A microwave-enhanced, lewis acid-catalyzed synthesis of 1,3-dioxolanes and oxazolines from epoxides

Article abstract of DOI:10.1002/adsc.200600516

A fast and highly regio- and stereoselective transformation of non-conventional β-lactam- b containing epoxides into the corresponding cyclic 1,3-dioxolanes and oxazolines is herein reported, using microwave irradiation as an efficient source of energy, in the presence of stoichiometric or catalytic amounts of Lewis acids, without an additional solvent. These cyclic compounds are the protected forms of diols and amino alcohols.

Full text of DOI:10.1002/adsc.200600516

FULL PAPERS
DOI: 10.1002/adsc.200600516
A Microwave-Enhanced, Lewis Acid-Catalyzed Synthesis of
1,3-Dioxolanes and Oxazolines from Epoxides
a
a,
a
a,
Fides Benfatti, Giuliana Cardillo, * Luca Gentilucci, Alessandra Tolomelli, *
a
a
Magda Monari, and Fabio Piccinelli
Department of Chemistry “G.Ciamician”, University of Bologna, Via Selmi 2, Bologna, Italy
a
Fax : (+39)-051-209-9456; e-mail: giuliana.cardillo@unibo.it or alessandra.tolomelli@unibo.it
Received: October 9, 2006; Revised: January 24, 2007
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: A fast and highly regio- and stereoselec- amounts of Lewis acids, without an additional sol-
tive transformation of non-conventional b-lactam- vent. These cyclic compounds are the protected
containing epoxides into the corresponding cyclic forms of diols and amino alcohols.
1,3-dioxolanes and oxazolines is herein reported,
using microwave irradiation as an efficient source of Keywords: dioxolanes; epoxides; lactams; Lewis
energy, in the presence of stoichiometric or catalytic acids; microwave heating
Introduction
responding acetal. Indeed, b-lactam-based structures
containing hydroxy and keto functions in the C-3 side
1
,3-Dioxolanes are widely used as protecting groups chain were recently found to be very potent cholester-
[
7]
for carbonyl functions and 1,2-diols in the synthesis of ol adsorption inhibitors (CAI).
naturally occurring compounds, and represent useful Continuing our work on the use of Lewis acids to
intermediates and end-products in pharmaceutical, carry out carbon-oxygen and carbon-nitrogen bond
fragrance and polymer industries. Moreover, to formation, we report herein the completely regio-
date, a variety of chiral cyclic acetals have been de- and stereoselective microwave-catalyzed transforma-
signed and employed as chiral auxiliaries, ligands, and tion of enantiopure and racemic b-lactam-containing
[
1]
[8]
[
2]
catalysts in a broad range of asymmetric reactions.
epoxides into the corresponding 1,3-dioxolanes and
Recently the transformation of epoxides with car- oxazolines in an extremely simple route. Microwave-
[
3]
[9]
bonyl compounds into 1,3-dioxolanes using several assisted organic synthesis is a rapidly expanding
Lewis acids and other catalysts, has received increas- area of research, since it often offers the opportunity
[4]
ing interest. However, this methodology, in most to reduce reaction times from hours to minutes and
cases, has been applied to terminal epoxides that are to increase product yield, performing solvent-free re-
known to be more reactive with respect to disubstitut- actions in compliance with green-chemistry protocols.
ed ones. In these cases, the nucleophilic attack occurs
preferentially on the less substituted methylene
group, thus avoiding problems of regio- and stereose- Results and Discussion
lectivity. For disubstituted examples, the stereochem-
istry of the reaction is accepted to proceed with inver- The starting epoxides were prepared by treating 3-
sion of the configuration at the reacting carbon posi- bromo-3-butenyl-b-lactams with an excess of meta-
[
5]
[10]
tion, while the regioselectivity is strongly influenced chloroperbenzoic acid (MCPBA) (Scheme 1).
by many factors. The epoxides were easily separated by flash chro-
As a part of an ongoing program in our laboratory matography and compound 2a was characterized by
[
11]
directed to the synthesis of potential enzymatic inhibi- single crystal X-ray analysis,
that allowed the
tors, we became interested in the introduction of hy- (1’R*,2’S*) configuration to be attributed to the
droxylated functions at the C-1’ or C-2’ position of newly-introduced stereogenic centers (Figure 1).
the alkenyl side chain of 3-bromo-3-alkenylazetidin-2-
ones. Aiming to achieve this result, we considered rac-3a with an excess of propanone used both as re-
Initial attempts involved the reaction of rac-2a and
[6]
the helpful transformation of an epoxide into the cor- agent and solvent in the presence of 1 equiv. of
1256
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 1256 – 1264

Synthesis of 1,3-Dioxolanes and Oxazolines from Epoxides
FULL PAPERS
Scheme 1. Synthesis of epoxides 2a–c and 3a–c.
