Stereoselective chemoenzymatic synthesis of both enantiomers of protected 4-amino-2-pentanone

Article abstract of DOI:10.1016/S0957-4166(99)00234-7

An acetal protected 4-amino-2-pentanone was synthesised by two different routes in 10 and seven steps, respectively, the key step being a microbiological reduction. Both enantiomers of the amine were obtained enantiomerically pure.

Full text of DOI:10.1016/S0957-4166(99)00234-7

Pergamon
Tetrahedron: Asymmetry 10 (1999) 2213–2224
Stereoselective chemoenzymatic synthesis of both enantiomers of
protected 4-amino-2-pentanone
Pascale Besse,a,∗ Stéphane Ciblat,b Jean-Louis Canet,b Yves Troin b and Henri Veschambre a
aLaboratoire de Synthèse, Electrosynthèse et Etude de Systèmes à Intérêt Biologique, UMR 6504 du CNRS,
Université Blaise Pascal, 63177 Aubière Cedex, France
bLaboratoire de Chimie des Hétérocycles et des Glucides, EA 987, Ecole Nationale Supérieure de Chimie de
Clermont-Ferrand, BP 187, 63174 Aubière Cedex, France
Received 16 May 1999; accepted 8 June 1999
Abstract
An acetal protected 4-amino-2-pentanone was synthesised by two different routes in 10 and seven steps,
respectively, the key step being a microbiological reduction. Both enantiomers of the amine were obtained
enantiomerically pure. © 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Previously,1 some of us have reported on a stereoselective synthesis of (2,4)-di- or (2,3,4)-trisubstituted
piperidines, by an intramolecular cyclisation of chiral dienal iron tricarbonyl complexes and an achiral
amine. The stereoselectivity of the reaction arose from the chirality of the organometallic complexes
used and, consequently, chiral organometallic complexes had to be prepared. Another strategy to
affect this cyclisation would consist of starting from a chiral amine and an achiral aldehyde to obtain
substitutions at other positions (see following accompanying paper). For this purpose, enantiomerically
pure substituted primary amines need to be prepared and used as starting materials (Scheme 1).
This fashion of introducing chirality should be attractive since the synthesis of enantiomerically pure
organoiron complexes is not always obvious.
The amine group is one of the fundamental structures in organic chemistry. Chiral amines are
intermediates for many syntheses of drugs or natural products, and are also used as chiral auxiliaries
and resolving agents.2 Several methods have been developed for the preparation of chiral amines. Most
of them correspond to the resolution of racemic amines either by chemical (fractional crystallisation of
the diastereoisomeric salt of the amine with a chiral acid,3 chromatographical (on a chiral stationary
∗
Corresponding author. Fax: 33 4 73 40 77 17; e-mail: besse@chimtp.univ-bpclermont.fr
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00234-7

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Scheme 1. Strategies for the synthesis of chiral substituted piperidines
phase4) or by enzymatic methods (use of lipases,5 enzyme catalysed aminolysis in organic solvents6).
The disadvantage of all these resolution procedures is the theoretical maximum yield limit of 50%. Other
chemical methods, such as nucleophilic 1,2-addition of organometallic reagents7 to imines or reduction
by metal hydrides8 of a CN double bond, or stereoselective Michael addition of a chiral amine to α,β-
unsaturated esters,9 have allowed the synthesis of enantiomerically enriched amines. Those strategies
which use a chiral synthon as starting material are very elegant but the problem can then be, in some
cases, obtaining the enantiomerically pure precursors.
For our own part, we have worked for several years on the microbiological reduction of various keto
compounds10 and have shown that in many cases, by choosing the appropriate microorganism, both
enantiomers of the corresponding alcohol could be obtained with high enantiomeric excesses. So, we
envisaged the preparation of chiral amines through chiral alcohols.
In this paper, the preparation of both enantiomers of protected 4-amino-2-pentanone 1 (Scheme 1,
R0_H, R00_CH3) is reported via a chemoenzymatic synthesis, the key step being a microbiological
reduction of a prochiral keto compound.
2. Results and discussion
2.1. Synthesis of (R)-1 by microbiological reduction of ethyl acetoacetate (Method A)
The first step of our proposed route (Scheme 2) consisted of the microbiological reduction of a β-
ketoester, ethyl acetoacetate 2. For this key step, corresponding to the introduction of the asymmetric
carbon, obtaining the enantiomerically pure hydroxyester is necessary. The asymmetric reduction of
ethyl acetoacetate by baker’s yeast has long been known11 and is now a well-established procedure for
the synthesis of (3S)-ethyl 3-hydroxybutanoate of high but variable enantiomeric excess (ee 77–99%),
according to the method of bioconversion used: fermentation or non-fermentation processes, control of
substrate concentration,12 immobilisation of baker’s yeast,13 or use of specific dehydrogenase inhibitor.14
For our protocol, the following method was chosen: 40 g of freeze-dried baker’s yeast in 500 mL of
distilled water, addition of 1 g of 2, incubation time: 1 h. The (3S)-ethyl 3-hydroxybutanoate 3 was
obtained enantiomerically pure in 70% yield. The enantiomeric excess was determined on the basis of
1
the corresponding MTPA-ester15 by H NMR and showed that 3 was obtained enantiomerically pure.

