the biotransformation using
Rhizopus arrhizus, we have established its versatility for
stereoselective reduction of ketones.5,6 In addition, its
biomass was found to be effective for the removal of trace
amounts of radioactive pollutants from nuclear waste.7,8 It
was therefore interesting to evaluate the potentials of R.
arrhizus to bring about microbial reduction of aryl-
alkanones, as chiral arylalkylcarbinols are useful inter-
mediates for agrochemicals and pharmaceuticals.9,10
Hence, we studied the microbial reduction of a wide range
of substrates so as to understand the steric and electronic
effects of substituents on the reactivity and the stereo-
selectivity of the organism. The chosen substrates can be
sub-divided into three categories, viz. phenyl alkanones,
substituted phenyl ethanones and fused arylethanones.
The asymmetric reduction of ketones represents a pivotal
transformation1 in organic synthesis as the product carbinols
are often useful target bioactive compounds or their pre-
cursors. For this reaction, the use of an enzymatic protocol
offers an alternative to chemical methods and has aroused
interest among organic chemists.2a±c At present, various
redox enzymes are commercially available; however, their
widespread use is restricted due to the prohibitive cost and
the need to use costly cofactors in stoichiometric amounts.
In this regard, the use of whole cell systems is emerging as
an economical and eco-friendly alternative.2a±c Amongst
various microorganisms, the use of baker's yeast in asym-
metric reduction is very well documented.3a,b Although
operationally simple, the microbial methods often suffer
either from limited substrate speci®city of most of the
microbes and/ or moderate to good enantioselectivity except
in few cases. Thus, there is a need to develop more ef®cient
protocols for bioreduction. To this end, techniques have
recently been introduced to improve the enantioselectivity
of microbial reduction. These include use of the acetone
powder of Geotrichum candidum for reduction of para-
substituted acetophenones,4a application of puri®ed
enzymes from baker's yeast4b for reduction of alkanones
and use of various yeast strains4c in the presence of selective
enzyme inhibitors for reduction of a-keto esters, etc.
However, these protocols involve external addition of the
cofactor or tedious isolation of the enzymes. Exploration of
other microorganisms is an alternative approach to address
this issue.
2. Results and discussion
A series of aromatic ketones were subjected to bio-
reduction using R. arrhizus in modi®ed Czepak Dox
medium.11 In each case, the reaction was carried out
for different incubation periods so as to optimize the
Á
yield vis-a-vis enantiomeric purity. The product alcohols
were isolated and puri®ed by preparative TLC. The
optimized enantiomeric purities and yields for each of the
three classes of substrates are listed in Tables 1±3. In
general, the microbe showed moderate to excellent enantio-
preference in the reduction. A total of 36 substrates were
targeted for reduction. The organism could reduce 24 of
these compounds to furnish the (S)-carbinols in all the
cases. The degree of enantioselectivity was found to be
governed by the steric demands of the substrates and the
electronic effects of the substituents as revealed in the
following analysis.
Keywords: microbial reactions; reduction; ketones; enantioselective.
Corresponding author. Fax: 191-22-5505151;
e-mail: schatt@apsara.barc.ernet.in
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(01)00134-X

2834
N. A. Salvi, S. Chattopadhyay / Tetrahedron 57 (2001) 2833±2839
Table 1. Microbial reduction of 1-phenylalkanones using R. arrhizus
Entry No.
Substrate
Incub. period (days)
Product
Yield (%)a
Ee (%)b
Con®g.
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
7
7
7
4a
4b
4c
4d
4e
4f
±
±
±
±
33
53
42
45
15
15
0
0
0
0
69
80
92
92
92
92
±
±
±
±
S
S
S
S
S
S
±
±
±
±
S
S
S
7
14
14
14
14
14
14
4
9
10
11
12
13
1j
1k
1l
4k
4l
4m
26
15
60
34
74
82
7
2
1m
a
Isolated yields.
Based on H NMR analysis of the corresponding (R)-MTPA esters.
b
1
Table 2. Microbial reduction of 1-arylethanones using R. arrhizus
Entry No.
Substrate
Incub. period (days)
Product
Yield (%)a
Ee (%)b
Con®g.
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
51
72
62
59
58
63
10
55
72
59
42
15
14
15
15
68
68
91
94
96
10
12
67
46
72
85
93
92
93
94
99
90
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
9
10
11
12
13
14
15
16
a
Isolated yields.
