Chemoenzymatic preparation of optically active secondary amines: a new efficient route to enantiomerically pure indolines

Article abstract of DOI:10.1016/j.tetasy.2006.08.012

An efficient chemoenzymatic route for the synthesis of optically active substituted indolines has been developed. Different lipases have been tested in the alkoxycarbonylation of these secondary amines, Candida antarctica lipase A (CAL-A) was found to be the best biocatalyst for 2-substituted-indolines, and C. antarctica lipase B (CAL-B) for 3-methylindoline. The combination of lipases with a variety of allyl carbonates and tert-butyl methyl ether (TBME) as solvent has allowed the isolation of the carbamate and amine derivatives with a high level of enantiopurity.

Full text of DOI:10.1016/j.tetasy.2006.08.012

Tetrahedron: Asymmetry 17 (2006) 2558–2564
Chemoenzymatic preparation of optically active secondary amines:
a new efficient route to enantiomerically pure indolines
*
´
´
Vicente Gotor-Fernandez, Pedro Fernandez-Torres and Vicente Gotor
Departamento de Quı´mica Orga´nica e Inorga´nica, Instituto Universitario de Biotecnologı´a de Asturias,
Universidad de Oviedo, 33071 Oviedo (Asturias), Spain
Received 18 August 2006; accepted 21 August 2006
Available online 22 September 2006
Abstract—An efficient chemoenzymatic route for the synthesis of optically active substituted indolines has been developed. Different lip-
ases have been tested in the alkoxycarbonylation of these secondary amines, Candida antarctica lipase A (CAL-A) was found to be the
best biocatalyst for 2-substituted-indolines, and C. antarctica lipase B (CAL-B) for 3-methylindoline. The combination of lipases with a
variety of allyl carbonates and tert-butyl methyl ether (TBME) as solvent has allowed the isolation of the carbamate and amine deriv-
atives with a high level of enantiopurity.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
The indole and indoline cores have attracted particular
attention in recent years due to their presence in a great
variety of natural products, biologically active alkaloids
and pharmaceuticals.15 Unfortunately, the enzymatic reso-
lution of optically active indolines has been limited to a
couple of examples in which good enantiomeric excesses
are obtained, but low conversions were achieved using sub-
tilisin as the biocatalyst.14b,d
Optically active secondary amines are important chiral
building blocks in the preparation of pharmaceuticals
and agrochemicals.1 In addition, they possess important
applications in organic asymmetric synthesis as chiral aux-
iliaries,2 catalysts3 or resolving agents.4 For that reason,
many chemical processes have been reported for the prep-
aration of this class of compounds using chiral auxiliaries,5
asymmetric hydrogenation,6 reductive amination7 or
hydrosilylation conditions,8 with the recrystallization of
diastereomeric salts being the most common methodology
for the isolation of the amines.9 On the other hand,
enzyme-catalyzed processes have recently shown their
potential in the preparation of enantioenriched secondary
amines using aminoacylases,10 proteases11 or amino
oxidases obtained by directed evolution methods.12
Herein, we report the development of a practical chemo-
enzymatic route for the preparation of optically active
2- or 3-substituted-indolines through enzymatic alkoxycarb-
onylation procedures. An extensive optimization study of
the reaction parameters in terms of biocatalyst and solvent
was carried out for the isolation of enantiomerically pure
compounds.
Lipases usually accept a wide range of racemic substrates in
order to catalyze their transformation into enantiomeri-
cally pure compound.13 However until now, only a few
examples of the lipase-catalyzed enzymatic kinetic resolu-
tion of secondary amines have been published in the
literature.14
2. Results and discussion
Initially the resolution by acetylation procedures of com-
mercially available 2-methylindoline 1 was carried out
using different lipases such as CAL-A, CAL-B and Candida
rugosa lipase (CRL) with toluene as a solvent and ethyl
acetate (EtOAc) as the acyl donor, achieving only low con-
versions in the case of CAL-B, but promising enantioselec-
tivities. The use of different solvents, acyl donor and high
temperatures did not allow the formation of the corre-
sponding amides in appreciable yields, so at this point we
*
Corresponding author. Tel./fax: +34 985 103448; e-mail: vgs@fq.
uniovi.es
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.08.012

V. Gotor-Ferna´ndez et al. / Tetrahedron: Asymmetry 17 (2006) 2558–2564
2559
turned our attention to the study of the alkoxycarbonyl-
ation reaction of 1, a process that has shown excellent
results for the enzymatic resolution of 1-methyl-1,2,3,4-
tetrahydroisoquinoline.14g
These initial encouraging results, in terms of enantioselec-
tivity, made us focus our attention onto the search for ade-
quate alkoxycarbonylating reagents, which would permit
us to increase the reaction conversion up to values around
50%. To this end, we synthesized three different carbonates
2b–d following the procedures described by Breen,14g to
compare their reactivity in the kinetic resolution of ( )-1
using the best conditions found in previous attempts for
its enzymatic resolution; TBME as a solvent, a ratio of
amine versus carbonate of 1:5, a temperature of 45 ꢁC
and CAL-A as biocatalyst. However, in these cases we em-
ployed double the amount of enzyme in order to reach
higher conversions (Scheme 2).