P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
2215
Since it has been reported by Buisson et al.16 that reduction of 2 by the fungus Geotrichum candidum
yielded (3R)-3 in a 75% yield and with an ee≥98%, both enantiomers of the hydroxyester 3 could be
obtained in an enantiomerically pure form by simply choosing the appropriate microorganism for the
reduction step.
Scheme 2. Synthetic route for the preparation of 1 (Method A). (i) Microbiological reduction with baker’s yeast, (ii)
AcOH/H2O/THF, (iii) PCC
The ester function of the β-hydroxyester was then reduced with LiAlH4 to yield the (+)-(3S)-1,3-
butanediol 4 in 85% yield. At this step, the optical purity of 4 was checked by comparing the value of the
specific rotation of the product obtained with that given in the literature17 ([α]25=+30.3 (c 1.5, MeOH);
D
lit.17 [α]D=+28.9 (c 0.96, MeOH); ee=97%). The primary alcohol function was then selectively and
quantitatively protected as its tert-butyldimethylsilyl derivative 518 and then transformed into phthalimide
6 through a Mitsunobu reaction19 (86% yield). The Mitsunobu reaction is known to take place with an
inversion of configuration, but in some cases, almost complete racemisation has been observed.20 In
order to confirm the stereochemical course of the reaction, we checked the enantiomeric excess and
the absolute configuration of phthalimide 6 (Scheme 3). The first attempts to determine the enantiomeric
excess by classical methods (GC or HPLC fitted out with chiral columns) failed. It was finally determined
by deuterium NMR of its N-trideuteroacetyl derivative in a chiral solvent [dichloromethane solution of
γ-benzyl L-glutamate (PBLG)] as described previously21 and was found to be enantiomerically pure.
Scheme 3.

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P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
The absolute configuration of phthalimide 6 was assigned by chemical correlation (Scheme 3).
After cleavage of the phthalimido group by hydrazinolysis and deprotection of the alcohol function,
3-aminobutanol was obtained. By comparing the sign of the optical rotation of 3-aminobutanol obtained
with that described in the literature,22 the absolute configuration was assigned to be (R). Compound
6 also had the (R) absolute configuration and was obtained enantiomerically pure. So in this case, the
Mitsunobu reaction took place with a complete inversion of configuration.
The alcohol function of 6 was then quantitatively deprotected and oxidised with PCC, yielding the
corresponding aldehyde 8. Homologation of the carbon chain was realised with methylmagnesium
bromide at room temperature. During this reaction, the formation of many by-products was observed,
corresponding in particular to the attack of the alkylmagnesium on the C_O functions of the phthalimide,
a phenomenon that has already been reported (even at 0°C).23 In their case, the best results (in terms
of yield) were obtained at −15°C with 1.1 equiv. of methylmagnesium bromide. A mixture of two
diastereoisomers of 9 was obtained in a 70:30 ratio in an overall yield of 43%. They were not separated
as the next step was the oxidation with PCC of the alcohol function (compound 10). The last two steps
consisted of the protection of the ketone with propane 1,3-diol (yield: 85%) and the deprotection of the
amino function by cleavage of the phthalimido group with hydrazine (yield: 98%). By this route, the
chiral synthon (R)-1 was obtained in 10 steps with a 12% overall yield. The enantiomeric excess of 1
was checked again, even though no reaction had taken place directly on the asymmetric carbon since the
1
Mitsunobu reaction. It was determined by H NMR of 1 in the presence of (+)-mandelic acid as chiral
solvating agent,24 that amine 1 was enantiomerically pure.
2.2. Synthesis of both enantiomers of 1 by microbiological reduction of 4,4-dimethoxy-2-butanone
(Method B)
Another route, containing fewer steps, was then envisaged (Scheme 4), the key step also being a
microbiological reduction. The starting material was 4,4-dimethoxy-2-butanone 12.
Scheme 4. Synthetic route for the preparation of (R)-1 (Method B)
2.2.1. Microbiological reduction of 12
The microbiological reduction of 12 has not been fully studied previously. In the literature, Wong et
al.25 studied the enzymatic reduction of 12 by several alcohol dehydrogenases. In their case, 13 was not

P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
2217
Table 1
Microbiological reductions of 12
characterised and was directly converted into the corresponding MTPA-ester. That is the reason why we
decided to test several strains of microorganisms for the reduction of 12. The results obtained with the
most efficient ones are reported in Table 1.
Most of the microorganisms tested are not able to reduce 12 (data not shown). This compound is
difficult to reduce microbiologically. Even after a long incubation time, the percentage of reduced ketone
was not very high. Only the strains of yeast, and in particular baker’s yeast and Yamadazyma farinosa,
gave enantiomerically pure 13, (S)-13 and (R)-13, respectively, with good yields. In each case, the
enantiomeric excess of the alcohol 13 obtained was determined after conversion into the corresponding
MTPA-ester and analysis by 1H NMR.
