Enantioselective bioreduction of (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime)

Article abstract of DOI:10.1016/S0957-4166(00)00163-4

The baker's yeast reduction of (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime), PhC(O)C(NOMe)R (R=Me, Et, n-Pr, n-Bu), gave the corresponding optically active alcohols PhCH₂OHC(NOMe)R in 88-99% enantiomeric excess and 48-75% chemical yield. The

Full text of DOI:10.1016/S0957-4166(00)00163-4

Tetrahedron: Asymmetry 11 (2000) 2107±2115
Enantioselective bioreduction of (E)-1-phenyl-1,2-alkanedione
2-(O-methyloxime)
Olyr C. Kreutz, Renata C. M. Segura, J. Augusto R. Rodrigues and Paulo J. S. Moran*
Â
Instituto de Quõmica, Universidade Estadual de Campinas, C.P. 6154-13083-970 Campinas, SP Brazil
Received 2 March 2000; accepted 13 April 2000
Abstract
The baker's yeast reduction of (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime), PhC(O)C(NOMe)R
(R=Me, Et, n-Pr, n-Bu), gave the corresponding optically active alcohols PhCH2OHC(NOMe)R in 88±
99% enantiomeric excess and 48±75% chemical yield. The R con®guration was proposed for these alcohols
based on circular dichroism analysis. Only the phenylglyoxal O-methylaldoxime (R=H) gave poor
enantiomeric excess (65%) and chemical yield (14%). These compounds are potential chiral building blocks
for the stereoselective synthesis of norephedrine analogs. # 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
The stereoselective synthesis of enantiomerically pure 1,2-aminoalcohols is important due to
their utilisation as chemotherapeutic drugs, chiral auxiliaries and chiral building blocks in organic
synthesis.1,2 Ephedrine, which is extracted from various species of Ephedra, acts on the sympathetic
nervous system. In addition, the analogs of the natural (^)-(1R,2S)-ephedrine and (+)-(1S,2S)-
pseudoephedrine are an important class of bioactive compounds. The enantioselective synthesis
of norephedrine or norpseudoephedrine has been performed by organolithium addition to aldehyde
dimethylhydrazones,3 Friedel±Crafts reaction of l-amino acid chloride,4 by reductions of esters
of natural amino acid blocked in the form of cyanoenamine,5 by a chiral intermediate of chloram-
phenicol synthesis,6 reaction of benzaldehyde and acetyl±CoA promoted by brewer's yeast,7 from
optically active cyanohydrins,8,9 asymmetric a-amination of ketone enolates by homochiral a-
chloro-a-nitroso reagents10 and baker's yeast reduction of a-azidopropiophenone.11
Recently, the reduction of (E)-1-phenyl-1,2-propanedione 2-(O-methyloxime) by baker's yeast
(Saccharomyces cerevisiae) was used as a key step in the enantioselective synthesis of (^)-(1R,2S)-
norephedrine and (^)-(1R,2R)-norpseudoephedrine.12 In this work, we apply this methodology with
phenylglyoxal O-methylaldoxime, 2a, and several (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime),
* Corresponding author. Fax: 55-19-7883023; e-mail: moran@iqm.unicamp.br
0957-4166/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(00)00163-4

2108
O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
PhC(O)C(NOMe)R, 2c (R=Et), 2d (R=n-Pr) and 2e (R=n-Bu) in the preparation of chiral
building blocks for the synthesis of norephedrine analogs. Comments are made on the in¯uence
of the size of alkyl moiety in the baker's yeast reduction of (E)-1-phenyl-1,2-alkanedione 2-(O-
methyloxime).
2. Results and discussion
The appropriate alkyl phenyl ketones were nitrosated by Slater's method13 to give the (E)-1-
phenyl-1,2-alkanedione 2-oximes that were methylated by a modi®ed Buehler's method14
(Scheme 1). While the nitrosation of alkyl phenyl ketones gave the (E)-1-phenyl-1,2-alkanedione
2-oxime, a mixture of Z- and E-isomers was obtained by reaction of the appropriate 1-phenyl-
1,2-alkanedione with methoxylamine hydrochloride. The evidence for the E-isomer is based on
the 13C NMR spectrum comparison of a mixture of Z- and E-isomers and a sample of a pure
E-isomer.15 The observed up®eld shift (see Table 1) due to the steric compression between the
methyl carbon syn to the OH or OMe groups (as well as for the methylene carbon has previously
been described for the ketone oximes).16,17 Down®eld shifts of 3.6±3.7 ppm were observed for the
C1 signals of the E-isomers 2b±e.