Based on H NMR analysis of the corresponding (R)-MTPA esters.
b
1
Table 3. Microbial reduction of 1-polyarylethanones using R. arrhizus
Entry No.
Substrate
Incub. period (days)
Product
Yield (%)a
Ee (%)b
Con®g.
1
2
3
4
5
6
7
3a
3b
3c
3d
3e
3f
14
14
14
14
14
14
14
6a
6b
6c
6d
6e
6f
18
20
3
0
0
74
89
68
±
±
±
S
S
S
±
±
±
±
0
0
3g
6g
±
a
Isolated yields.
Based on H NMR analysis of the corresponding (R)-MTPA esters.
b
1
2.1. Reduction of 1-phenylalkanones
rate of the reaction, it was found that compounds 1a±d were
easily reduced within 7 days of incubation. Thereafter the
reaction was very slow and even after 14 days only 1e and 1f
could be reduced in poor yields, while longer alkanones,
1g±1j, could not be reduced. This might be attributed to
the size of the alkyl side chain and/or their lower solubility
in the reaction medium.
In order to explore the effect of size of the alkyl group on the
reactivity and the enantioselectivity, various 1-phenyl-
alkanones 1a±m were subjected to reduction with R.
arrhizus (Scheme 1). The result of the study is shown in
Table 1. Within this class, increasing length of the alkyl
chain (Table 1, entries 1±6) led to an increase in enantio-
selectivity giving the product alcohols in 69±92% enantio-
meric excess (ee). However, the effect tapered off beyond
the propyl group and no change in the ees was seen on
changing R from propyl to hexyl groups. In terms of the
Reduction of a-phenylacetophenone (deoxybenzoin, 1k)
proceeded with poor enantioselectivity as expected due to
the similar sizes of the groups ¯anking the carbonyl group.
Surprisingly 2-benzoylpyridine (1m) was converted into the

N. A. Salvi, S. Chattopadhyay / Tetrahedron 57 (2001) 2833±2839
2835
Scheme 1.
corresponding alcohol with appreciable yield (60%) and
enantioselectivity (82% ee) in spite of its apparent structural
similarity with 1k. The presence of a heteroatom or
branching in the side chain was found to be detrimental
for the reduction. This was revealed with substrates, viz.
a-methoxy and a-cyano acetophenones as well as a-tri-
¯uromethyl and cyclopropylphenyl ketones, which did not
undergo any bioconversion (data not shown). The ability of
the organism to reduce 1l (Table 1, entry 12), albeit in poor
yield, in contrast to cyclopropylphenyl ketone could be
attributed to the greater ¯exibility of the cyclohexyl group.
Scheme 2.
2±4). The yields, however, showed a gradual decrease
with increasing size of the halogens. In the case of substrates
possessing p-alkoxy groups, there was a large drop in the %
ee of the products (Table 2, entries 5, 6). In these cases,
possibly the 1M effect of the substituents outweighs their
2I effect leading to the above result. This was vindicated in
the case of the reduction of 2g (Table 2, entry 7), where the
substituent p-phenoxy group has a profound 2I effect. As
a consequence, its reduction showed a vastly improved
enantioselectivity, although due to the solubility constraints
of the substrate the yield was again poor. Considering the
modest 2I effect of the cyano substituent, reduction of 2h
gave the product with only 46% ee. Thus, it appears that
electronic effect of the substituents in the aromatic ring has a
de®nite role in the enantioselectivity of the reaction. Again,
among the various components, the mesomeric effect was
found to be more important than the inductive effect.
2.2. Reduction of 1-arylethanones
Next, the role of substituents in the aromatic moiety on the
course of the biotransformation was studied (Scheme 2). For
this, reduction of a series of 1-arylethanones was carried
out with R. arrhizus and the results are presented in Table
2. In this case, various para-substituted phenylethanones
(2a±p) were consistently converted to the corresponding
(S)-alcohols. In general, the para-substitution in the phenyl
ring improved the enantioselectivity of the reduction
(except in two cases) as compared to that for unsubstituted
substrate 1a. Introduction of electron withdrawing sub-
stituents is expected to assist the reaction. Indeed, the
p-halogen-substituted acetophenones 2a±d were reduced
with high enantioselectivity possibly due to the 2I effect
of the substituents. However, except for the ¯uoro
compound 2a (Table 2, entry 1), the effect of the differential
electronegativities of the halogen substitutions were
negligible on the % ees of the reaction (Table 2, entries
The minor role of the inductive effect was also manifested in
the reduction of the p-alkyl-substituted substrates (2i±n).