2.2.2. Synthesis of both enantiomers of 1
The strategy for the synthesis is similar to that described above: Mitsunobu reaction with both
enantiomers of 13 and deprotection of the aldehyde function yielded 8. For this last step (14 -→ 8),
several reagents were used: wet silica,26 formic acid27 and montmorillonite K10.28 Only the use of
montmorillonite K10 gave 8 in good yield (70%). The value of the specific rotation of 8 obtained by
this method was identical to that obtained by the previous synthesis (Method A). This shorter synthetic
route allowed the preparation of both enantiomers of 1 in enantiomerically pure form, starting from the
alcohol obtained by microbiological reduction either with baker’s yeast ((R)-1) or with Yamadazyma
farinosa ((S)-1). In the case of the reduction with baker’s yeast, (R)-1 was obtained in seven steps with a
13.5% overall yield and an ee≥98%.
The decrease in the number of steps (seven instead of 10) has not, to a great extent, improved the
overall yield. This fact was a little disappointing but not very surprising, since this second synthesis does
not avoid the critical step (in terms of yield) of addition of methylmagnesium bromide on the aldehyde.
A completely different synthetic route of 1, avoiding this limitating step, needs to be envisaged
to improve the overall yield and also to make this route more satisfactory. However, with these two
syntheses, both enantiomers of 1 have been obtained enantiomerically pure. They have been used for the
syntheses of several piperidines (see following paper). Moreover, these methods could be extended to
the synthesis of other chiral amines by simply changing the structure of the alkylmagnesium or of the
starting materials.

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3. Experimental
3.1. General methods
Gas chromatography (GC) was performed using an instrument equipped with a flame ionisation
detector and a 50 m×0.32 mm capillary column coated with Carbowax 20 M. The carrier gas was
hydrogen at 65 kPa. Oven temperature: P1 (40°C for 5 min and then 40 to 200°C at 8°C/min) or P2 (80°C
for 5 min and then 80 to 200°C at 5°C/min). For 1H (400.13 MHz) and 13C (100.61 MHz) NMR spectra,
the chemical shifts were relative to chloroform. Microanalyses were performed by the Service Central
d’Analyses du CNRS, Vernaison (France). High resolution mass spectrometry (HRMS) was performed
by the Centre Régional de Mesures Physiques de l’Ouest, Université de Rennes (France).
3.2. Microbiological methods
The microorganisms were all laboratory-grown except freeze-dried baker’s yeast which was a com-
mercial product (VAHINE, Monteux, France). Preculture, culture and bioconversion conditions for the
fungi Aspergillus niger ATCC 9142 and for the bacterium Lactobacillus kefir DSM 20587 have already
been described elsewhere.29 The yeast Zygosaccharomyces rouxii ATCC 13356 was grown on a medium
containing glucose, 20 g; malt extract, 6 g; yeast extract, 6 g; tryptone (Difco), 10 g and H2O, 1 L;
pH=6.0; preculture and culture: 48 h. The bioconversion was carried out as previously described.29 The
yeast Yamadazyma farinosa IFO 10896 was grown on a medium containing glucose, 50 g; tryptone
(Difco), 7 g; yeast extract, 5 g; K2HPO4, 2 g; KH2PO4, 3 g and H2O, 1 L; pH=6.5; preculture and
culture: 48 h. In this last case, the bioconversion reaction was carried out under anaerobic conditions
according to Ohta.30
3.3. Microbiological reductions
3.3.1. Microbiological reduction of ethyl 3-oxobutanoate 2
In a 1 L Erlenmeyer flask, containing 40 g of baker’s yeast in 500 mL of distilled water, was added,
under stirring, 1 g of ethyl 3-oxobutanoate 2. Incubation time: 1 h. Yield: 70% (700 mg). (+)-(3S)-3:
1H NMR (400.13 MHz) δ: 1.20 (3H, t, J=7.2 Hz), 1.28 (3H, d, J=7.2 Hz), 2.40 (1H, dd, J=8.1 Hz,
J=16.2 Hz), 2.48 (1H, dd, J=4.2 Hz, J=16.4 Hz), 3.15 (1H, s, exchangeable with D2O), 4.19 (3H, m).
[α]25=+39.5 (c 5.4, CHCl3); ee=98%. Lit.31 (+)-(3S)-3: [α]25=+41.5 (c 4.7, CHCl3); ee=98%.
D
D
3.3.2. Determination of the enantiomeric excess of 3
1
The enantiomeric excess was determined by H NMR after converting an aliquot of racemic and
optically active 3 into the corresponding MTPA-ester according to Mosher.15 1H NMR (400.13 MHz)
δ (for the R enantiomer): 1.19 (t, 3H, J=7.2 Hz), 1.42 (d, 3H, J=6.4 Hz), 2.50 (ABX spectrum, dd,
1H, J=4.2 Hz, J=17.5 Hz), 2.70 (ABX spectrum, dd, 1H, J=8.2 Hz, J=17.5 Hz), 3.55 (s, 3H), 4.06 (q,
2H, J=7.2 Hz), 5.50–5.63 (m, 1H), 7.35–7.45 (m, 3H), 7.49–7.56 (m, 2H). For the S enantiomer: 1.24
(t, 3H, J=7.2 Hz), 1.33 (d, 3H, J=6.4 Hz), 2.55 (ABX spectrum, dd, 1H, J=4.2 Hz, J=17.5 Hz), 2.74
(ABX spectrum, dd, 1H, J=8.2 Hz, J=17.5 Hz), 3.55 (s, 3H), 4.12 (q, 2H, J=7.2 Hz), 5.50–5.63 (m, 1H),
7.35–7.45 (m, 3H), 7.49–7.56 (m, 2H).