Scheme 1.
Table 1
13C NMR chemical shifts for C1, C2 and C3 of (Z)- and (E)-1-phenyl-1,2-alkanedione2-(O-methyloxime)

O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
2109
The ketone function of phenylglyoxal O-methylaldoxime 2a and (E)-1-phenyl-1,2-alkanedione
2-(O-methyloxime) 2b±e was reduced by baker's yeast yielding the corresponding optically active
alcohols 3a±e (Scheme 2). The optimised reaction times, presented in Table 2, were determined by
gas chromatography analysis of samples that were withdrawn from the reaction mixture at
appropriate intervals. The reactivities of 2a±e decrease with the increase of the size of alkyl moiety.
Scheme 2.
Table 2
Baker's yeast reduction of (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime)
While the O-methyloximes 3c±e were stable in the bioreduction medium, 3a and 3b undergo
subsequent reactions. For example, the O-methyloxime 3b was converted into (^)-(1R,2S)-1-
phenyl-1,2-propanediol, 4 (R=Me), after 120 h12 (Scheme 3). It is reasonable to suppose that the
transformation of 3 into 4 should involve two steps: a hydrolysis of the O-methyloxime function
giving a ketone followed by the stereoselective reduction of this ketone giving the optically active
diol.18 The diol 4 (R=Me) is generally obtained when 1-phenyl-1,2-propanedione is subjected to
baker's yeast reduction without pH control.19,20 These two steps seem to be mediated by baker's
yeast. The hydrolysis of the O-methyloxime function is a critical step and seems to be dependent
on the size of the R group (Scheme 3). In addition, we were unable to perform the chemical
deoximation of 3b12 using the available methodologies for oximes.21 24
Scheme 3.

2110
O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
The con®guration of O-methyloxime 3b was determined as R by diastereoselective reduction
of 3b using LiAlH4 to obtain the (^)-(1R,2S)-norephedrine with ee >82% and (^)-(1R,2R)-
norpseudoephedrine with 93% ee, respectively, in a 4:1 ratio.12 The circular dichroism (CD)
spectra of O-methyloximes 3b±e show a large and positive Cotton e€ect (CE) at l=221±224 nm
1
and also a positive CE of Lb determined by vibronic borrowing25,26 from benzene transitions
at wavelengths 240±270 nm (Fig. 1). Due to the similarity of CE spectra we can assume that
the O-methyloximes 3c±e have the same con®guration as 3b, i.e. R con®guration. Applying the
1
empirical sector rule,27 which correlate the sign of the Lb CEs and the absolute con®guration
of a chiral centre contiguous to the benzene ring, we can state that the sequences for summation
of contributions27 to the 1Lb CEs are ±C(ˆNOMe)R>±OH as shown in Fig. 2.
Figure 1. CD spectra of 3b±e obtained by baker's yeast reduction of (E)-2b±e
Figure 2. Empirical sector rule (1Lb transition)1 for chiral benzylic derivatives with OH and C(ˆNOMe)R groups
The speci®c rotation values of O-methyloximes 3c±e are similar (‰ꢀŠ2D0=^105 to ^144). Only 3a
shows a slightly positive rotation and poor enantiomeric excess (65%). The enantiomeric excesses
of the O-methyloximes 3b±e (88±99%) increase and the chemical yields decrease with the size of
alkyl moiety.

O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
2111
3. Conclusion
The baker's yeast reduction of the ketone function of (E)-1-phenyl-1,2-alkanedione 2-(O-methyl-
oxime) a€ords the corresponding (E)±(R)-1-hydroxy-1-phenyl-2-alkanone 2-(O-methyloxime) with
reasonable yields and good enantiomeric excesses. A substrate selectivity, which is in¯uenced by the
size of R group, was observed in the reduction of the ketone function and also in the subsequent
reaction giving the corresponding diol.