Diallyl carbonate was selected as the alkoxycarbonylating
reagent for an initial screening of enzyme activity using
dry Et2O as a solvent (Scheme 1, Table 1). In this way at
30 ꢁC, CAL-B and CRL did not show any activity (entries
1 and 2), while CAL-A showed a low reaction rate, but dis-
played complete enantioselectivity, affording 13% of the
carbamate (+)-3 (entry 3). This is not a surprising result
as CAL-A has been identified as an ideal catalyst in the res-
olution of sterically hindered compounds.16 Pseudomonas
cepacia lipase (PSL-C) was also attempted but low conver-
sions were observed (entry 4), so we decided to study the
behaviour of other non-polar solvents such as toluene
and tert-butyl methyl ether (TBME, entries 5 and 6) finding
TBME to be a good candidate for the enzymatic resolution
of ( )-1, partly because slightly higher conversions were
achieved than is the case with Et2O, and partly because
its higher boiling point allows the possibility of increasing
the temperature of the process. As shown in Table 1,
CAL-A reached higher conversions (20–25%) at 45 ꢁC
whilst maintaining a complete enantiopreference for the
(+)-enantiomer (entries 7 and 8). By comparison of the spe-
cific rotation previously described in the literature with the
one obtained in the enzymatic resolution process {experi-
N
O
O
CAL-A
(
R)-3
+
+
O
N
H
TBME
RO
O
45 °C, 250 rpm
( )-1
2a-d
2a: R = allyl
N
methoxyphenyl
2c: R = phenyl
2b: R = 3-
H
(S
)-1
2d
: R = 2-methylphenyl
Scheme 2. Enzymatic kinetic resolution of ( )-1 using different allyl
carbonates.
Observing the results shown in Table 2, these mixed car-
bonates presented higher activities than the diallyl carbon-
ate, and except for the phenyl carbonate 2c, all of them
afforded the enantiomerically pure amide (+)-3. It is of
note that conversions close to 50% were reached using both
carbonates 2b and 2d. However, the latter presented serious
problems in the isolation of reaction products, so we
decided to perform the optimization of the enzymatic reso-
lution of ( )-1 using the 3-methoxyphenyl allyl carbonate
2b (Scheme 3).
20
20
mental ½aꢀD ¼ ꢁ16:3 (c 0.5, CHCl3), literature ½aꢀD
¼
ꢁ12:2 (c 2.6, benzene)}, the absolute configuration of the
recovered amine was assigned as (S),5c and the (R)-carba-
mate being obtained.14b,d
N
O
(R)-3
O
Enzyme
O
+
+
N
H
Table 2. Enzymatic kinetic resolution of ( )-1 with different carbonates in
a ratio of 1:5 and CAL-A with a proportion of 2:1 in weight with respect
to the amine in TBME at 45 ꢁC
Solvent
O
O
2a
T, 250 rpm
( )-1
N
H
eeS (%)a
eeP (%)a
c (%)b
Ec
(S
)-1
Entry
2
t (h)
1
2
3
4
2a
2b
2c
2d
111
67
66
33
87
83
94
>99
>99
82
25
47
50
49
>200
>200
27
Scheme 1. Enzymatic kinetic resolution of 2-methylindoline employing
diallyl carbonate.
67
>99
>200
a Calculated by HPLC.
b c = eeS/(eeS + eeP).
Table 1. Enzymatic kinetic resolution of 2-methylindoline using diallyl
carbonate
c E = ln[(1 ꢁ c) · (1 ꢁ eeS)]/ln[(1 ꢁ c) · (1 + eeS)].
Entry Enzyme Solvent
T
Ratioa
t
eeS eeP
c
Ed
(ꢁC)
(h) (%)b (%)b (%)c
1
2
3
4
5
6
7
8
CAL-B Et2O
CRL Et2O
CAL-A Et2O
PSL-C Et2O
CAL-A Toluene 60 1:5
CAL-A TBME 30 1:5
CAL-A TBME 45 1:5
CAL-A TBME 45 1:10
30 1:5
30 1:5
30 1:5
30 1:5
88 —
88 —
136 15
88 —
—
—
>99 13
18
>99 12
>99 15
>99 20
>99 25
—
—
—
—
>200
N
O
5
1.5
(R)-3
OMe
O
87 14
>200
>200
>200
>200
CAL-A
+
O
+
135 18
135 25
111 33
N
H
TBME
O
O
45 °C, 250 rpm
( )-1
2b
N
a The ratio of amine/diallyl carbonate.
b Calculated by HPLC.