P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
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3.3.3. Microbiological reductions of 4,4-dimethoxy-2-butanone 12
Incubation times varied and are indicated for each microorganism. The product was purified on a silica
gel column, eluent: pentane:ether, 70:30. In each case, the yields are overall yields after purification.
Baker’s yeast: incubation time: 3 days. The residue from 15 flasks consisted of 23% of 12 and 77%
of (−)-(2S)-13. Yield: 75% (565 mg). (−)-(2S)-13: retention time: 850 s (P1). 1H NMR (400.13 MHz) δ:
1.17 (d, 3H, J=5.2 Hz), 1.65–1.80 (m, 2H), 3.00 (s, 1H, exchangeable with D2O), 3.33 (s, 3H), 3.38 (s,
3H), 3.90–4.00 (m, 1H), 4.55 (t, 1H, J=5.2 Hz). [α]25=−11.7 (c 1.5, CHCl3); ee=98%. Lit.32 (−)-(2S)-13:
D
[α]20=−13.1 (c 1.1, CHCl3); ee=98%.
D
3.3.4. Determination of the enantiomeric excess of 13
1
The enantiomeric excess was determined by H NMR after converting an aliquot of racemic and
optically active 13 into the corresponding MTPA-ester. 1H NMR (400.13 MHz) δ (for the S enantiomer):
1.32 (d, 3H, J=7.2 Hz), 1.80–1.90 (m, 1H), 1.96–2.05 (m, 1H), 3.30 (s, 3H), 3.33 (s, 3H), 3.55 (s, 3H),
4.41 (dd, 1H, J=4.7 Hz, J=7.0 Hz), 5.18–5.30 (m, 1H), 7.37–7.45 (m, 3H), 7.50–7.58 (m, 2H). For the
R enantiomer: 1.38 (d, 3H, J=7.2 Hz), 1.75–1.85 (m, 1H), 1.85–1.95 (m, 1H), 3.25 (s, 3H), 3.28 (s, 3H),
3.58 (s, 3H), 4.21 (dd, 1H, J=4.8 Hz, J=6.9 Hz), 5.18–5.30 (m, 1H), 7.37–7.45 (m, 3H), 7.50–7.58 (m,
2H).
Aspergillus niger: incubation time: 3 days. The residue from five flasks consisted of 77% of 12 and
23% of (−)-(2S)-13. Yield: 20% (50 mg). [α]25=−8.1 (c 2.34, CHCl3); ee=70%.
D
Lactobacillus kefir: incubation time: 4 days. The residue from six flasks consisted of 90% of 12 and
10% of (+)-(2R)-13. Yield: 7% (20 mg). [α]25=+5.1 (c 1.68, CHCl3); ee=45%.
D
Rhodotorula glutinis: incubation time: 3 days. The residue from eight flasks consisted of 70% of 12
and 30% of (−)-(2S)-13. Yield: 26% (105 mg). [α]25=−11.7 (c 2.05, CHCl3); ee=98%.
D
Zygosaccharomyces rouxii: incubation time: 48 h. The residue from six flasks consisted of 80% of 12
and 20% of (−)-(2S)-13. Yield: 18% (58 mg). [α]25=−11.7 (c 0.67, CHCl3); ee=98%.
D
Yamadazyma farinosa: incubation time: 48 h (anaerobic conditions28). The residue from 10 flasks
consisted of 90% of (+)-(2R)-13. Yield: 50% (250 mg). [α]25=+11.7 (c 4.6, CHCl3); ee=98%.
D
3.4. Synthesis of (R)-1 from the (S)-hydroxyester 3 obtained by reduction with baker’s yeast (Method A)
3.4.1. (+)-(3S)-1,3-Butanediol 4
To a suspension of LiAlH4 (1.1 g, 29 mmol) in 30 mL of dry ether was added dropwise a solution
of the (3S)-hydroxyester 3 (5.8 g, 44 mmol) in 20 mL of dry ether. After 6 h of reaction were added
successively 1.1 mL of water, then 1.1 mL of a 30% NaOH solution and finally 2.2 mL of water. The
mixture was filtered on a MgSO4 pad. The filtrate was dried on MgSO4. After evaporation of the solvent,
the residue was purified on a silica gel column, eluent: pentane:ether, 20:80, and then 100% ether. Yield:
85% (3.4 g). Retention time: 840 s (P2). 1H NMR (400.13 MHz) δ: 1.23 (d, 3H, J=7.1 Hz), 1.64–1.74
(m, 2H), 3.45 (s, 2H, exchangeable with D2O), 3.75–3.92 (m, 2H), 4.00–4.11 (m, 1H). [α]25=+30.3 (c
D
1.5, MeOH). Lit.17 (+)-(3S)-4: [α]D=+28.9 (c 0.969, MeOH), ee=97%.