Reduction of these compounds showed a marked improve-
ment in % ee, which increased with the bulk of the alkyl
group. Here also, the enantioselectivity reached a plateau

2836
N. A. Salvi, S. Chattopadhyay / Tetrahedron 57 (2001) 2833±2839
the phenyl ring improved the % ees of the reduced product.
However, with 1I groups like alkyl, the steric factor was
more crucial.
For the determination of % ees, the carbinols were
converted12 into the corresponding MTPA esters with
(R)-MTPA. The % ees were then assayed by the H NMR
1
analyses of the respective esters. The con®gurations of the
carbinols 1a±d, 1m, 2a, 2c, 2e, 2i, 2j, 2p, 3a and 3b were
determined by comparison of their [a]D values with those
13a±f
1
reported.
Incidentally, in the H NMR spectra, the
methoxy resonances of the MTPA esters of the designated
compounds appeared as two singlets at d 3.44±3.48 (minor)
and 3.54±3.57 (major). Hence the down®eld NMR signal
could be attributed to those generated from the (S)-carbi-
nols. A similar observation was also reported earlier by
Brown et al.13d Since the MTPA esters of the rest of the
carbinols also showed the OMe resonances at d 3.54±3.57
as the major peak, they should also have (S)-con®guration.
The formation of (S)-alcohols could be rationalized by
Prelog's rule.14a,b
Scheme 3.
3. Experimental
after 2j (Table 2, entries 9±14) irrespective of the chain
length and the extent of branching in the alkyl group.
Presence of a phenyl group instead of an alkyl group at
the p-position (compound 2o) gave the product with
excellent ee (99%) due to the combined electronic and
size effects. The predominant steric effect on the enantio-
selectivity of the reduction was also obvious from the fact
that substrate 2p with a CF3 substiuent gave the correspond-
ing alcohol with much better % ee as compared to the ¯uoro-
compound 2a. However, in spite of increasing the
enantioselectivity, the increased molecular sizes of the
substituents, in general, led to poor yields in these transfor-
mations (Table 2, entries 9±16).
All the substrates (Aldrich, Fluka and Lancanster) were used
as received. (R)-(1)-a-Methoxy-a-tri¯uoromethylphenyl-
acetic acid (MTPA) was supplied by Aldrich. The fungus
R. arrhizus was obtained from the National Collection of
Industrial Microorganisms, National Chemical Laboratory,
Pune, India. The IR spectra as thin ®lms were scanned with
a Nicolet FT-IR model Impact 410 spectrophotometer. The
1H NMR spectra in CDCl3 were recorded with a Bruker
Ac-200 (200 MHz) spectrometer. The optical rotations
were recorded with a Jasco DIP 360 digital polarimeter.
The fungus from PDA slant was cultivated on 150 ml
sterilized modi®ed Czepak Dox medium in 500 mL
Erlenmeyer ¯asks at room temperature on a rotary shaker
(150 rpm).
2.3. Reduction of polyarylethanones
The utility of the organism in asymmetric reduction was
also probed using some polyarylethanones as the
substrates (Scheme 3). The reduction of the bulkier
substrates was, as expected, very slow. Some amount of
conversion could be obtained with the naphthylethanones
3a and 3b only, but 14 days of incubation were required
(Table 3). Bulkier substrates 3c±g did not show practically
any bioconversion due to their insolubility in the aqueous
medium. In this case also, the same sense of enantio-
preference was observed leading to the carbinols with (S)-
con®guration.
3.1. Preparation of microbial culture
The modi®ed Czepak Dox medium was prepared by mixing
FeSO4 (10 mg), K2HPO4 (50 mg), MgSO4 (250 mg), KCl
(0.5 g), KH2PO4 (0.95 g), NaNO3 (2.0 g), yeast extract
(0.5 g), cornsteep liquor (5 g) and glucose (8 g) in distilled
H2O (1 L). The medium was adjusted to pH 4.5±4.8 and
sterilized. The fungus from PDA slant was incubated in the
above medium (150 mL) and allowed to grow under static
conditions at 258C for 72 h.