H
(S)-1
c c = eeS/(eeS + eeP).
Scheme 3. Enzymatic kinetic resolution of 2-methylindoline using
d E = ln[(1 ꢁ c) · (1 ꢁ eeS)]/ln[(1 ꢁ c) · (1 + eeS)].
3-methoxyphenyl allyl carbonate.

2560
V. Gotor-Ferna´ndez et al. / Tetrahedron: Asymmetry 17 (2006) 2558–2564
Kinetic resolution of racemic 2-methylindoline was then at-
tempted by varying the different reaction conditions such
as the amount of biocatalyst, solvent, temperature and
the amount of carbonate (Table 3). Firstly the amount of
carbonate was reduced in order to both avoid any possible
formation of by-products, and reduce inhibition effects at
high concentrations of the reactants. However, with only
1 equiv of carbonate, the reaction stopped at 34% conver-
sion (entry 2). Increasing the amount of 2b to 2–2.5 equiv,
conversions of around 50% are obtained with excellent
enantioselectivities (entries 3 and 4). In order to design
an economic process, we decided to study the recycling of
the enzyme, observing non-appreciable loss of activity after
two cycles (entries 5 and 6), and a slower reaction rate in
the third cycle in spite of the excellent enantioselectivity
obtained (entry 7).
Once we had satisfactorily developed an enzymatic proce-
dure for the resolution of an indoline derivative, we
decided to extend this methodology to the chemoenzymatic
synthesis of different indolines using the corresponding
indoles as starting materials. These can be transformed in
the chiral cyclic secondary amines with very good yields
by reduction with sodium cyanoborohydride (NaBH3CN)
in acetic acid following a modified protocol of the type
described by Gribble and Hoffman (Scheme 4).17
Table 3. Enzymatic kinetic resolution of 2-methylindoline using 2b and
CAL-A with a ratio of 2:1 in weight with respect to the amine in TBME
at 45 ꢁC
Entry
Ratioa
t (h)
eeS (%)b
eeP (%)b
c (%)c
Ed
1
2
3
4
5f
6g
7h
1:5
1:1
1:2
1:2.5
1:2.5
1:2.5
1:2.5
67
63
69
66
66
66
66
87
51
90
>99 (88)e
97
88
73
>99
>99
98
47
34
48
50
50
47
43
>200
>200
>200
>200
>200
>200
>200
>99 (90)e
97
Under the same conditions as those used for the kinetic res-
olution of ( )-1, the 2-substituted-indoline with a phenyl
group at the C-2-position instead of a methyl group (entry
1, Table 4), or indolines with different groups at the C-5-
position (entries 2 and 3) were used, observing a complete
enantiopreference in lower reaction times. It is worthy of
note that the isolation of the products in the enzymatic
resolution of 1 and 5a required only a flash chromatogra-
phy purification step to obtain the corresponding optically
active amines and carbamates in high levels of purity.
However, the fact that the Rf values of the remaining
99
>99
a The ratio of amine/carbonate in mmol.
b Calculated by HPLC.
c c = eeS/(eeS + eeP).
d E = ln[(1 ꢁ c) · (1 ꢁ eeS)]/ln[(1 ꢁ c) · (1 + eeS)].
e Isolated yields in brackets.
f Enzyme recovered from entry 4.
g Enzyme recovered from entry 5.
h Enzyme recovered from entry 6.
R2
R3
R2
R2
R2
2b
R1
O
*
R3
R3
R3
*
NaBH3CN
AcOH, rt
Enzyme
N
R1
*
R1
R1
+
*
TBME
N
N
N
O
H
H
H
T, 250 rpm
4a-d
(
R
)-6a-c
)-6d
(
S
)-5a-c
4a R1=Ph, R2=H, R3=H
4b R1=Me, R2=H, R3=OMe
4c R1=Me, R2=H, R3=F
4d R1=H, R2=Me, R3=H
5a-d
(
S
(R)-5d
Scheme 4. Enzymatic kinetic resolution of different indolines using 3-methoxyphenyl allyl carbonate.