4. Experimental
4.1. General
Melting points were measured on a Microquimica MQAFP-301 apparatus and are uncorrected.
IR spectra were recorded on a Perkin±Elmer 1600 FT spectrophotometer. NMR spectra were
recorded on a Bruker AC 300P or Varian Gemini 300 spectrometer with CDCl3 as solvent and
TMS as an internal standard. CD spectra were recorded on a JASCO J-720 spectropolarimeter.
Gas chromatography analyses were performed on a HP 5890 chromatograph, with a HP-5
column (crosslinked 5% Ph Me Silicone, ID 0.53 mm, 30 m length). Enantiomeric excesses were
determined by GC analysis using a chiral column [stationary phase: heptakis-(2,6-methyl-3-
penthyl)-b-cyclodextrine]. Chromatographical column separations were performed with Silica
gel-60. Mass spectra were obtained on a Shimadzu CGMS-QP5000 spectrometer and high-
resolution mass spectra were obtained on a Fisons VG Autoespec Varian. Speci®c rotations
were measured on a Carl Zeis Polamat A polarimeter. Commercially available chemicals and
solvents were used without further puri®cation. Commercially available dry baker's yeast from
N. V. Algist-Bruggeman S. A. was used in this work. The compounds 2b and 3b were described
previously.12
4.2. General procedure for the preparation of (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime)
The appropriated alkyl phenyl ketone, nitrosated by Slater's method,12 was methylated by the
following modi®ed Buehler's method:14 Ag2O (3.2 g, 13.8 mmol) was slowly added with stirring
to a solution of (E)-1-phenyl-1,2-alkanedione 2-oxime (12.3 mmol) and MeI (8.7 mL, 61.5 mmol)
in 15 mL of CH2Cl2, and cooled with an ice±water bath. After 0.5 h of reaction, the precipitate
was ®ltered o€ and washed with CH2Cl2. The CH2Cl2 was evaporated from the ®ltrate yielding
the corresponding (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime).
4.3. General procedure for the preparation of a mixture of (E)- and (Z)-1-phenyl-1,2-alkanedione
2-(O-methyloxime)
The title isomer mixture was obtained following the modi®ed Denmark method.28 A solution
of the appropriate 1-phenyl-1,2-alkanedione (1.5 equiv.) in glacial acetic acid (0.33 M) was treated
with potassium acetate (3.0 equiv.) and methoxylamine hydrochloride (3.0 equiv.). This mixture
was stirred for 1 h at room temperature, poured into water and the resulting solution was

2112
O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
neutralised with a saturated solution of sodium bicarbonate. The products were extracted with
ethyl acetate, dried with magnesium sulphate and the solvent evaporated at reduced pressure.
4.4. (E)-1-Phenyl-1,2-butanedione 2-oxime 1c
Following Buehler's general procedure, compound 1c was obtained as an orange oil in 85%
yield. IR (®lm): 3362, 2977, 2877, 1654, 1597, 1449, 877 cm^1; MS (70 eV) m/z 177 (M+, 2%), 160
1
(5), 105 (100), 77 (57), 51 (29); H NMR (300 MHz, CDCl3) ꢁ: 1.12 (t, 3H), 2.71 (q, 2H), 7.40±
7.48 (m, 2H), 7.56±7.62 (m, 1H), 7.86±7.90 (m, 2H), 9.50 (bs, OH); 13C NMR (75 MHz, CDCl3)
ꢁ: 10.1, 17.9, 128.8, 130.1, 132.8, 136.5, 160.9, 192.0; HRMS found: m/z 177.0794; calcd for
C10H11NO2 [M]+: 177.0790.