Thus, the study demonstrated the applicability of the simple
microbial whole cell system of R. arrhizus for the bio-
transformation of a broad assortment of structurally
different arylalkanones. The reactivity and the enantio-
selectivity were governed mainly by the steric factors of
the groups ¯anking the reaction site. Increasing the size of
the two ¯anking groups by incorporating hydrophobic
groups (increasing the alkyl chain length or fusing aryl
group) led to a drop in conversion and an improvement in
the enantioselectivity. The polarity effect of the substituents
in the case of arylethanones was more drastic for 1M
groups. Presence of electron withdrawing substituents in
3.2. Microbial reduction of substrates
The substrates (100 mg) in EtOH (1 mL) were added to the
culture and shaken for the periods shown in the Tables.
Substrate and organism controls were also run simul-
taneously in each case. At the end of fermentation, the
mycelial mass was ®ltered from the culture medium. The
®ltrate was extracted with chloroform (3£50 mL), washed
with water (2£20 mL) and dried. Removal of solvent gave
an oily residue designated as the ®ltrate extract. The
mycelial mass was washed with hot acetone (3£50 mL)
and the extract concentrated in vacuo to give an oily residue.

N. A. Salvi, S. Chattopadhyay / Tetrahedron 57 (2001) 2833±2839
2837
This was taken into water and extracted with EtOAc
(3£50 mL), the organic extract washed with H2O and
brine and dried. Removal of solvent in vacuo gave the
mycelial extract as oil. Controls were also extracted in a
similar way. The transformed products and unchanged
substrates were isolated and puri®ed by preparative TLC
(silica gel G, EtOAc/Pet. Ether). All the products were
1H), 7.3±8.0 (m, 10H); MS m/z (rel. int. %): 122 (93.2), 105
(100), 77 (78.8), 51 (41.2).
3.2.8. 4l.13c White solid; [a]D ˆ228.1 (c 0.26, CHCl3); IR:
24
3330, 1070, 758, 702 cm21 1H NMR: d 1.5±2.3 (m,
;
partially D2O exchangeable, 12H), 4.26 (d, Jˆ7 Hz, 1H),
7.0±7.3 (m, 5H); MS m/z (rel. int. %): 190 (M1, 8.8), 172
(100), 157 (6.3), 143 (22.4), 141 (17.8), 129 (78.2), 127
(77.4), 117 (47.4), 115 (81.7), 107 (95), 104 (83.1), 91
(95.3).
1
characterized by IR and H NMR specroscopy. The major
amounts of the product alcohols were obtained from the
®ltrate extracts while the mycelial extracts provided the
unchanged substrates.
3.2.9. 4m.13h White solid; [a]D ˆ1106.7 (c 1.68, CHCl3);
24
3.2.1. 4a.13a±c Colourless liquid; [a]D ˆ243.7 (c 0.90,
23
IR: 3300, 1060, 697, 609 cm21; H NMR: d 2.2 (bs, D2O
1
1
CHCl3); IR: 3350, 1060, 749, 732 cm21; H NMR: d 1.46
exchangeable, 1H), 5.76 (s, 1H), 7.0±7.8 (m, 8H), 8.6 (d,
Jˆ8 Hz, 1H); MS m/z (rel. int. %): 185 (M1, 67.2), 167
(22.4), 155 (23.8), 139 (78.1), 108 (84.5), 83 (8.1), 79
(100), 77 (77.8), 63 (5.7), 51 (43.4).
(d, Jˆ6 Hz, 3H), 2.43 (bs, D2O exchangeable, 1H), 4.86 (q,
Jˆ6 Hz, 1H), 7.0±7.5 (m, 5H); MS m/z (rel. int. %): 122
(M1, 15.1), 107 (38.9), 104 (100), 78 (95.1), 63 (21.4), 51
(54.8).
3.2.10. 5a.13c Colourless liquid; [a]D ˆ238.7 (c 4.15,
24
3.2.2. 4b.13a±e Colourless liquid; [a]D ˆ244.4 (c 0.63,
24
CHCl3); IR: 3360, 1060, 845 cm21; H NMR: d 1.66 (d,
1
1
CHCl3); IR: 3380, 1060, 758, 697 cm21; H NMR: d 0.8
Jˆ6 Hz, 3H), 2.58 (bs, D2O exchangeable, 1H), 5.06 (q,
Jˆ6 Hz, 1H), 7.3±7.7 (m, 4H); MS m/z (rel. int. %): 122
(100), 101 (26.7), 96 (36.8), 83 (5.7), 75 (16.2), 63 (7.2), 57
(5.3).