3.4.2. (−)-(3S)-1-(tert-Butyldimethylsilyloxy)-3-butanol 5
To a solution of 4 (1.6 g, 17.8 mmol) and imidazole (3 g, 42.8 mmol) in 30 mL of dry THF, placed in
an ice bath, was added dropwise a solution of 2.70 g (17.8 mmol, 1 equiv.) of TBDMS-Cl in 20 mL of dry
THF. The mixture was stirred for 2 h at room temperature. The solvent was removed under vacuum. The
residue obtained was dissolved in 75 mL of ether and washed three times with water (3×25 mL). The
organic layer was dried on MgSO4. The residue, obtained after evaporation of the solvent, was purified

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P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
by column chromatography, eluent: pentane:ether, 60:40. Yield: 98% (3.5 g). Retention time: 515 s (P2).
1H NMR (400.13 MHz) δ: 0.05 (s, 3H), 0.09 (s, 3H), 0.87 (s, 9H), 1.17 (d, 3H, J=6.1 Hz), 1.54–1.71 (m,
2H), 3.48 (s, 1H, exchangeable with D2O), 3.75–3.82 (m, 1H), 3.83–3.89 (m, 1H), 3.94–4.04 (m, 1H);
13C NMR (100.61 MHz) δ: −5.6 (CH3 TBDMS), −5.5 (CH3 TBDMS), 18.1 (C TBDMS), 23.3 (CH3),
25.9 (3×CH3 TBDMS), 40.1 (CH2), 62.6 (CH2–OTBDMS), 68.1 (CH). HRMS analysis (LSIMS Cs+,
C10H25O2Si=205.1624). Found: 205.1626. [α]25=−2.9 (c 4.43, CHCl3).
D
3.4.3. (−)-(3R)-1-(tert-Butyldimethylsilyloxy)-3-phthalimidobutane 6
To a solution of 5 (2.2 g, 10.8 mmol) in 80 mL of dry THF were added 3.20 g (21.7 mmol) of
phthalimide and 5.70 g (21.7 mmol) of triphenylphosphine. This solution was cooled with an ice bath
and placed under argon. To this mixture was then added dropwise a solution of DEAD (3.8 g, 21.7 mmol)
in 12.5 mL of dry THF. After the end of addition, the mixture was left under stirring overnight at room
temperature. The solvent was then removed under vacuum, and the residue was filtered through a silica
pad (3×5 cm), eluent: hexane:ethyl acetate, 5:1. The filtrate was evaporated and the residue was purified
on a silica gel column, eluent: pentane:ether, 60:40. Yield: 86% (3.1 g). 1H NMR (400.13 MHz) δ: −0.10
(s, 6H), 0.80 (s, 9H), 1.45 (d, 3H, J=6.8 Hz), 1.85–1.98 (m, 1H), 2.23–2.37 (m, 1H), 3.50–3.68 (m,
2H), 4.45–4.60 (m, 1H), 7.62–7.73 (m, 2H), 7.75–7.85 (m, 2H); 13C NMR (100.61 MHz) δ: −5.6 (CH3
TBDMS), −5.5 (CH3 TBDMS), 18.8 (C TBDMS), 18.8 (CH3), 25.8 (3×CH3 TBDMS), 36.3 (CH2), 44.7
(CH), 60.6 (CH2–OTBDMS), 123.0 (Ar), 132.2 (C Ar), 133.7 (Ar), 168.4 (CO). HRMS analysis (LSIMS
Cs+, C18H28NO3Si=334.1838). Found: 334.1834. [α]25=−16.8 (c 4.0, CHCl3).
D
3.4.4. Determination of the enantiomeric excess of 6
The enantiomeric excess was determined by 2H NMR of the derivative obtained by reacting an aliquot
of racemic and optically active 6, after cleavage of the phthalimide function, with acetyl-d3 chloride
(CD3COCl).
3.4.4.1. Cleavage of the phthalimide group. To a solution of 6 (155 mg, 0.46 mmol) in 1.5 mL of
methanol was added 0.5 mL (21.1 equiv., 9.5 mmol) of hydrazine monohydrate. The mixture was refluxed
overnight. After cooling the reaction mixture to room temperature, 1.4 mL of a 2.6N KOH solution was
added. The aqueous layer was extracted three times with dichloromethane (3×5 mL). The combined
organic layers were washed with a saturated brine solution and dried on MgSO4. Yield: 97% (92 mg).
1H NMR (400.13 MHz) δ: 0.05 (s, 6H), 0.90 (s, 9H), 1.10 (d, 3H, J=7.1 Hz), 1.45–1.60 (m, 2H), 2.02
(s, 2H, exchangeable with D2O), 3.00–3.15 (m, 1H), 3.60–3.77 (m, 2H); 13C NMR (100.61 MHz) δ:
−5.6 (CH3 TBDMS), −5.5 (CH3 TBDMS), 18.3 (C TBDMS), 19.9 (CH3), 26.0 (3×CH3 TBDMS), 38.2
(CH2), 45.8 (CH), 60.4 (CH2–O).