Table 4. Enzymatic kinetic resolution of 2-methylindoline using 3-methoxyphenyl allyl carbonate
Entry
Enzyme
Carbonate
R1
R2
R3
T (ꢁC)
Ratioa
t (h)
eeS (%)b
eeP (%)b
c (%)c
Ed
1
2
3
4
5
6
7
8
9
CAL-Ae
CAL-Ae
CAL-Ae
CAL-Ae
CAL-Ae
CAL-Be
CAL-Be
CAL-Bf
CAL-Bf
2b
2b
2b
2b
2b
2b
2b
2b
2a
Ph
Me
Me
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
H
OMe
F
H
H
H
H
H
H
45
45
45
45
30
45
30
30
30
1:2.5
1:2.5
1:2.5
1:2.5
1:1
1:2.5
1:2.5
1:2.5
1:2.5
20
20
20
4
15
16
21
9
97 (78)
>99 (82)
>99 (76)
>99
90
>99
>99
>99
>99 (88)
>99 (90)
95g (84)
>99 (81)
23
39
73
77
93
97 (92)
50
51g
50
81
70
58
56
52
51
>200
>200
>200
6
6
32
39
145
>200
10
a The ratio of amine/carbonate in mmol.
b Calculated by HPLC.
c c = eeS/(eeS + eeP).
d E = ln[(1 ꢁ c) · (1 ꢁ eeS)]/ln[(1 ꢁ c) · (1 + eeS)].
e Using a ratio of amine/enzyme (1:2) in weight.
f Using a ratio of amine/enzyme (1:1) in weight.
g Conversion calculated by 1H NMR of the crude and the eeS from eeP = eeS · (1 ꢁ 1/c).

V. Gotor-Ferna´ndez et al. / Tetrahedron: Asymmetry 17 (2006) 2558–2564
2561
amines 5b and 5c were very similar to that of 3-methoxy-
phenol, by-product obtained in the enzymatic reactions
caused us to develop a different purification procedure
for these substrates, which included an additional extrac-
tion separation step (see Section 4).
ing the conditions depending on the specific substrate.
Melting points were taken on samples in open capillary
tubes and are uncorrected. IR spectra were recorded using
NaCl plates or KBr pellets in a Perkin–Elmer 1720-X F7.
1
1H, 13C NMR, DEPT, H–1H homonuclear experiments
and 1H–13C heteronuclear experiments were obtained using
AC-200 (1H, 200.13 MHz and 13C, 50.3 MHz), AC-300
(1H, 300.13 MHz and 13C, 75.5 MHz), DPX 300 (1H,
300.13 MHz and 13C, 75.5 MHz), AV-400 (1H,
400.13 MHz and 13C, 100.6 MHz) or AV-600 (1H,
600.15 MHz and 13C, 150.9 MHz) spectrometers. Chemical
shifts are given in delta (d) values and the coupling con-
stants (J) in Hertz (Hz). ESI+ using a HP1100 chromato-
graph mass detector, or EI with a Finigan MAT 95
spectrometer were used to record mass spectra (MS).
Microanalyses were performed on a Perkin–Elmer model
2400 instrument. Measurement of the optical rotation
was done in a Perkin–Elmer 241 polarimeter.
A different behaviour was observed for 3-methylindoline
5d; the amine reacted very quickly and with a poor enantio-
selectivity value (entry 4). Attempts to perform the reaction
under milder conditions with respect to temperature and a
smaller amount of carbonate did not result in better selec-
tivities, so we decided to study the influence of a different
enzyme such as CAL-B (entries 6–8). This showed a lower
reaction rate and a very good selectivity, especially at 30 ꢁC
and using a smaller ratio of biocatalyst. Due to the good
selectivity presented by CAL-B and the low reactivity of
the diallyl carbonate, the kinetic resolution of racemic 5d
was attempted at 30 ꢁC in TBME, using 2.5 equiv of 2a
and CAL-B in a ratio of 1:1 in weight with respect to the
amine. After 10 h, a conversion of 51% was reached, the
amine was enantiomerically pure and the corresponding
carbamate was isolated in 97% ee (entry 9). By comparison
with the data described in the literature, the amine was
assigned an (R)-configurations and so the amide resulted
with (S)-configuration6d (Table 4).
4.2. Typical experimental procedure for the reduction of
indoles 4a–d to indoline derivatives 5a–d
To a solution of the corresponding indole 5a–d (1.86 mmol)
in AcOH (9.3 mL) was added NaBH3CN (11.16 mmol),
and the resulting mixture stirred until no starting material
could be detected by TLC analysis (2–8 h). Then, 25 mL
of H2O and additional NaOH pellets were added until
pH >12, extracting the solution with Et2O (3 · 25 mL).
The organic phases were combined, dried over Na2SO4
and the solvent was evaporated under reduced pressure,
to give a crude that was purified by flash chromatography.