4.5. (E)-1-Phenyl-1,2-pentanedione 2-oxime 1d
Following Buehler's general procedure, compound 1d was obtained as an orange oil in 79%
yield. IR (®lm): 3251, 3038, 2961, 1635, 1576, 1447, 1017, 728, 694 cm^1; MS (70 eV) m/z 191 (M+,
1
0.8%), 174 (12), 105 (65), 77 (100), 51 (65); H NMR (300 MHz, CDCl3) ꢁ: 0.96 (t, 3H), 1.58
(m, 2H), 2.70 (t, 2H), 7.41±7.45 (m, 2H), 7.53±7.58 (m, 1H), 7.85±7.88 (m, 2H), 8.76 (bs, OH);
13C NMR (75 MHz, CDCl3) ꢁ: 14.3, 19.3, 26.4, 128.7, 130.7, 133.4, 137.3, 160.8, 192.8; HRMS
found: m/z 191.0948; calcd for C11H13NO2 [M]+: 191.0946.
4.6. (E)-1-Phenyl-1-2-hexanedione 2-oxime 1e
Following Buehler's general procedure, compound 1e was obtained as an orange oil in 72%
yield. IR (®lm): 3349, 2960, 2932, 1708, 1664, 1452, 1281, 1217, 1004, 713 cm^1; MS (70 eV) m/z
205 (M+, 2%), 188 (7), 105 (100), 84 (19), 77 (76), 51 (40), 41 (48); 1H NMR (300 MHz, CDCl3) ꢁ:
0.91 (t, 3H), 1.33±1.43 (m, 2H), 1.47±1.57 (m, 2H), 2.71 (t, 2H), 7.34±7.48 (m, 2H), 7.53±7.58
(m, 1H), 7.85±7.90 (m, 2H); 13C NMR (75 MHz, CDCl3) 13.8, 23.0, 24.3, 28.0, 128.7, 130.8,
133.4, 137.2, 160.9, 192.8; HRMS found: m/z 205.1106; calcd for C12H15NO2 [M]+: 205.1103.
4.7. Phenylglyoxal (O-methylaldoxime) 2a
Following the general procedure, compound 2a was obtained as an orange oil in 96% yield
from the corresponding oxime. IR (®lm): 3060, 2941, 1651, 1588, 1446, 1327, 1277, 1038, 1019,
1
695, 640 cm^1; MS (70 eV) m/z: 163 (M+, 4%), 105 (100), 77 (62), 51 (47); H NMR (300 MHz,
CDCl3) ꢁ: 4.09 (s, 3H), 7.36±7.56 (m, 2H), 7.57±7.63 (m, 1H), 7.95 (s, 1H), 8.11±8.30 (m, 2H);
13C NMR (75 MHz, CDCl3) ꢁ: 63.7, 128.9, 130.6, 133.9, 136.4, 144.6, 188.9.
4.8. (E)-1-Phenyl-1,2-butanedione 2-(O-methyloxime) 2c
Following the general procedure, compound 2c was obtained as an orange oil in 91% yield
from the corresponding oxime. IR (®lm): 2973, 2935, 1661, 1597, 1040, 861, 720 cm^1; MS (70 eV)
1
m/z: 191 (M+, 2%), 160 (22), 105 (100), 77 (52), 51 (33); H NMR (300 MHz, CDCl3, TMS) ꢁ:
1.11 (t, 3H), 2.68 (q, 2H), 4.01 (s, 3H), 7.39±7.46 (m, 2H), 7.51±7.58 (m, 1H), 7.95±7.99 (m, 2H);
13C NMR (75 MHz, CDCl3, TMS) ꢁ: 10.1, 18.2, 62.3, 128.1, 130.7, 132.8, 136.9, 160.0, 191.5;
HRMS found: m/z 191.0943; calcd for C11H13NO2 [M]+: 191.0946.