Scheme 2. MW-assisted ring opening of epoxides 2a–c and
3
a–c.
1
the H NMR spectrum of the crude mixture. Al-
though no by-products and no traces of unreacted
starting material could be detected in the spectrum,
the pure dioxolanes were isolated by flash chromatog-
raphy on alumina in yields ranging from 65% to
[
13]
9
0%. The results are collected in Table 1.
The regio- and stereochemistry of the ring opening
were rigorously demonstrated. In fact, starting from
the trans epoxides 2a and 3a, the acetals 4a and 5a
were obtained, displaying a cis relationship between
1’
2’
H and H attributed on the basis of NOE experi-
ments. Furthermore, the X-ray analysis carried out on
[
14]
5a
confirmed that the ring opening occurred exclu-
sively on the less hindered C-2’ position with inver-
sion of the configuration (Figure 2).
Figure 1. Crystal structure for 2a.
Any attempt to reduce the loading of catalyst
failed, due to the strong affinity of boron trifluoride
BF ·Et O at room temperaature for 48 h. The propa- for the oxygen. For this reason we substituted
3
2
none, under BF ·Et O catalysis, is the carbonyl com- BF ·Et O with In(OTf) , a catalyst with a lower affini-
A
H
R
U
G
3
2
3
2
3
[
15]
pound most widely used to convert epoxides into the ty for oxygen.
corresponding dioxolanes, while only few examples
derived from other ketones have been reported.
Indium complexes have received increasing atten-
tion in the last few years as catalysts for a variety of
[
4d,f]
Unfortunately, the reaction with propanone furnished
a mixture containing starting material, acetal and
diol. With the aim to reduce the reaction times and
the presence of undesired derivatives, a microwave- ence of equimolar amount of boron trifluoride.
assisted methodology was applied to this reaction.
Table 1. MW-assisted ring opening of epoxides in the pres-
[a]
[b]
Entry Epoxide Product Conversion [%] Yield [%]
Under these new conditions, the carbonyl compound
[
12]
of choice was the cyclopentanone, more compatible
with microwave irradiation but unreactive with our
substrates both at room temperature or refluxing sol-
vents.
1
2
3
4
5
6
2a
2b
2c
3a
3b
3c
4a
4b
4c
5a
5b
5c
90
65
60
70
70
60
90
>95
>95
>95
>95
>95
Therefore, compounds 2a–c or 3a–c and BF ·Et O
3
2
in a 1:1 equiv. ratio and cyclopentanone (10 equivs.)
were irradiated at 200 Watt for 5 min, giving 1,3-diox-
olanes in good yield (Scheme 2). The reaction oc-
curred under complete regio- and stereocontrol, as
shown by the presence of a single diastereoisomer in
[a]
1
Conversion was calculated on the basis of H NMR spec-
tra signals.
b]
[
Yield of isolated product, after purification by chroma-
tography on alumina.
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Fides Benfatti et al.
FULL PAPERS
Scheme 3. Microwave induced reaction of cyclopentanone
with reactive epoxides.
Table 2. MW-assisted ring opening of epoxides in the presence
of catalytic amount of indium and copper Lewis acids.
Figure 2. Crystal structure for 5a.
[a]
[b]
Entry Epoxide Prod- Lewis acid
Conversion
[%]
Yield
[%]
organic reactions due to their fast coordination-disso-
uct
(%)
[
16]
ciation equilibrium. In particular, indium
A
H
R
U
G
1
2
3
4
2a
2b
2c
3a
3b
3c
2a
4a
4b
4c
5a
5b
5c
4a
In
In
In
In
In
In
A
T
E
N
(OTf) (5) >95
65
65
70
71
70
68
50
3
3
3
3
3
mide has been applied to the stereoselective epoxide
A
H
R
U
G
[17]
ring opening,
while the indium(III) triflate has
A
H
R
U
G
A
H
R
U
G
been recently applied to the thioacetalization of car-
A
H
R
U
G
[
18]
bonyl derivatives but it has never been used in the 5
transformation of epoxides to dioxolanes.
Therefore, we first tested In
(OTf) on the very re- 7
A
H
R
U
G
6
A
H
R
U
G
3
A
H
R
U
G
Cu
10)
Cu(BF )H O >95
10)
A
H
R
U
G
)H
4
2
O
>95
3
(
active cyclohexene oxide and (1R,2R)-phenylpropy-
lene oxide under several sets of conditions, varying
the loading of the L.A., the irradiation power and the
time (Scheme 3).