3. Conclusions
In conclusion, we have developed an efficient chemoenzy-
matic route for the production of enantiomerically pure
indolines, with CAL-A proving as an excellent enzyme
for the kinetic resolution of 2-substituted-indolines, while
CAL-B showed greater effectivity in the kinetic resolution
of 3-methylindoline. Different parameters have been stud-
ied such as the alkoxycarbonylating agent, temperature,
solvent and the amount of enzyme, amine and carbonate,
in order to establish the optimal reaction conditions for
the development of successful enzymatic resolutions for
this type of secondary cyclic amines. In addition, the recy-
cling of CAL-A in the kinetic resolution of 2-methyl-indo-
line has been studied, with no significant loss of activity
observed after two cycles.
4.2.1. 2-Phenylindoline 5a. 85% Isolated yield. Rf (10%
EtOAc/hexane): 0.49; Mp: 42–43 ꢁC; IR (KBr): m 3370,
3030, 1609, 1484, 1455, 1362, 1247, 1033, 927, 849 cmꢁ1
;
1H NMR (CDCl3, 300.13 MHz): 1H NMR (CDCl3,
2
3
300.13 MHz): d 2.91 (dd, JHH = 15.6 Hz, JHH = 8.7 Hz,
2
3
1H, H3), 3.36 (dd, JHH = 15.6 Hz, JHH = 8.7 Hz, 1H,
H3), 3.87 (br s, 1H, H1), 4.86 (t, JHH = 9.0 Hz, 1H, H2),
3
3
3
6.59 (d, JHH = 7.8 Hz, 1H, H4), 6.67 (td, JHH = 8.4 Hz,
4JHH = 1.0 Hz, 1H, H5), 7.00 (t, JHH = 8.1 Hz, 2H,
3
H6+H7), 7.20 (m, 3H, 2H12+H13), 7.23 (dt, 3JHH = 8.4 Hz,
4JHH = 1.8 Hz, 2H, 2H11); 13C NMR (CDCl3, 75.5 MHz):
d 39.5 (C3), 63.4 (C2), 108.8 (C4), 118.7 (C5), 124.5 (C7),
126.2 (2C11), 127.3 (C13), 127.4 (C6), 128.0 (C10), 128.5
(2C12), 144.4 (C9), 150.7 (C8). MS (EI+, m/z): 196
[(M+H)+, 100%]. Anal. Calcd for C14H13N: C, 86.12; H,
4. Experimental
4.1. General
6.71; N, 7.17. Found: C, 86.2; H, 6.6; N, 7.1.
20
½aꢀD ¼ þ65:4 (c 0.5, CHCl3) for 97% ee of the (S)-
Candida antarctica lipase type B (CAL-B, Novozyme 435,
7300 PLU/g) was a gift from Novo Nordisk Co. C. antarc-
tica lipase type A (CAL-A, Chirazyme L-5, c-f, lyophilized,
1000 U/g using tributyrin) was acquired from Roche. P.
cepacia lipase (PSL-C, 783 U/g) was obtained from Amano
Pharmaceutical Co. Chemical reagents were commercial-
ized by Aldrich, Fluka or Lancaster. The solvents were dis-
tilled over an appropriate desiccant under nitrogen. Flash
chromatography was performed using silica gel 60 (230–
240 mesh). High performance liquid chromatography
(HPLC) analyses were carried out in a Hewlett Packard
1100 chromatograph UV detector at 210 nm using a Daicel
Chiralcel OD or OB-H column (25 cm · 4.6 mm I.D.) vary-
enantiomer.
4.2.2. 2-Methyl-5-methoxyindoline 5b. 83% Isolated yield.
Rf (50% EtOAc/hexane): 0.48; Mp: 50–51 ꢁC; IR (KBr): m
3344, 2954, 2857, 2361, 1596, 1489, 1455, 1434, 1302,
1240, 1225, 1136, 1032, 944, 880, 858, 794 cmꢁ1
;
1H
3
NMR (CDCl3, 300.13 MHz): d 1.30 (d, JHH = 6.2 Hz,
2
3
3H, H10), 2.63 (dd, JHH = 15.6 Hz, JHH = 7.8 Hz, 1H,
2
3
H3), 3.13 (dd, JHH = 15.6 Hz, JHH = 8.4 Hz, 1H, H3),
3.64 (br s, 1H, NH), 3.75 (s, 3H, H11), 3.99 (m, 1H, H2),
6.59 (m, 2H, H4+H6), 6.73 (t, JHH = 1.26 Hz, 1H, H7);
13C NMR (CDCl3, 75.5 MHz): d 22.0 (C10), 38.2 (C3),
55.8 (C2), 55.9 (C11), 109.9 (C4), 111.6 (C7), 112.0 (C6),

2562
V. Gotor-Ferna´ndez et al. / Tetrahedron: Asymmetry 17 (2006) 2558–2564
3
130.7 (C5), 144.5 (C9), 153.5 (C8). MS (EI+, m/z): 164
2JHH = 10.6 Hz, JHH = 2.6 Hz, 1H, H14), 5.39 (dd,
[(M+H)+, 100%]. Anal. Calcd for C10H13NO: C, 73.59;
2JHH = 17.2 Hz, JHH = 1.5 Hz, 1H, H14), 6.05 (m, 1H,
3
3
H, 8.03; N, 8.58. Found: C, 73.6; H, 8.0; N, 8.6.