3.4.4.2. Synthesis of the deuterated derivative. To a solution of amine (0.45 mmol, 92 mg) and dry
triethylamine (1.2 equiv., 0.54 mmol, 55 mg, 75.5 µL) in 5 mL of dry ether, under argon and cooled at
0°C, was added acetyl-d3 chloride (1.1 equiv., 0.50 mmol, 35.5 µL). The reaction mixture was stirred for
10 min at 0°C, and then 15 min at room temperature. A white precipitate (triethylamine hydrochloride)
appeared. After filtration of this precipitate and evaporation of the solvent, the residue was purified by
1
column chromatography, eluent: pentane:ether, 80:20, and then 100% ether. Yield: 57% (64 mg). H
NMR (400.13 MHz) δ: 0.05 (s, 3H), 0.09 (s, 3H), 0.90 (s, 9H), 1.15 (d, 3H, J=6.9 Hz), 1.50–1.62
(m, 1H), 1.68–1.83 (m, 1H), 3.61–3.72 (m, 1H), 3.72–3.85 (m, 1H), 3.98–4.15 (m, 1H), 6.45 (s, 1H,

P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
2221
exchangeable with D2O). [α]25=−11.7 (c 0.6, CHCl3); ee=98%; 2H NMR (303 K): racemic: ∆ν1=148.5
D
Hz, ∆ν2=108.2 Hz, (3R)-deuterated compound: ∆ν=150.0 Hz.
3.4.5. Determination of the absolute configuration of 6
3.4.5.1. Cleavage of the phthalimide function of 6. The same procedure as that described above was
used. Yield: 97%.
3.4.5.2. Synthesis of (3R)-3-aminobutanol. To a solution of 1-(tert-butyldimethylsilyloxy)-3-
aminobutane (100 mg, 0.49 mmol) in 3 mL of dry THF was added, under stirring, 4.5 mL of a 1 M
solution of tetrabutylammonium fluoride in THF. The mixture was stirred for 1 h. Then an aqueous
solution of ammonium chloride was added and the reaction mixture was extracted four times with ether.
The organic layer was dried on MgSO4. After evaporation of the solvent, the residue was purified on
1
a silica gel column, eluent: ethyl acetate:MeOH, 70:30. Yield: 80% (35 mg). H NMR (400.13 MHz)
δ: 1.28 (d, 3H, J=6.6 Hz), 1.52–2.00 (m, 2H), 3.30–3.50 (m, 1H), 3.53–3.86 (m, 2H), 5.50 (s, 3H,
exchangeable with D2O). [α]25=−25.0 (c 1.25, EtOH). Lit.22: (+)-(3S)-3-aminobutanol: [α]20=+16.3 (c
D
D
4.5, EtOH).
3.4.6. (−)-(3R)-3-Phthalimido-1-butanol 7
A solution of 6 (2.2 g, 6.6 mmol) in a mixture of glacial acetic acid:water:THF, 3:1:1 (21.6 mL) was
stirred overnight at room temperature. The mixture was concentrated under vacuum and the water and
acetic acid traces were removed by co-distillation with toluene (2×20 mL) under reduced pressure. The
white solid obtained was purified by column chromatography, eluent: pentane:ether, 50:50. Yield: 98%
(1.4 g); mp=65–66°C. 1H NMR (400.13 MHz) δ: 1.47 (d, 3H, J=7.0 Hz), 1.92–2.06 (m, 1H), 2.20–2.30
(m, 1H), 2.52 (s, 1H, exchangeable with D2O), 3.50–3.57 (m, 1H), 3.61–3.68 (m, 1H), 4.51–4.62 (m,
1H), 7.62–7.70 (m, 2H), 7.72–7.80 (m, 2H); 13C NMR (100.61 MHz) δ: 18.5 (CH3), 36.3 (CH2), 44.2
(CH), 59.5 (CH2OH), 123.0 (Ar), 131.8 (C Ar), 133.9 (Ar), 168.7 (CO). Anal. calcd for C12H13NO3: C,
65.75; H, 5.94; N, 6.39. Found: C, 65.69; H, 6.01; N, 6.37. [α]25=−26.6 (c 13.3, CHCl3).
D
3.4.7. (−)-(3R)-3-Phthalimidobutanal 8
To a suspension of 1.8 g (1.5 equiv., 8.25 mmol) of PCC in methylene chloride was added rapidly
a solution of 7 (1.2 g, 5.5 mmol) in 12 mL of methylene chloride. The mixture was stirred for 3 h at
room temperature. The black reaction mixture was diluted with 5 vol. of anhydrous ether, the solvent
was decanted, and the black solid was washed twice with ether (causing it to be granular). Product was
isolated simply by filtration of the organic extracts through Florisil and evaporation of the solvent at
reduced pressure. The residue was then purified by column chromatography on silica gel, eluent: ethyl
acetate:cyclohexane, 40:60. A white solid was isolated with an 82% yield (975 mg); mp=105–106°C. 1H
NMR (400.13 MHz) δ: 1.47 (d, 3H, J=6.9 Hz), 3.00 (ddd, 1H, J=1.0 Hz, J=5.9 Hz, J=17.2 Hz), 3.29
(ddd, 1H, J=1.0 Hz, J=8.4 Hz, J=17.2 Hz), 4.89 (m, 1H), 7.65–7.75 (m, 2H), 7.75–7.85 (m, 2H), 9.80
(s, 1H); 13C NMR (100.61 MHz) δ: 18.8 (CH3), 41.4 (CH2), 47.3 (CH), 123.2 (Ar), 131.8 (C Ar), 134.0
(Ar), 168.1 (CO), 199.4 (CHO). Anal. calcd for C12H11NO3: C, 66.36; H, 5.07; N, 6.45. Found: C, 66.34;
H, 5.18; N, 6.37. [α]25=−3.6 (c 2.3, CHCl3).