Best results were obtained by performing the reac-
tion of racemic cyclohexene oxide in the presence of
8
3a
5a
A
H
R
U
G
62
4
2
(
[
[
a]
1
Conversion was calculated on the basis of H NMR spectra
signals.
Yield of isolated product, after purification by chromatogra-
phy on alumina.
b]
1
mol% of In(OTf) with an irradiation power of 200
A
C
H
T
R
E
U
N
G
3
W for 1 min. When the crude reaction was diluted
with an organic solvent and filtered on a celite pad, a
mixture of diol, hemiacetal and cyclic acetal was ob- Treatment of compounds 7 and 8 with silica gel and
[
19]
tained as determined by means of GC-MS analysis.
water (10 equivs.) in ethyl acetate solution for 2 h, af-
On the other hand when the reaction mixture was forded the corresponding diols 9 and 10 in almost
submitted to aqueous work-up, the trans-diol was ex- quantitative yield. Analytical data for rac-6, 9 and 10
[21]
clusively obtained in 70% yield.
were in complete agreement with literature data.
In a similar way, the microwave induced transfor-
Under the same reaction conditions, (1R,2R)-phe-
nylpropylene oxide afforded a mixture of cis-7 and mation of 2a–c and 3a–c into the corresponding cyclo-
trans-8 cyclic acetals in a 77:23 ratio and 81% total pentanone acetals required 5% of catalyst and an ir-
yield, after chromatography on silica gel. The forma- radiation power of 500 W for 10 min (Table 2). Under
tion of the minor trans-isomer can be ascribed to the these conditions, satisfactory yields could be obtained
[
20]
partial racemization of the benzylic position. Since and product purification resulted easier. Recently,
1
2
a small difference in the H -H vicinal coupling con- copper salts have been used as catalysts for electro-
[22]
stants of the two diastereomers (7.0 Hz versus 8.4 Hz) philic activation in acylation and acetal formation.
was observed, the absolute stereochemistry of 7 and 8 When a 10% amount of Cu(BF ) ·XH O was used as
was assigned on the basis of NOESY-1D experiments. catalyst for ring opening of epoxides 2a and 3a, at
AHCTREUNG
4
2
2
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Synthesis of 1,3-Dioxolanes and Oxazolines from Epoxides
FULL PAPERS
allows the diol moiety to be obtained via the impor-
tant acetal-protected form (Scheme 4).
On the basis of these results, we accomplished the
epoxide ring opening with CH CN and PhCN as nu-
3
cleophiles aiming to obtain the corresponding oxazo-
lines, as the protected form of amino alcohols
[
24]
(
Scheme 5).
The reaction was first carried out on 2a and 3a
under conventional conditions in the presence of an
equimolar amount of boron trifluoride in CH CN
3
(
10 equivs.) that acts both as reagent and solvent, or
with PhCN (10 equivs.) in CH Cl at room tempera-
2
2
ture for 4.5 h, affording 13–16a in moderate to good
yield (Scheme 5).
Scheme 4. Hydrolysis of dioxolanes 4a–c and 5a–c.
Any attempt to perform the reaction in the pres-
ence of indium, aluminum or copper salts both at
room temperature or in refluxing acetonitrile or ben-
zonitrile failed, allowing the unreacted starting epox-
ides to be recovered. Finally, compounds 2a and 3a
were treated under microwave irradiation in the pres-
ence equimolar amount of BF ·Et O (Table 3).
3
2
Under these conditions epoxides 2a and 3a could
be transformed into the corresponding oxazolines in
short reaction times (5 min).
The microwave-assisted reaction of epoxides 2a and
a with acetonitrile in the presence of 1 equivalent of
3
BF ·Et O, was performed using a temperature pro-
3
2
gram that avoided reaching of the boiling point (en-
tries 1 and 2). Oxazolines 13a and 15a were isolated
in good yield after flash chromatography on silica gel.
The higher boiling temperature of benzonitrile al-
lowed us to react 2a and 3a at 200 W. Complete con-
Scheme 5. Reactivity of epoxide 2a and 3a with nitrile deriv- version to 14a and 16a was observed after 5 min irra-
atives.
diation (entries 3 and 4). When the reaction was per-
formed in the presence of a 10% amount of In(OTf) ,
A
C
H
T
R
E
U
N
G
3
maintaining the same irradiation parameter a very
low conversion was observed. On the other hand, by
300 W for 10 min, a lower yield of purified compound using a higher microwave irradiation power and
could be obtained after chromatography on alumina.
longer reaction times (10 min) complex mixtures of
The hydrolysis of cyclopentanone acetals to the cor- oxazoline and by-products were obtained.
responding diols was carried out under the conditions
reported in the literature for similar compounds.