H13), 6.98 (t, JHH = 7.4 Hz, 1H, H6), 7.17 (d,
20
3
½aꢀD ¼ ꢁ14:2 (c 0.5, CHCl3) for 99% ee of the (S)-
3JHH = 6.6 Hz, 1H, H4), 7.21 (d, JHH = 7.7 Hz, 1H, H5),
enantiomer.
7.84 (br s, 1H, H7); 13C NMR (CDCl3, 75.5 MHz): d 21.3
(C10), 35.9 (C3), 55.4 (C2), 65.9 (C12), 115.5 (C7), 117.9
(C14), 122.8 (C6), 125.1 (C4), 127.5 (C5), 130.0 (C8), 132.7
(C13), 141.6 (C9), 152.8 (C11). MS (EI+, m/z): 218
[(M+H)+, 100%], 240 [(M+Na)+, 8%]. Anal. Calcd for
4.2.3. 5-Fluoro-2-methylindoline 5c. 79% Isolated yield. Rf
(20% EtOAc/hexane): 0.31; IR (NaCl): m 3375, 3038, 2964,
2927, 0360, 1609, 1487, 1446, 1379, 1235, 1215, 1125, 937,
C13H15NO2: C, 71.87; H, 6.96; N, 6.45. Found: C, 71.9;
1
860, 806 cmꢁ1; H NMR (CDCl3, 300.13 MHz): d 1.29 (d,
20
H, 6.9; N, 6.5. ½aꢀD ¼ ꢁ47:4 (c 0.5, CHCl3) for 97% ee of
2
3JHH = 6.3 Hz, 3H, H10), 2.63 (dd, JHH = 15.7 Hz,
the (R)-enantiomer.
2
3JHH = 8.0 Hz, 1H, H3), 3.12 (dd, JHH = 15.8 Hz,
3JHH = 8.6 Hz, 1H, H3), 3.43 (br s, 1H, NH), 4.00 (m,
1H, H2), 6.50 (dd, JHH = 8.4 Hz, 4.5 Hz, 1H, H4), 6.71
(m, 1H, H7), 6.82 (dd, JHH = 2.5 Hz, 1.2 Hz, 1H, H6);
13C NMR (CDCl3, 75.5 MHz): d 21.7 (C10), 37.6 (C3),
55.5 (C2), 109.0 (C4, JCF = 8.0 Hz), 111.6 (C6, JCF = 24
Hz), 112.7 (C7, JCF = 23 Hz), 130.3 (C9, JCF = 8.0 Hz),
146.4 (C8), 156.7 (C5, JCF = 233 Hz). MS (EI+, m/z): 230
[(2M)+, 100%], 152 [(M+H)+, 20%], 151 [(M)+, 12%].
4.3.2. 2-Phenylindoline allyl carbamate 6a. 97% Isolated
yield. Rf (5% EtOAc/hexane): 0.22; Mp = 68–69 ꢁC.
IR(KBr): m 2476, 3414, 3031, 2950, 2361, 1702, 1599,
1485, 1403, 1315, 1272, 1144, 1046, 997, 950, 846 cmꢁ1
;
1H NMR (CDCl3, 300.13 MHz):
d
3.04 (dd,
2JHH = 16.5 Hz, JHH = 3.0 Hz, 1H, H3), 3.76 (dd,
3
2JHH = 16.3 Hz, JHH =10.5 Hz 1H, H3), 4.65 (br s, 2H,
3
H15), 5.15 (br s, 2H, H17), 5.52 (dd, JHH = 10.2, 2.4 Hz,
1H, H2), 5.80 (br s, 1H, H16), 7.06 (t, JHH = 7.2 Hz, 1H,
H6), 7.25 (m, 7H, H4+H5+2H11+2H12+H13), 7.95 (br s,
1H, H7); 13C NMR (CDCl3, 75.5 MHz): d 37.9 (C3), 62.5
(C2), 66.0 (C15), 115.0 (C7), 117.5 (C17), 123.1 (C6), 124.9
(C4), 125.4 (2C11), 127.4, 127.8 (C5+C13), 128.7 (2C12),
129.5 (C10), 132.4 (C16), 142.7 (C8), 143.9 (C9), 153.0
(C14). MS (EI+, m/z): 302 [(M+Na)+, 100%], 280
[(M+H)+, 20%]. Anal. Calcd for C18H17NO2F: C, 77.40;
Anal. Calcd for C9H10NF: C, 71.50; H, 6.67; N, 9.26.