O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
2113
4.9. (E)-1-Phenyl-1,2-pentanedione 2-(O-methyloxime) 2d
Following the general procedure, compound 2d was obtained as an orange oil in 93% yield
from the corresponding oxime. IR (®lm): 3058, 2963, 2937, 1660, 1598, 1446, 1043, 714 cm^1; MS
1
(70 eV) m/z: 205 (M+, 2%), 174 (12), 105 (100), 77 (88), 58 (12), 51 (59); H NMR (300 MHz,
CDCl3, TMS) ꢁ: 0.96 (t, 3H), 1.57 (m, 2H), 2.67 (m, 2H), 4.00 (s, 3H), 7.39±7.44 (m, 2H), 7.51±
7.53 (m, 1H), 7.95±7.98 (m, 2H); 13C NMR (75 MHz, CDCl3, TMS) ꢁ: 13.9, 19.2, 26.5, 62.8,
128.0, 130.7, 132.7, 136.9, 159.0, 191.6; HRMS found: m/z 205.1103; calcd for C12H15NO2 [M]+:
205.1103.
4.10. (E)-1-Phenyl-1-2-hexanedione 2-(O-methyloxime) 2e
Following the general procedure, compound 2e was obtained as an orange oil in 92% yield
from the corresponding oxime. IR (®lm): 3060, 2959, 2936, 1663, 1596, 1451, 1220, 1043, 906, 719
1
cm^1; MS (70 eV) m/z: 219 (M+, 2%), 188 (20), 105 (100), 77 (71), 51 (33); H NMR (300 MHz,
CDCl3, TMS) ꢁ: 0.91 (t, 3H), 1.38 (m, 2H), 1.48 (m, 2H), 2.69 (t, 2H), 4.02 (s, 3H), 7.40±7.45
(m, 2H), 7.50±7.57 (m, 1H), 7.94±7.98 (m, 2H); 13C NMR (75 MHz, CDCl3, TMS) ꢁ: 13.9, 23.1,
24.8, 28.7, 63.2, 128.5, 131.1, 133.1, 137.3, 159.6, 192.0; HRMS found: m/z 219.1257; calcd for
C13H17NO2 [M]+: 219.1259.
4.11. General procedure for the reduction of (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime) by
free baker's yeast
O-Methyloxime (3 mmol) dissolved in 5 mL of ethanol was added with stirring at 30ꢀC to a
suspension of 10 g of dry baker's yeast and 30 g of sucrose in 1 L of aqueous solution of 2% KCl.
After continuous stirring for the speci®ed time (see Table 2), the reaction mixture was saturated
with sodium chloride and the product was extracted with chloroform in a liquid±liquid continuous
extractor during 72 h. After solvent evaporation, the residue was subjected to a chromatography
column with hexane:ethyl acetate (5:1) as eluent in order to separate the product and the
unreacted O-methyloxime.
4.12. Yeast immobilisation29
Dry baker's yeast (10 g) was added to a suspension of 30 g of Montmorillonite K10 in 1 L of
water and then the resultant suspension was gently shaking for 1.5. After vacuum ®ltration the
immobilised baker's yeast (IMBY) was suspended in 1 L of an aqueous solution of 2% KCl.
4.13. General procedure for the reduction of (E)-1-phenyl-1,2-alkanedione 2-(O-methyloxime) by
IMBY
Sucrose (30 g) was added to the previous prepared suspension of IMBY. After 30 min of
mechanical stirring at 30ꢀC, the O-methyloxime (3.0 mmol) dissolved in 5 mL of ethanol was
added and the stirring continued for the additional speci®ed time (see Table 2). The IMBY was then
®ltered o€ and the ®ltrate was extracted with ethyl acetate. After solvent evaporation, the residue
was subjected to the same procedure described above.

2114
O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
4.14. Baker's yeast reduction of phenylglyoxal (O-methylaldoxime) 2a
Following the general procedure using free baker's yeast, compound 3a was isolated after 6 h
of reaction as an oil in 14% yield. ‰ꢀŠ2D0=+3.8 (c 4.5, CHCl3), 62% ee; IR (®lm): 3398, 3064, 3031,
2960, 2937, 1686, 1492, 1451, 1034, 700 cm^1; MS (70 eV) m/z: 149 (0.8), 136 (100), 107 (21), 105
(41), 91 (9), 79 (85), 77 (92), 60 (94), 51 (52); 1H NMR (300 MHz, CDCl3) ꢁ: 3.87 (s, 3H), 5.31 (d,
1H), 7.32±7.39 (m, 5H), 7.45 (d, 1H); 13C NMR (75 MHz, CDCl3) ꢁ: 62.0, 71.8, 126.6, 128.5,
129.0, 140.0, 150.7.