In any case, the reaction afforded exclusively the
oxazoline deriving from the regioselective attack of
[
23]
Therefore, treatment of 4a–c and 5a–c in THF/H O nitrile on the less hindered C-2’ position. The regio-
2
with TFA afforded 11a–c and 12a–c in good yield, chemistry of the reaction was demonstrated by trans-
showing that the complete sequence of reactions formation of oxazolines 13a and 15a into the corre-
Table 3. MW assisted ring opening of epoxides in the presence of stoichiometric amount of boron trifluoride.
[a]
[b]
Entry
Epoxide
MW power
Reagent
Time [min]
Product
Conversion [%]
Yield [%]
[
c]
1
2
3
4
2a
3a
2a
3a
Program[
CH CN
5
5
5
5
13a
15a
14a
16a
>95
>95
>95
>95
71
70
72
65
3
c]
Program
200 W
CH CN
3
PhCN
PhCN
200 W
[
[
[
a]
b]
c]
1
Calculated on the basis of H NMR spectra signals.
After purification by chromatography on alumina.
Gradient of temperature from r.t. to 808C in 2.5 min, then T=808C for 2.5 min.
Adv. Synth. Catal. 2007, 349, 1256 – 1264
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Fides Benfatti et al.
FULL PAPERS
2
00, 300 or 600 MHz spectrometers. Chemical shifts were re-
ported as d values (ppm) relative to the solvent peak of
1
13
CDCl set at d=7.27 ( H NMR) or d=77.0 ( C NMR). LC-
3
MS analyses were performed on a liquid chromatograph
coupled with an electrospray ionization mass spectrometer
(
LC-ESI-MS), using H O/CH CN as solvent at 258C (posi-
2 3
tive scan 100–500 m/z, fragmentor 70 V, gradient elution
program from 80% water to 70% acetonitrile in 8 min).
GC-MS analysis were performed on an HP5 (cross-linked
5
% Ph Me silicone , 30 m”0.32 mm”0.25 mm thickness)
using an injection program (initial temperature 508C for
À1
2
min, then 108Cmin up to 2808C) in scan mode acquisi-
tion. Melting points were determined in open capillaries and
are uncorrected. Microanalyses were performed with an EA
1
108 CHNS-O Fisons Instrument. Microwave-assisted reac-
Scheme 6. Hydrolysis of oxazolines 13a and 15a.
tions were performed with a Milestone Mycrosynth multi-
mode apparatus, keeping irradiation power fixed and moni-
toring internal reaction temperature with a built-in ATC-FO
advanced fiber optic automatic temperature control. The re-
actions were performed in an open vessel, equipped with a
sponding N-acetylamido derivatives 17a and 18a, with
TFA (10 equivs.) in water/dichloroethane (1:9), under
microwave-assisted conditions (300 W for 5 min, refrigerator connected to a fume hood. Cyclohexene oxide
Scheme 6). The signal relative to amide proton in the and (1R,2R)-phenylpropylene oxide were purchased from
1
H NMR spectra of 17a and 18a, being a doublet cou- commercial source. Compounds 6, 9 and 10 were fully char-
acterized and their analytical data were identical to those re-
pled with the H ’ multiplet, unambiguously clarified
the product backbone, thus confirming the regiochem-
ical outcome of the oxazoline formation.
2
[21]
ported in the literature.
GeneralProcedure for the Epoxidation of 3-
Alkylidene-3-bromoazetidin-2-ones 1a–c
Conclusions
To a stirred solution of 1 (1 mmol) in CH Cl at room tem-
2
2
perature, m-chloroperbenzoic acid (1.5 equivs, 0.258 g.) was
added in one portion. The reaction mixture was stirred over-
In conclusion, for particular disubstituted complex ep-
oxides, we reported simple conditions for the regio-
and stereoselective transformation into the corre-
sponding cyclic 1,3-dioxolanes, efficient protecting
groups and precursors of diols. While the most widely
used boron trifluoride was used in an equimolar
amount, the reaction performed with indium triflate
gave comparable results in the presence of a 5%
night and then diluted with a saturated solution of K CO3
2
(
5 mL) and CH Cl (5 mL). The two phases were separated,
2 2
the organic layer was dried over Na SO and solvent was re-
2
4
moved under reduced pressure. Compounds 2 and 3 were
isolated by flash chromatography on silica gel (cyclohexane/
ethyl acetate 9/1 as eluant).