D
3.4.8. (2R,4R)- and (2S,4R)-4-Phthalimido-2-pentanol 9
In a round-bottom flask was stirred, under argon, 0.92 g (4.24 mmol) of 8 in 40 mL of dry THF.
To this mixture cooled at −15°C, was added dropwise 1.55 mL (1.1 equiv.) of a 3 M solution of

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P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
methylmagnesium bromide in THF. The reaction mixture was stirred at −10°C for 5 h, and then
hydrolysed by a mixture of water and THF. The aqueous layer was washed three times with ether. The
combined organic layers were evaporated, and the residue was purified on a silica gel column, eluent:
pentane:ether, 40:60. A mixture of both diastereoisomers (ratio: 70:30) was obtained. Yield: 43% (425
1
mg). H NMR (400.13 MHz) δ: 1.10, 1.16 (d, 3H, J=6.3 Hz), 1.42, 1.46 (d, 3H, J=7.0 Hz), 1.56–1.66,
1.80–1.89 (m, 1H), 2.06–2.16, 2.15–2.24 (m, 1H), 2.36 (s, 1H, exchangeable with D2O), 3.55–3.65,
3.75–3.90 (m, 1H), 4.48 (m, 1H), 4.51–4.60 (m, 1H), 7.65–7.75 (m, 2H), 7.75–7.85 (m, 2H); 13C NMR
(100.61 MHz) δ: 18.7, 18.8 (CH3); 23.1, 24.1 (CH3); 42.6, 43.1 (CH2); 44.3, 45.0 (CH–N); 64.6, 66.2
(CH–O), 123.0, 123.2 (Ar), 131.8, 132.0 (C Ar), 133.7, 134.0 (Ar), 168.7, 168.9 (CO).
3.4.9. (−)-(4R)-4-Phthalimido-2-pentanone 10
To a suspension of 1.4 g (1.5 equiv., 6.45 mmol) of PCC in 60 mL of methylene chloride was added
rapidly a solution of 9 (1 g, 4.25 mmol) in 20 mL of methylene chloride. The mixture was stirred for 3
h at room temperature. The black reaction mixture was diluted with 5 volumes of anhydrous ether, the
solvent was decanted, and the black solid was washed twice with ether (causing it to be granular). Product
was isolated simply by filtration of the organic extracts through Florisil and evaporation of the solvent
at reduced pressure. The residue was then purified by column chromatography on silica gel, eluent:
pentane:ether, 50:50. A white solid was isolated with an 85% yield (845 mg); mp=60–62°C. 1H NMR
(400.13 MHz) δ: 1.42 (d, 3H, J=6.9 Hz), 2.13 (s, 3H), 3.00 (ABX spectrum, dd, 1H, J=6.4 Hz, J=17.8
Hz), 3.29 (ABX spectrum, dd, 1H, J=8.0 Hz, J=17.8 Hz), 4.82 (m, 1H), 7.65–7.71 (m, 2H), 7.76–7.82
(m, 2H); 13C NMR (100.61 MHz) δ: 18.8 (CH3), 30.1 (CH3), 42.4 (CH–N), 46.9 (CH2), 123.1 (Ar),
131.9 (C Ar), 133.9 (Ar), 168.2 (CO phthalimide), 205.8 (CO). Anal. calcd for C13H13NO3: C, 67.53; H,
5.63; N, 6.06. Found: C, 67.52; H, 5.73; N, 6.13. [α]25=−2.2 (c 8.65, CHCl3).
D
3.4.10. (−)-(2R)-1-(2-methyl-1,3-dioxan-2-yl)-2-phthalimidopropane 11
In a round bottomed flask, fitted with a Dean–Stark apparatus, was added, to a solution of 10 (0.87
g, 3.8 mmol) in 12 mL of toluene, 545 µL of freshly distilled propane-1,3-diol (2 equiv., 7.6 mmol,
535 mg) and 20 mg of APTS. The mixture was refluxed for 5 h, then cooled to room temperature and
treated with a saturated NaHCO3 solution. The two layers were separated, and the aqueous one was
extracted several times with dichloromethane. The combined organic layers were washed with a brine
solution and then dried on MgSO4. After evaporation of the solvent, the residue was purified by silica
gel chromatography, eluent: pentane:ether, 60:40. Yield: 85% (925 mg); mp=78–79°C. 1H NMR (400.13
MHz) δ: 1.23–1.34 (m, 1H), 1.36 (s, 3H), 1.47 (d, 3H, J=6.9 Hz), 1.65–1.80 (m, 1H), 1.80 (dd, 1H, J=3.0
Hz, J=15.4 Hz), 2.74 (dd, 1H, J=10.2 Hz, J=15.4 Hz), 3.40–3.50 (m, 1H), 3.69–3.86 (m, 3H), 4.73–4.85
(m, 1H), 7.61–7.71 (m, 2H), 7.75–7.85 (m, 2H); 13C NMR (100.61 MHz) δ: 19.9 (CH3), 20.0 (CH3),
25.0 (CH2 acetal), 42.2 (CH–N), 42.5 (CH2), 59.7, 59.8 (CH2 acetal), 98.4 (C acetal), 122.9 (Ar), 132.3
(C Ar), 133.5 (Ar), 168.7 (CO phthalimide). Anal. calcd for C16H19NO4: C, 66.43; H, 6.57; N, 4.84.