4.15. Baker's yeast reduction of (E)-1-phenyl-1,2-butanedione 2-(O-methyloxime) 2c
Following the general procedure using IMBY, compound 3c was isolated after 24 h of reaction
as an oil in 73% yield. ‰ꢀŠ2D0=^105 (c 1.3, CHCl3), 92% ee; IR (®lm): 3410, 3063, 3030, 2974,
2939, 1445, 1188, 1046, 907, 703 cm^1; MS (70 eV) m/z: 193 (M+, 2%), 164 (3), 132 (11), 107 (57),
77 (100), 37 (77); 1H NMR (500 MHz, CDCl3, TMS) ꢁ: 0.82 (t, 3H), 1.97±2.01 (m, 1H), 2.18±2.32
(m, 1H), 3.90 (s, OH), 3.93 (s, 3H), 5.18 (d, 1H), 7.32 (m, 5H); 13C NMR (125 MHz, CDCl3,
TMS) ꢁ: 10.4, 19.9, 62.2, 74.6, 127.7, 128.7, 129.0, 140.5, 161.6. HRMS found: m/z 193.1103;
calcd for C11H15NO2 [M]+: 193.1103.
4.16. Baker's yeast reduction of (E)-1-phenyl-1,2-pentanedione 2-(O-methyloxime) 2d
Following the general procedure using IMBY, compound 3d was isolated after 72 h of reaction
as an oil in 52% yield. ‰ꢀŠ2D0=^137 (c 1.3, CHCl3), 98% ee; IR (®lm): 3426, 2962, 2933, 1662,
1451, 1046, 907, 703 cm^1; MS (70 eV) m/z: 207 (M+, 4%), 178 (13), 146 (31), 107 (100), 77 (67),
51 (36), 41 (55); 1H NMR (500 MHz, CDCl3, TMS) ꢁ: 0.80 (t, 3H), 1.17±1.41 (m, 2H), 1.68 (s br,
OH), 1.83±1.93 (m, 1H), 2.18±2.29 (m, 1H), 3.92 (s, 3H), 5.16 (d, 1H), 7.28±7.38 (m, 5H); 13C
NMR (125 MHz, CDCl3, TMS) ꢁ: 14.3, 19.4, 28.6, 62.1, 74.9, 127.4, 128.4, 128.8, 140.4, 160.1;
HRMS found: m/z 207.1258; calcd for C12H17NO2 [M]+: 207.1259.
4.17. Baker's yeast reduction of (E)-1-phenyl-1,2-hexanedione 2-(O-methyloxime) 2e
Following the general procedure using free baker's yeast, compound 3e was isolated after 72 h
of reaction as an oil in 48% yield. ‰ꢀŠ2D0=^144 (c 1.3, CHCl3), ee >99%; IR (®lm): 3373, 3063,
2957, 2953, 1682, 1595, 1450, 1254, 1041, 714 cm^1; MS (70 eV) m/z: 221 (M+, 3%), 192 (10), 160
1
(15), 116 (27), 107 (91), 77 (100), 54 (36), 51 (52), 43 (90), 41 (98); H NMR (300 MHz, CDCl3,
TMS) ꢁ: 0.79 (t, 3H), 1.15±1.27 (m, 4H), 1.85±1.90 (m, 1H), 2.19±2.28 (m, 1H), 3.91 (s, 3H), 3.98
(d, 1H), 5.16 (d, 1H), 7.29±7.37 (m, 5H); 13C NMR (75 MHz, CDCl3, TMS) ꢁ: 13.6, 22.9, 26.3,
28.0, 62.0, 74.8, 127.4, 128.4, 128.8, 140.4, 160.4; HRMS found: m/z 221.1417; calcd for
C13H19NO2 [M]+: 221.1416.
Acknowledgements
We are grateful to FAPESP and CNPq for ®nancial assistance.