2a: mp 145–1478C; HPLC-MS: R =14.5 min, (M+1)=
t
amount of catalyst. Applying the same methodology 386/388, (M+Na)=408/410 m/z; IR (nujol): n=3073, 2959,
À1
to the reaction of epoxides with nitriles in the pres- 2930, 1771, 1654, 1455, 1395, 1355, 1157, 1124, 1077 cm ;
1
H NMR (600 MHz, CDCl ): d=1.05 (t, 3H, J=7.2 Hz,
ence of boron trifluoride, the corresponding oxazo-
lines were obtained with complete regio- and stereo-
control.
Finally, the use of microwave irradiation as efficient
source of energy, without additional solvent, lowered
the environmental impact of the transformation, al-
lowing us to accomplish epoxide ring opening in a
few minutes.
3
CH ), 1.53–1.77 (m, 2H, CH CH ), 3.27 (1H, d, J=2.2 Hz,
BrCHCHO), 3.57 (1H, dt, J=2.2, 5.6 Hz, CH CHO), 3.91
(
3
2
3
2
d, 1H, J=15.0 Hz, CH Ph), 4.78 (s, 1H, CHPh), 4.99 (d,
2
1
H, J=15.0 Hz, CH Ph), 7.18–7.43 (m, 10H, CHAr);
2
13
C NMR (150 MHz, CDCl ): d=9.6, 24.6, 44.9, 58.7, 59.5,
3
6
1
8.4, 127.7, 127.9, 128.2, 128.4, 128.7, 129.1, 133.7, 133.9,
63.5; anal. calcd. for C H BrNO : C 62.19, H 5.22, N 3.63;
2
0
20
2
found: C 62.21, H 5.23, N 3.62.
a: HPLC-MS: R =15.2 min, (M+1)=386/388, (M+
3
t
Na)=408/410 m/z; IR (neat): n=2962, 2928, 1775, 1494,
À1
1
1
454, 1392, 1351, 1147, 1072 cm ; H NMR (600 MHz,
ExperimentalSection
CDCl ): d=1.02 (t, 3H, J=7.6 Hz, CH ), 1.45–1.82 (m, 2H,
3
3
CH CH ), 2.89 (1H, dt, J=1.8, 5.6 Hz, CH CHO), 3.45 (1H,
2
3
2
GeneralRemarks
d, J=1.8 Hz, BrCHCHO), 3.93 (d, 1H, J=15.0 Hz, CH Ph),
2
All chemicals were purchased from commercial suppliers
and used without further purification. Anhydrous solvents
were purchased in sure seal bottles over molecular sieves
and used without further drying. Flash chromatography was
performed on alumina (150 mesh, neutral deactivated) or
silica gel (230–400 mesh). NMR spectra were recorded with
4.59 (s, 1H, CHPh), 4.97 (d, 1H, J=15.0 Hz, CH Ph), 7.16–
2
1
3
7.44 (m, 10H, CHAr); C NMR (150 MHz, CDCl ): d=9.4,
3
24.2, 44.9, 57.3, 58.9, 59.5, 68.8, 127.8, 127.9, 128.1, 128.4,
128.7, 128.9, 133.8, 134.0, 164.0; anal. calcd. for
C H BrNO : C 62.19, H 5.22, N 3.63; found: C 62.17, H
2
0
20
2
5.24, N 3.66.
1260
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Adv. Synth. Catal. 2007, 349, 1256 – 1264

Synthesis of 1,3-Dioxolanes and Oxazolines from Epoxides
FULL PAPERS
Boron Trifluoride-Catalyzed Synthesis of Acetals 4a–
c and 5a–c under Microwave-Assisted Conditions.
to microwave irradiation (power 200 W) for one minute and
then was diluted with ethyl acetate (20 mL) and washed
twice with water (20 mL). The two phases were separated,
the organic layer was dried over Na SO and solvent was re-
moved under reduced pressure. Compounds 6, 7, 8 were iso-
lated by flash chromatography on silica gel (cyclohexane/
ethyl acetate, 98/2 as eluant). Treatment of 7 and 8 with
Epoxide 2 or 3 (1 mmol) was diluted in cyclopentanone
2
4
(
10 equivs., 10 mmol, 0.88 mL) and BF ·Et O (1 equiv.,
3 2
1
mmol, 0.123 mL) was added in one portion. The mixture
was submitted to microwave irradiation (power 200 W) for
five minutes and then was diluted with ethyl acetate
H O (10 equivs., 0.18 mL) and silica gel (0.1 g) in EtOAc
2
(
20 mL) and washed twice with water (20 mL). The two
(
5 mL) allowed us to isolate, after filtration of the solid cata-
phases were separated, the organic layer was dried over
Na SO and solvent was removed under reduced pressure.