(t, Jˆ6.2 Hz, 3H), 1.6±1.7 (m, 2H), 2.23 (bs, D2O
exchangeable, 1H), 4.46 (t, Jˆ6 Hz, 1H), 7.0±7.5 (m,
5H); MS m/z (rel. int. %): 136 (M1, 6.3), 118 (88.1), 117
(100), 107 (47.4), 91 (52.5), 79 (51.7), 77 (48), 65 (18.1), 63
(22.4), 51 (30.8).
3.2.11. 5b.13a,e Colourless liquid; [a]D ˆ248.4 (c 7.29,
27
1
CHCl3); IR: 3360, 1050, 898, 828 cm21; H NMR: d 1.43
24
3.2.3. 4c.13a,b,e White solid; [a]D ˆ244.9 (c 0.45, CHCl3);
(d, Jˆ6 Hz, 3H), 2.96 (bs, D2O exchangeable, 1H), 4.83 (q,
Jˆ6 Hz, 1H), 7.2±7.5 (m, 4H); MS m/z (rel. int. %): 156
(M1, 15.6), 141 (52.7), 138 (100), 121 (7.8), 113 (22.4), 103
(96.4), 87 (6.8), 77 (97.8), 63 (24.4), 51 (47.8).
IR: 3360, 1050, 755, 698 cm21 1H NMR: d 0.9 (t,
;
Jˆ6.2 Hz, 3H), 1.5±2.3 (m, 4H), 2.45 (bs, D2O exchange-
able, 1H), 4.86 (t, Jˆ6 Hz, 1H), 7.0±7.5 (m, 5H); MS m/z
(rel. int. %): 150 (M1, 11.8), 132 (87.1), 117 (100), 115
(89.7), 107 (83), 91 (84.8), 79 (77.2), 77 (78), 65 (35.3),
63 (34.4), 51 (56.3).
3.2.12. 5c.13c,e Pale yellow liquid; [a]D ˆ237.0 (c 5.0,
26
1
CHCl3); IR: 3340, 1060, 898, 828 cm21; H NMR: d 1.43
(d, Jˆ6 Hz, 3H), 2.87 (bs, D2O exchangeable, 1H), 4.78 (q,
Jˆ6 Hz, 1H), 7.0±7.7 (m, 4H); MS m/z (rel. int. %): 200
(M121, 6.1), 184 (100), 182 (53.4), 157 (12.4), 121 (9.3),
107 (55.7), 77 (56.8), 63 (21.7), 51 (21.1).
3.2.4. 4d.13a White solid; [a]D ˆ239.3 (c 0.57, CHCl3);
24
IR: 3380, 1060, 750, 699 cm21; 1H NMR: d 0.9 (t, Jˆ7 Hz,
3H), 1.5±1.7 (m, 6H), 2.03 (bs, D2O exchangeable, 1H),
4.43 (t, Jˆ6 Hz, 1H), 6.9±7.3 (m, 5H); MS m/z (rel. int.
%): 146 (85.1), 128 (14.4), 117 (100), 115 (93), 107 (57),
104 (79), 91 (83.4), 79 (42.6), 77 (47.1), 65 (26.3), 63 (24.2),
51 (31.8).
25
3.2.13. 5d. Pinkish solid; [a]D ˆ232.7 (c 5.99, CHCl3);
IR: 3335, 1060, 898, 879 cm21 1H NMR: d 1.33 (d,
;
Jˆ6 Hz, 3H), 2.43 (bs, D2O exchangeable, 1H), 4.76
(q, Jˆ6 Hz, 1H), 6.8±7.8 (m, 4H); MS m/z (rel. int.
%): 248 (M121, 8.7), 233 (14.8), 230 (100), 127 (33.4),
121 (6.3), 103 (77.2), 77 (99.2), 63 (16.8), 51 (40.8).
Anal. Calcd for C8H9OI: C 38.73, H 3.66; Found: C
38.70, H 3.60.