20
Found: C, 71.6; H, 6.7; N, 9.2. ½aꢀD ¼ ꢁ10:1 (c 0.5, CHCl3)
for 99% ee of the (S)-enantiomer.
4.2.4. 3-Methylindoline 5d. 73% Isolated yield. Rf (20%
EtOAc/hexane): 0.57; IR (NaCl): m 3379, 3050, 2960,
1
2924, 2869, 1609, 1487, 1464, 1240, 1109, 1016 cmꢁ1; H
3
NMR (CDCl3, 300.13 MHz): d 1.35 (d, JHH = 6.5 Hz,
3
H, 6.13; N, 5.01. Found: C, 77.5; H, 6.2; N, 5.0.
3H, H10), 3.13 (t, JHH = 8.7 Hz, 1H, H2), 3.39 (m, 1H,
20
3
3
½aꢀD ¼ ꢁ93:0 (c 0.5, CHCl3) for 99% ee of the (R)-
H3), 3.72 (t, JHH = 8.5 Hz, 1H, H2), 6.67 (d, JHH
=
enantiomer.
7.8 Hz, 1H, H4), 6.77 (dt, JHH = 8.4 Hz, 6.2 Hz, 1H, H5),
7.04 (dt, JHH = 8.4 Hz, 7.5 Hz, 1H, H6), 7.07 (d,
3JHH = 6.5 Hz, 1H, H7); 13C NMR (CDCl3, 75.5 MHz): d
18.5 (C10), 36.5 (C3), 55.3 (C2), 109.4 (C4), 118.6 (C5),
123.3 (C7), 127.2 (C6), 134.2 (C9), 151.1 (C8). MS
(EI+, m/z): 134 [(M+H)+, 100%]. Anal. Calcd for
4.3.3. 2-Methyl-5-methoxyindoline allyl carbamate 6b.
.98% Isolated yield. Rf (15% EtOAc/hexane): 0.31; IR
(NaCl): m 2952, 2834, 1703, 1599, 1492, 1456, 1401, 1324,
1
1275, 1207, 1134, 1051, 1033, 995, 918, 810, 760 cmꢁ1; H
3
C9H11N: C, 81.16; H, 8.32; N, 10.52. Found: C, 81.1; H,
NMR (CDCl3, 300.13 MHz): d 1.30 (d, JHH = 6.2 Hz,
20
2
3
8.2; N, 10.5. ½aꢀD ¼ ꢁ30:2 (c 0.25, CHCl3) for 99% ee of
3H, H10), 2.60 (dd, JHH = 16.2 Hz, JHH = 1.6 Hz, 1H,
2
3
the (R)-enantiomer.
H3), 3.35 (dd, JHH = 16.2 Hz, JHH = 9.7 Hz 1H, H3),
3.77 (s, 3H, H11), 4.58 (m, 1H, H2), 4.73 (d, 3JHH = 4.4 Hz,
2
3
2H, H13), 5.26 (dd, JHH = 10.6 Hz, JHH = 1.3 Hz, 1H,
4.3. Typical experimental procedure for the preparation of
racemic allyl carbamates 3 and 6a–d
2
3
H15), 5.37 (dd, JHH = 17.2 Hz, JHH = 1.6 Hz, 1H, H15),
6.01 (m, 1H, H14), 6.73 (m, 2H, H4+H6), 7.75 (br s, 1H,
H7); 13C NMR (CDCl3, 75.5 MHz): d 21.2 (C10), 36.1
(C3), 55.7 (C11+C2), 65.8 (C13), 111.4 (C4), 112.1 (C6),
115.9 (C7), 117.7 (C15), 131.4 (C5), 132.9 (C14), 135.0
(C9), 152.6 (C12), 155.9 (C8). MS (EI+, m/z): 270
[(M+Na)+, 100%], 248 [(M+H)+, 20%]. Anal. Calcd for
To a solution of the corresponding indoline (0.31 mmol) in
dry CH2Cl2 under nitrogen atmosphere and at 0 ꢁC were
added pyridine (28 lL, 0.34 mmol) and allyl chloroformate
(37 lL, 0.34 mmol). The reaction was stirred at room tem-
perature for 3 h until complete consumption of the starting
material, then the solvent was evaporated and the crude
purified by flash chromatography.
C14H17NO3: C, 68.00; H, 6.93; N, 5.66. Found: C, 68.1;
20
H, 6.8; N, 5.6. ½aꢀD ¼ ꢁ54:6 (c 0.5, CHCl3) for 95% ee of
the (R)-enantiomer.