lyst and solvent removal, diols 9 and 10 in almost quantita-
tive yields. Analytical data for rac-6, (1S,2R)-9 and (1R,2R)-
2
4
Compounds 4 and 5 were isolated by flash chromatography
on alumina (cyclohexane/ethyl acetate, 98/2 as eluant).
1
ture.
0 were in agreement with the data reported in the litera-
[21]
2
0
AHCTREUNG
(1S,2R)-7: [a] : +14.1 (c 9, CHCl ); GC-MS (EI): R =
D
3
t
Indium Triflate-Catalyzed Synthesis of Acetals 4a–c
and 5a–c under Microwave-Assisted Conditions
16.52 min, m/z=218 (10), 189 (65), 174 (100), 117 (80), 105
(82), 91 (95); IR (neat): n=3582, 3064, 3029, 2968, 1949,
À1
1
1
495, 1453, 1332, 1110 cm ; H NMR (300 MHz, CDCl ):
3
Epoxide 2 or 3 (1 mmol) was diluted in cyclopentanone
d=0.87 (t, 3H, J=6.3 Hz, CHCH ), 1.78–2.29 (m, 8H, CH2
3
(
10 equiv, 10 mmol, 0.88 mL) and In
A
H
R
U
G
cyclopentane), 4.49 (dq, 1H, J=6.6, 6.3 Hz, CHCH ), 5.10
3
0.05 mmol, 28 mg) was added in one portion. The mixture
(d, 1H, J=6.6 Hz, CHPh), 7.25–7.45 (m, 5H, CHAr);
was submitted to microwave irradiation (power 500 W) for
ten minutes and then was diluted with ethyl acetate (20 mL)
and washed twice with water (20 mL). The two phases were
separated, the organic layer was dried over Na SO and sol-
13
C NMR (75 MHz, CDCl ): d=16.4, 23.1, 24.0, 36.5, 36.7,
3
7
4.1, 80.1, 118.0, 126.7, 127.5, 127.9, 138.4; anal. calcd. for
C H O : C 77.03, H 8.31; found: C 77.07, H 8.28.
1
4
18
2
20
2
4
A
H
R
U
G
vent was removed under reduced pressure. Compounds 4
and 5 were isolated by flash chromatography on alumina
1
6.25 min, m/z=218 (20), 189 (80), 174 (65), 117 (100), 105
(
90), 91 (95); IR (neat): n=3629, 3088, 2872, 1950, 1654,
(
cyclohexane/ethyl acetate, 98/2 as eluant).
À1
1
1
494, 1433, 1367, 1207 cm ; H NMR (300 MHz, CDCl ):
3
4
a: HPLC-MS: R =23.3 min, (M+1)=470/472, (M+
t
d=1.35 (t, 3H, J=6.0 Hz, CHCH ), 1.78–2.20 (m, 8H, CH2
cyclopentane), 3.87 (dq, 1H, J=8.4, 6.0 Hz, CHCH ), 4.43
3
Na)=492/494 m/z; IR (neat): n=3087, 3064, 3031, 2964,
3
2
1
3
931, 2874, 2356, 2323, 2252, 1772, 1655, 1616, 1496, 1455,
(d, 1H, J=8.4 Hz, CHPh), 7.20–7.45 (m, 5H, CHAr);
À1
1
395, 1115 cm ; H NMR (300 MHz, CDCl ): d=1.07 (t,
13
3
C NMR (75 MHz, CDCl ): d=16.2, 23.3, 23.5, 37.5(2C),
3
H, J=7.5 Hz, CHCH CH ), 1.65–1.80 (m, 6H,
2
3
7
9.2, 84.7, 118.5, 126.4, 128.0, 128.4, 137.9; anal. calcd. for
CH ciclopentane), 1.87–2.04 (m, 3H, CHCH2
+
2
C H O : C 77.03, H 8.31; found: C 77.00, H 8.33.