24
3.2.5. 4e. White solid; [a]D ˆ235.0 (c 0.88, CHCl3); IR:
1
3360, 1060, 755, 735 cm21; H NMR: d 0.93 (t, Jˆ7 Hz,
3H), 1.4±1.6 (m, 8H), 2.0 (bs, D2O exchangeable, 1H), 4.91
(t, Jˆ6 Hz, 1H), 7.1±7.4 (m, 5H); MS m/z (rel. int. %): 160
(81.1), 131 (16.8), 126 (16.8), 117 (100), 115 (95.2), 107
(76.7), 104 (95.9), 91 (81.8). Anal. Calcd for C12H18O: C
80.85, H 10.18; Found: C 81.10, H 10.10.
3.2.14. 5e.13c,d Colourless liquid; [a]D ˆ21.1 (c 4.7,
27
1
CHCl3); IR: 3380, 1060, 832 cm21; H NMR: d 1.40 (d,
Jˆ6 Hz, 3H), 2.26 (bs, D2O exchangeable, 1H), 3.72 (s,
3H), 4.83 (q, Jˆ6 Hz, 1H), 6.7±7.1 (m, 4H);. MS m/z (rel.
int. %): 134 (100), 119 (82.4), 103 (81.4), 91 (99.6), 77
(17.8), 65 (68.6), 51 (21.6).
24
3.2.6. 4f. White solid; [a]D ˆ229.2 (c 0.89, CHCl3); IR:
1
3350, 1060, 758, 705 cm21; H NMR: d 0.9 (t, Jˆ6.2 Hz,
3H), 1.4±1.6 (m, 10H), 1.95 (bs, D2O exchangeable, 1H),
4.76 (t, Jˆ6 Hz, 1H), 7.2±7.4 (m, 5H); MS m/z (rel. int. %):
192 (M1, 6.8), 174 (41.2), 145 (6.4), 131 (24.8), 125 (25.1),
117 (100), 115 (51), 107 (52.8), 104 (99.8), 91 (46.2). Anal.
Calcd for C13H20O: C 81.20, H 10.48; Found: C 81.44, H
10.60.
24
3.2.15. 5f. Pale yellow solid; [a]D ˆ20.2 (c 6.30, CHCl3);
1
IR: 3400, 1060, 898, 836 cm21; H NMR: d 1.43±1.46
(merged d and t, 6H), 2.0 (bs, D2O exchangeable, 1H),
4.03 (q, Jˆ7 Hz, 2H), 4.83 (q, Jˆ6 Hz, 1H), 6.8±7.3 (m,
4H); MS m/z (rel. int. %): 148 (79.8), 120 (100), 105 (5.3),
103 (6.1), 91 (79.8), 77 (22.4), 65 (56.3), 63 (26), 51 (18.7).
Anal. Calcd for C10H14O2: C 72.26, H 8.49; Found: C 72.50,
H 8.37.
3.2.7. 4k.13b White solid; [a]D ˆ10.08 (c 2.56, CHCl3);
24
1
IR: 3330, 1070, 758, 702 cm21; H NMR: d 2.3 (bs, D2O
exchangeable, 12H), 3.33 (d, Jˆ6 Hz, 2H), 5.23 (t, Jˆ6 Hz,

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23
3.2.16. 5g. Pale yellow liquid; [a]D ˆ240.0 (c 0.81,
Jˆ6 Hz, 1H), 7.0±7.3 (m, 4H); MS m/z (rel. int. %): 204
(M1, 6.2), 189 (31.2), 186 (83.1), 143 (92.8), 130 (100), 128
(91.8), 117 (92.1), 115 (77.3), 104 (30.9), 91 (51.9), 83
(21.4), 77 (31.2), 67 (8.8), 65 (14.7), 63 (12.1), 51 (12.4).
Anal. Calcd for C14H20O: C 82.30, H 9.87; Found: C 82.16,
H 10.08.
1
CHCl3); IR: 3380, 1060, 898, 845 cm21; H NMR: d 1.53
(d, Jˆ6 Hz, 3H), 2.16 (bs, D2O exchangeable, 1H), 5.03 (q,
Jˆ6 Hz, 1H), 7.1±7.6 (m, 9H); MS m/z (rel. int. %): 196
(100), 181 (9.8), 177 (8.7), 167 (76.7), 153 (56.1), 141
(24.2), 139 (11.2), 128 (10.4), 120 (25.1), 115 (27.8), 102
(30.6), 98 (6.4), 94 (5.7), 91 (79.3), 77 (98.6), 65 (81.3), 51
(87). Anal. Calcd for C14H14O2: C 78.48, H 6.59; Found: C
78.64, H 6.47.