Found: C, 66.39; H, 6.67; N, 4.91. [α]25=−2.2 (c 8.65, CHCl3).
D
3.4.11. (−)-(2R)-1-(2-Methyl-1,3-dioxan-2-yl)-2-aminopropane 1
To a solution of 11 (0.7 g, 2.42 mmol) in 7 mL of methanol was added 2.7 mL (21.1 equiv., 0.05 mol)
of hydrazine monohydrate. The mixture was refluxed overnight. After cooling the reaction mixture to
room temperature, 11 mL of a 2.6N KOH solution was added. The aqueous layer was extracted three
times with dichloromethane (3×10 mL). The combined organic layers were washed with a saturated
brine solution and dried on MgSO4. After evaporation of the solvent under reduced pressure (without
1
heating), a yellow oil of 1 was obtained in a 97% yield (375 mg). H NMR (400.13 MHz) δ: 0.96 (d,

P. Besse et al. / Tetrahedron: Asymmetry 10 (1999) 2213–2224
2223
3H, J=6.5 Hz), 1.26 (s, 3H), 1.30–1.38 (m, 1H), 1.40–1.50 (m, 1H), 1.60–1.80 (m, 2H), 3.10 (s, 2H,
exchangeable with D2O), 3.19–3.30 (m, 1H), 3.65–3.75 (m, 2H), 3.75–3.85 (m, 2H); 13C NMR (100.61
MHz) δ: 19.9 (CH3), 23.6 (CH3), 25.2 (CH2 acetal), 42.7 (CH2), 47.8 (CH–N), 59.3, 59.5 (CH2 acetal),
98.9 (C acetal). Anal. calcd for C8H17NO2: C, 60.35; H, 10.76; N, 8.80. Found: C, 60.39; H, 10.69; N,
8.77. [α]25=−17.5 (c 2.03, CHCl3).
D
3.4.12. Determination of the enantiomeric excess of 1
In an NMR tube was placed 9.6 mg of (+)-mandelic acid. To this solid was added a solution of racemic,
or optically pure 1 (10 mg, 1 equiv.) in CDCl3. The mixture was stirred vigorously and the NMR spectrum
1
was recorded. H NMR (400.13 MHz) δ: Racemic 1: 3.43 (m, 1H), 3.53 (m, 1H); (R)-1: 3.53 (m, 1H);
ee=98%.
3.5. Synthesis of (R)-1 from (S)-4,4-dimethoxy-2-butanol obtained by reduction with baker’s yeast
(Method B)
3.5.1. (−)-(3R)-4,4-Dimethoxy-3-phthalimidobutane 14
To a solution of 13 (0.32 g, 2.4 mmol) in 18 mL of dry THF was added 0.70 g (4.8 mmol) of
phthalimide and 1.30 g (4.8 mmol) of triphenylphosphine. This solution was cooled with an ice bath and
placed under argon. To this mixture was then added dropwise a solution of DEAD (0.85 g, 4.8 mmol)
in 2.5 mL of dry THF. Same work-up as that described previously for 6. The residue was purified on a
1
silica gel column, eluent: pentane:ether, 60:40. Yield: 80% (502 mg). H NMR (400.13 MHz) δ: 1.46
(d, 3H, J=7.0 Hz), 1.85–2.00 (m, 1H), 2.35–2.50 (m, 1H), 3.15 (s, 3H), 3.25 (s, 3H), 4.32 (t, 1H, J=7.0
Hz), 4.43–4.55 (m, 1H), 7.61–7.71 (m, 2H), 7.75–7.85 (m, 2H); 13C NMR (100.61 MHz) δ: 18.9 (CH3),
36.1 (CH–N), 43.7 (CH2), 52.7, 52.8 (OCH3), 102.5 (CH), 122.9 (Ar), 131.9 (C Ar), 133.7 (Ar), 168.3
(CO phthalimide). HRMS analysis (LSIMS Cs+, C14H16NO4=262.1079). Found 262.1079. [α]25=−5.5
D
(c 10.85, CHCl3).
3.5.2. (−)-(3R)-3-Phthalimidobutanal 8
Compound 14 (0.85 g, 3.25 mmol) was dissolved in 100 mL of dichloromethane and montmorillionite
K10 (800 mg) was added. The mixture was stirred for 1 h at room temperature. Once the starting material
has been consumed, the yellow solution was filtered through Celite to remove the K10. The Celite was
washed with dichloromethane (3×30 mL) and the solvent removed under reduced pressure to give a
white solid. Purification by column chromatography (eluent: ethyl acetate:cyclohexane, 20:80) gave 8
with a 70% yield (490 mg). Same NMR spectra and melting point as those described above. [α]25=−3.5
D
(c 2.20, CHCl3).
3.6. Synthesis of (S)-1 from (2R)-4,4-dimethoxy-2-butanol obtained with Y. farinosa (Method B)
The same methods were used as those described above, starting from (2R)-13 obtained by microbiolo-
gical reduction with Y. farinosa. (S)-1 was then obtained. [α]25=+17.5 (c 2.45, CHCl3).
D
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