O. C. Kreutz et al. / Tetrahedron: Asymmetry 11 (2000) 2107±2115
2115
References
1. Ager, D. J.; Prakash, I.; Schaad, D. R. Chem. Rev. 1996, 96, 835±875.
2. Kanerva, L. T. Acta Chem. Scand. 1996, 50, 234±242.
3. Claremon, D. A.; Lumma, P. K.; Phillips, B. T. J. Am. Chem. Soc. 1986, 108, 8265±8266.
4. Mazaki, M.; Morifuji, N.; Takahashi, T.; Hashimoto, K.; Takeda, H. Japanese Patent, Jpn. Kokai Tokkyo Hoho
JP 62209047, 1987; CA 1988, 108, 150043d.
5. Lamant, M.; Guignard, A. Helv. Chim. Acta 1987, 70, 1279±1285.
6. Boerner, A.; Krause, H. Tetrahedron Lett. 1989, 30, 929±930.
7. Kheradmandy, M. Amirkabir 1990, 4, 10; CA 1990, 113, 170361n.
8. E€enberger, F.; Gutterer, B.; Hopf, M.; Hoersch, B.; Ziegler, T. Biochem. Eng.-Stuttgart [Proc. Int. Symp.] 2nd
1990, 130.
9. Jackson, W. R.; Jacobs, H. A.; Jayatilake, G. S.; Matthews, B. R.; Watson, K. G. Aust. J. Chem. 1990, 43, 2045±
2062.
10. Oppolzer, W.; Tamura, O.; Sundarababu, G.; Signer, M. J. Am. Chem. Soc. 1992, 114, 5900±5902.
11. Moran, P. J. S.; Rodrigues, J. A. R.; Joekes, I.; Brenelli, E. C. S.; Leite, R. A. Biocatalysis 1994, 9, 321±328.
12. Kreutz, O. C.; Moran, P. J. S.; Rodrigues, J. A. R. Tetrahedron: Asymmetry 1997, 8, 2649±2653.
13. Slater, W. K. J. Chem. Soc. 1920, 116, 587±591.
14. Buehler, E. J. Org. Chem. 1967, 32, 261±265.
15. Correa Jr., I. R.; Moran, P. J. S. Tetrahedron 1999, 55, 14221±14232.
16. Levy, G. C.; Nelson, G. L. J. Am. Chem. Soc. 1972, 94, 4897±4901.
17. Olivato, P. R.; Ribeiro, D. S.; Rittner, R.; Hase, Y.; del Pra, D.; Bombieri, G. Spectrochim. Acta 1995, 51, 1479±
1495.
18. Nakamura, K.; Kondo, S.; Kawai, Y.; Hida, K.; Kitano, K.; Ohno, A. Tetrahedron: Asymmetry 1996, 7, 409±412.
19. Takeshita, M.; Sato, T. Chem. Pharm. Bull. 1989, 37, 1085±1086.
20. Brenelli, E. C. S.; Moran, P. J. S.; Rodrigues, J. A. R. Synth. Commun. 1990, 20, 261±266.
21. Pines, S. H.; Chemerda, J. M.; Kozlowski, M. A. J. Org. Chem. 1966, 31, 3446±3449.
22. Corey, E. J.; Richman, J. E. J. Am. Chem. Soc. 1970, 92, 5276±5277.
23. Singh, L.; Ram, R. N. Synth. Commun. 1993, 23, 3139±3147.
24. Wali, A.; Ganeshpure, P. A.; Satish, S. Bull. Chem. Soc. Jpn. 1993, 66, 1847±1848.
25. Weigang Jr., O. E. J. Chem. Phys. 1965, 43, 3609±3618.
26. Weigang Jr., O. E.; Ong, E. C. Tetrahedron 1974, 30, 1783±1793.
27. Smith, H. E.; Fontana, L. P. J. Org. Chem. 1991, 56, 432±435.
28. Denmark, S. E.; Dappen, M. S.; Sear, N. L.; Jacobs, R. T. J. Am. Chem. Soc. 1990, 112, 3466±3474.
29. Sorrilha, A. E. P. M.; Marques, M.; Joekes, I.; Moran, P. J. S.; Rodrigues, J. A. R. Bio. Med. Chem. Lett. 1992, 2,
191±196.