28
3.2.24. 5o. White solid; [a]D ˆ243.7 (c 0.75, CHCl3); IR:
1
3320, 1060, 750 cm21; H NMR: d 1.8 (d, Jˆ6 Hz, 3H),
2.30 (bs, D2O exchangeable, 1H), 5.23 (q, Jˆ6 Hz, 1H),
7.4±8.0 (m, 9H); MS m/z (rel. int. %): 198 (M1, 7.5), 183
(12.6), 180 (100), 178 (32.1), 165 (22.4), 152 (29.8), 115
(11.8), 102 (9.9), 89 (12.1), 77 (23.4), 63 (11.1), 51 (11.7).
Anal. Calcd for C14H14O: C 84.81, H 7.12; Found: C 84.69,
H 7.31.
3.2.17. 5h.13g Pale yellow liquid; [a]D ˆ240.2 (c 2.23,
25
1
CHCl3); IR: 3410, 1070, 898, 845 cm21; H NMR: d 1.25
(d, Jˆ6 Hz, 3H), 1.82 (bs, D2O exchangeable, 1H), 4.72 (q,
Jˆ6 Hz, 1H), 7.0±7.3 (m, 4H). MS m/z (rel. int. %): 147
(M1, 8.1), 132 (81), 104 (100), 77 (42), 63 (14.7), 51 (27.8).
3.2.25. 5p.13c Colourless liquid; [a]D ˆ231.5 (c 5.49,
22
3.2.18. 5i.13a Colourless liquid; [a]D ˆ245.3 (c 5.81,
22
1
CHCl3); IR: 3350, 1070, 898, 845 cm21; H NMR: d 1.56
1
CHCl3); IR: 3390, 1060, 878, 819 cm21; H NMR: d 1.45
(d, Jˆ6 Hz, 3H), 5.03 (q, Jˆ6 Hz, 1H), 7.3±7.8 (m, 4H);
MS m/z (rel. int. %): 175 (62.4), 172 (17.4), 151 (8.4), 147
(15.4), 145 (17.7), 127 (100), 103 (18.1), 95 (7.1), 77 (21),
69 (22.8), 63 (8.1), 51 (17).
(d, Jˆ6 Hz, 3H), 2.34 (s, 3H), 4.5 (bs, D2O exchangeable,
1H), 4.93 (q, Jˆ6 Hz, 1H), 7.0±7.6 (m, 4H); MS m/z (rel.
int. %): 136 (M1, 17.1), 121 (47.4), 118 (82.4), 117 (100),
115 (51.4), 103 (14.8), 93 (49.8), 91 (94.5), 79 (12.4), 77
(38.6), 65 (32.3), 63 (21.9), 51 (18).
3.2.26. 6a.13b,c,e,g Pinkish solid; [a]D ˆ253.6 (c 1.80,
27
1
CHCl3); IR: 3370, 1060, 898, 810 cm21; H NMR: d 1.56
23
3.2.19. 5j. Colourless liquid; [a]D ˆ244.9 (c 5.98,
1
CHCl3); IR: 3360, 1060, 898, 836 cm21; H NMR: d 1.1±
(d, Jˆ6 Hz, 3H), 2.64 (bs, D2O exchangeable, 1H), 5.06 (q,
Jˆ6 Hz, 1H), 7.4±7.55 (3H), 7.7±7.83 (m, 4H); MS m/z
(rel. int. %): 172 (M1, 16.2), 157 (15.9), 154 (100), 139
(10.7), 128 (64.8), 115 (16.2), 101 (11.4), 87 (8.6), 77
(32), 76 (57.5), 63 (26.1).
1.6 (merged d and t, 6H), 2.63 (q, Jˆ6 Hz, 2H), 2.8 (bs, D2O
exchangeable, 1H), 4.86 (q, Jˆ6 Hz, 1H), 7.0±7.5 (m, 4H);
MS m/z (rel. int. %): 150 (M1, 10.2), 135 (22.4), 132 (64.4),
121 (6.8), 117 (100), 115 (47.8), 105 (12.4), 103 (12.1), 91
(42.6), 79 (54.6), 65 (16.8), 63 (16.1), 51 (9.8). Anal. Calcd
for C10H14O: C 79.96, H 9.39; Found: C 80.14, H 9.22.