1
4
18
2
CH cyclopentane), 2.22–2.38 (m, 1H, CH CH ), 3.95 (1H, d,
2
2
3
J=15 Hz, CH Ph), 4.06 (m, 1H, OCHCH CH ), 4.14 (d,
2
2
3
1
H, J=6.6 Hz, BrCCHO), 4.95 (s, 1H, CHPh), 6.00 (d, 1H,
General Procedure for the Hydrolysis of Acetals 4a–c
and 5a–c
13
J=15 Hz, CH Ph), 7.14–7.49 (m,10H, CHAr); C NMR
2
(75 MHz, CDCl ): d=11.3, 23.4, 23.5, 23.6, 37.3 (2C), 44.5,
3
6
1
6
3.3, 63.6, 79.7, 80.8, 118.8, 127.8, 128.1, 128.4, 128.8, 128.9,
29.0, 134.3, 139.5, 168.4; anal. calcd. for C H BrNO : C
To a stirred solution of 4 or 5 (1 mmol) in THF/H O (1/1 so-
2
lution, 5 mL) at room temperature, trifluoroacetic acid
(10 equiv, 10 mmol, 0.74 mL) was added in one portion. The
reaction was stirred overnight and then THF was removed
under reduced pressure. The aqueous residue was diluted
with water (5 mL) and extracted twice with CH Cl (10 mL).
2
5
28
3
3.83, H 6.00, N 2.98; found: C 63.85, H 6.01, N 2.94.
a: mp 118–1208C; HPLC-MS: r =13.28 min, (M+1)=
5
t
470/472 m/z ; IR (nujol): n=2930, 2874, 2855, 1777, 1655,
À1
1
1637, 1457, 1425, 1215, 1151, 1109, 1068 cm ; H NMR
2
2
(
1
300 MHz, CDCl ): d=0.98 (t, 3H, J=7.4 Hz, CHCH CH ),
.20–1.90 (m, 10H, CHCH2 + CH2 cyclopentane), 3.74
The two phases were separated, the organic layer was dried
over Na SO and solvent was removed under reduced pres-
3
2
3
2
4
(
4
1H, d, J=14.8 Hz, CH Ph), 4.04 (m, 1H, OCHCH CH ),
.61 (d, 1H, J=6.4 Hz, BrCCHO), 4.93 (d, 1H, J=14.8 Hz,
sure. Compounds 11 and 12 were isolated by flash chroma-
tography on silica gel (cyclohexane/ethyl acetate, 7/3 as
eluant).
2
2
3
CH Ph), 4.94 (s, 1H, CHPh), 7.15–7.60 (m,10H, CHAr);
2
13
C NMR (75 MHz, CDCl ): d=11.3, 23.4, 23.5, 24.0, 36.1,
11a: HPLC-MS: R =9.36 min, (MÀHBr +1)=324 m/z;
3
t
3
1
6.8, 44.4, 60.8, 69.1, 78.0, 79.7, 118.8, 128.3, 128.6, 128.9,
29.1, 129.3, 129.5, 133.6, 134.4, 165.3; anal. calcd. for
IR (neat): n=3487, 2934, 2911, 2874, 2350, 2321, 2199, 1744,
À1
1
1650, 1600, 1496, 1425, 1381, 1112 cm ; H NMR (300 MHz,
C H BrNO : C 63.83, H 6.00, N 2.98; found: C 63.80, H
CDCl ): d=0.88 (t, 3H, J=7.5 Hz, CHCH CH ), 1.56–1.80
25
28
3
3
2
3
5.97, N 2.97.
(m, 2H, CHCH CH ), 3.64 (m, 1H, CHCH CH ), 3.85 (1H,
2 3 2 3
d, J=15.5 Hz, CH Ph), 4.49 (s, 1H, CHPh), 4.61 (d, 1H, J=
2
1
7
2
1
5.5 Hz, CH Ph), 4.78 (d, 1H, J=6.5 Hz, BrCCHO), 7.21–
Indium Triflate-Catalyzed Synthesis of 6, 7 and 8
under Microwave-Assisted Conditions; Hydrolysis of
2
1
3
.65 (m, 10H, CHAr); C NMR (75 MHz, CDCl ): d=9.0,
3
6.1, 30.3, 50.2, 66.6, 83.0, 100.0, 127.7, 129.7, 129.8, 129.9,
30.0 (2), 130.7, 131.6, 161.0; anal. calcd. for C H BrNO :
7
and 8
2
0
22
3
Cyclohexene oxide (1 mmol) or (1R,2R)-phenylpropylene
C 59.42, H 5.48, N 3.46; found: C 59.41, H 5.44, N 3.49.
oxide (1 mmol) was diluted in cyclopentanone (10 equivs,
12a: HPLC-MS: R =9.57 min, (M+1)=404/406, (M+
t
1
6
0 mmol, 0.88 mL) and In
mg) was added in one portion. The mixture was submitted
A
H
R
U
G
Na)=426/428 m/z; IR (neat): n=3352, 2945, 2924, 2853,
2095, 1712, 1673, 1614, 1456, 1377, 1112 cm ; H NMR
3
À1
1
Adv. Synth. Catal. 2007, 349, 1256 – 1264
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1261

Fides Benfatti et al.