4.3.1. 2-Methylindoline allyl carbamate 3. 98% Isolated
yield. Rf (5% EtOAc/hexane): 0.30; IR (NaCl): m 2974,
1705, 1603, 1486, 1463, 1400, 1322, 1282, 1226, 1173,
4.3.4. 5-Fluoro-2-methylindoline allyl carbamate 6c. 85%
Isolated yield. Rf (5% EtOAc/hexane): 0.29; Mp = 41–
42 ꢁC; IR: m 3557, 3415, 2968, 2933, 1701, 1612, 1488,
1140, 1104, 1048, 995, 935 cmꢁ1
;
1H NMR (CDCl3,
1398, 1297, 1275, 1127, 1050, 997, 934, 822 cmꢁ1
;
1H
3
3
300.13 MHz): d 1.30 (d, JHH = 6.5 Hz, 3H, H10), 2.65
NMR (CDCl3, 300.13 MHz): d 1.31 (d, JHH = 6.5 Hz,
2
3
2
3
(dd, JHH = 16.0 Hz, JHH = 2.2 Hz, 1H, H3), 3.38 (dd,
3H, H10), 2.62 (dd, JHH = 16.2 Hz, JHH = 1.6 Hz, 1H,
2JHH = 16.0 Hz, JHH = 9.6 Hz 1H, H3), 4.60 (m, 1H,
H2), 4.76 (d, JHH = 5.0 Hz, 2H, H12), 5.26 (dd,
H3), 3.36 (dd, JHH = 16.2 Hz, JHH = 9.4 Hz 1H, H3),
4.60 (m, 1H, H2), 4.74 (d, JHH = 5.0 Hz, 2H, H12), 5.27
3
2
3
3
3

V. Gotor-Ferna´ndez et al. / Tetrahedron: Asymmetry 17 (2006) 2558–2564
2563
2
3
(dd, JHH = 10.3 Hz, JHH = 1.3 Hz, 1H, H14), 5.37 (dd,
4.6. Enzymatic kinetic resolution of racemic 5d
2JHH = 17.2 Hz, JHH = 1.6 Hz, 1H, H14), 6.01 (m, 1H,
3
H13), 6.86 (m, 2H, H4+H6), 7.75 (br s, 1H, H7); 13C
NMR (CDCl3, 75.5 MHz): d 21.2 (C10), 35.9 (C3), 55.8
(C2), 66.0 (C12), 112.3 (C4, JCF = 24 Hz), 113.7 (C6,
JCF = 23 Hz), 116.0 (C7, JCF = 8.0 Hz), 118.0 (C14), 131.7
(C9, JCF = 8.0 Hz), 132.6 (C13), 137.5 (C8), 152.7 (C11),
159.0 (C5, JCF = 241 Hz). MS (EI+, m/z): 493 [(2M
+Na)+, 100%], 236 [(M+H)+, 10%]. Anal. Calcd for
A suspension under a nitrogen atmosphere of indoline 5d
(40 mg, 0.30 mmol), carbonate 2a (108 lL, 0.74 mmol)
and CAL-B (40 mg) in dry TBME (2 mL) was shaken at
30 ꢁC and 250 rpm during 10 h. After this time, the enzyme
was filtered off and the solvent evaporated under reduced
pressure, to give a crude that was purified by flash chroma-
tography (gradient eluent 5–20% EtOAc/hexane).
C13H14NO2F: C, 66.37; H, 6.00; N, 5.95. Found: C, 66.4;
20
H, 6.1; N, 6.0. ½aꢀD ¼ ꢁ37:3 (c 0.5, CHCl3) for 99% ee of
Acknowledgements
the (R)-enantiomer.
We thank Novo Nordisk for the generous gift of CAL-B.
Financial support of this work by the European Project
EU-04-LSHB-2003-503017 is gratefully acknowledged.
4.3.5. 3-Methylindoline allyl carbamate 6d. 87% Isolated
yield. Rf (5% EtOAc/hexane): 0.27; IR (NaCl): m 2962,
2887, 1710, 1602, 1487, 1404, 1317, 1146, 1049, 1021,
´
V.G.-F. thanks Ministerio de Educacion y Ciencia for a
932 cmꢁ1
;
1H NMR (CDCl3, 300.13 MHz): d 1.34 (d,
personal grant (Juan de la Cierva Program).
3
3JHH = 6.9 Hz, 3H, H10), 3.44 (c, JHH = 7.1 Hz, 1H,
2
3
H3), 3.59 (dd, JHH = 10.7 Hz, JHH = 6.8 Hz, 1H, H2),
4.23 (t, JHH = 9.6 Hz, 1H, H2), 4.74 (br s, 2H, H12), 5.28
3
2
2
References
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3JHH = 10.0 Hz, 1H, H14), 6.02 (m, 1H, H13), 6.99 (dt,
3JHH = 7.4 Hz, 4JHH = 1.0 Hz, 1H, H6), 7.16 (d,
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