3.2.27. 6b.13c,f,g White solid; [a]D ˆ247.4 (c 1.64,
23
1
CHCl3); IR: 3365, 1060, 879, 809 cm21; H NMR: d 1.46
23
3.2.20. 5k. Colourless liquid; [a]D ˆ245.8 (c 3.34,
(d, Jˆ6 Hz, 3H), 2.16 (bs, D2O exchangeable, 1H), 5.03 (q,
Jˆ6 Hz, 1H), 7.0±7.3 (5H), 7.7±7.83 (m, 2H); MS m/z (rel.
int. %): 172 (M1, 50.6), 155 (83), 154 (57), 127 (100), 115
(16.2), 101 (11.4), 87 (7.2), 77 (32), 76 (47.3), 63 (34.2).
1
CHCl3); IR: 3370, 1060, 898, 8368 cm21; H NMR: d 1.2
(d, Jˆ7 Hz, 6H) 1.45 (d, Jˆ6 Hz, 3H), 1.63 (bs, D2O
exchangeable, 1H), 2.74±2.81 (m, 1H), 4.67 (q, Jˆ6 Hz,
1H), 7.1±7.7 (m, 4H); MS m/z (rel. int. %): 149 (8.8), 146
(22.2), 131 (100), 129 (15.4), 115 (21.6), 103 (14.7), 91
(58.4), 77 (24.8), 65 (12.8), 63 (12.2), 51 (11.1). Anal.
Calcd for C11H16O: C 80.44, H 9.82; Found: C 80.26, H
9.88.
27
3.2.28. 6c. Light yellow solid; [a]D ˆ243.2 (c 0.24,
1
CHCl3); IR: 3320, 1060, 836, 740 cm21; H NMR: d 1.66
(d, Jˆ6 Hz, 3H), 2.03 (bs, D2O exchangeable, 1H), 4.03 (s,
2H), 5.14 (q, Jˆ6 Hz, 1H), 7.3±8.0 (m, 7H); MS m/z (rel.
int. %): 210 (M1, 9.3), 192 (100), 165 (81.8), 152 (6.4), 139
(8.1), 115 (7.2), 96 (13.4), 94 (25.3), 82 (17.1), 63 (9.6).
Anal. Calcd. for C15H14O: C 85.68, H 6.71; Found: C 85.50,
H 6.95.
24
3.2.21. 5l. White solid; [a]D ˆ238.8 (c 1.54, CHCl3); IR:
1
3355, 1060, 610 cm21; H NMR: d 1.26 (s, 9H), 1.44 (d,
Jˆ6 Hz, 3H), 1.56 (bs, D2O exchangeable, 1H), 4.88 (q,
Jˆ6 Hz, 1H), 7.2±7.4 (m, 4H); MS m/z (rel. int. %): 163
(11.42), 160 (24), 145 (100), 128 (14.8), 117 (48.2), 115
(19.3), 105 (22.2), 103 (9.8), 91 (26.4), 77 (22.1), 65
(8.8), 63 (9.1), 51 (14.8). Anal. Calcd for C12H18O: C
80.85, H 10.18; Found: C 80.76, H 10.10.
References
1. Singh, V. K. Synthesis 1992, 605±617.
2. (a) Jones, J. B.; Beck, J. F. In Application of Biochemical
Systems in Organic Chemistry. Part 1; Jones, J. B., Sih,
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23
3.2.22. 5m. Colourless liquid; [a]D ˆ238.6 (c 0.39,
1
CHCl3); IR: 3360, 1070, 941, 608 cm21; H NMR: d 1.3±
2.0 (m, 10H), 2.63 (t, Jˆ7 Hz, 2H), 2.7 (bs, D2O exchange-
able, 1H), 4.86 (q, Jˆ6 Hz, 1H), 7.2±7.6 (m, 4H); MS m/z
(rel. int. %): 160 (22.1), 117 (100), 115 (24.8), 91 (27.3), 77
(11.8), 65 (7.8), 51 (8.1). Anal. Calcd for C12H18O: C 80.85,
H 10.18; Found: C 80.68, H 10.32.
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23
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