FULL PAPERS
(
300 MHz, CDCl ): d=1.03 (t, 3H, J=7.2 Hz, CHCH CH ),
calcd. for C H BrN O : C 66.26, H 5.15, N 5.72; found: C
3
2
3
27 25
2
2
1
3
.45–1.80 (m, 2H, CHCH CH ), 2.40–2.80 (bs, 2H, OH),
.59 (d, 1H, J=7.5 Hz, BrCCHO), 3.78 (m, 1H,
66.25, H 5.12, N 5.74.
2
3
15a: HPLC-MS: R =10.29 min, (M+1)=427/429 m/z; IR
t
CHCH CH ), 3.95 (1H, d, J=15 Hz, CH Ph), 4.76 (s, 1H,
(neat): n=2932, 2875, 1776, 1679, 1547, 1495, 1455, 1387,
2
3
2
À1
1
CHPh), 4.96 (d, 1H, J=15 Hz, CH Ph), 7.26–7.43 (m, 10H,
1399, 1219 cm ; H NMR (300 MHz, CDCl ): d=1.06 (t,
2
3
13
CHAr); C NMR (75 MHz, CDCl ): d=9.6, 25.1, 30.3, 45.3,
3H, J=7.2 Hz, CHCH CH ), 1.78 (m, 2H, CHCH CH ),
3
2
3
2
3
6
1
4.9, 74.3, 90.7, 128.0, 128.3, 128.5, 128.6, 129.0, 129.1, 130.0,
33.8, 171.2; anal. calcd. for C H BrNO : C 59.42, H 5.48,
1.81 (s, 3H), 3.68 (d, 1H, J=15 Hz, CH Ph), 4.06 (m, 1H,
2
NCHCH CH ), 4.78 (s, 1H, CHPh), 5.00 (d, 1H, J=15 Hz,
2
0
22
3
2
3
N 3.46; found: C 59.40, H 5.47, N 3.45.
CH Ph), 5.11 (d, 1H, J=9.6 Hz, BrCCHO), 7.18–7.48
2
13
(
m,10H, CHAr); C NMR (75 MHz, CDCl ): d=12.1, 13.8,
3
2
1
5.6, 44.5, 61.2, 67.5, 70.1, 82.1, 128.1, 128.4, 128.5, 128.8,
29.2, 129.5, 132.9, 134.2, 163.2, 164.6; anal. calcd. for
Boron Trifluoride-Catalyzed Synthesis of Oxazolines
3–16a under ConventionalConditions
C H BrN O : C 61.83, H 5.42, N 6.56; found: C 61.80, H
1
22 23
2
2
5
.43, N 6.55.
16a: HPLC-MS: r =12.35 min, (M+1)=489/491, (M+
Epoxide 2a or 3a (1 mmol) was diluted in CH Cl (10 mL)
2
2
t
and acetonitrile or benzonitrile (10 equiv) and BF ·Et O
3
2
Na)=511/513, (2M+Na)=999/1001 m/z; IR (neat): n=
À1
(
1 equiv., 1 mmol, 0.123 mL) were added in one portion.
2
924, 2853, 1777, 1655, 1495, 1466, 1399, 1363, cm ;
1
The mixture was stirred ar room temparature for four hours
and then was washed twice with water (20 mL). The two
phases were separated, the organic layer was dried over
H NMR (300 MHz, CDCl ): d=1.14 (t, 3H, J=7.2 Hz,
3
CHCH CH ), 1.76 (m, 2H, CHCH CH ), 3.77 (d, 1H, J=
1
2
3
2
3
5 Hz, CH Ph), 4.28 (m, 1H, NCHCH CH ), 4.86 (s, 1H,
2
2
3
Na SO and solvent was removed under reduced pressure.
2
4
CHPh), 5.01 (d, 1H, J=15 Hz, CH Ph), 5.30 (d, 1H, J=
2
13
Compounds 13–16a were isolated by flash chromatography
on silica gel (cyclohexane/ethyl acetate, 95/5 as eluant).
9
Hz, BrCCHO), 7.11–7.57 (m,15H, CHAr); C NMR
(75 MHz, CDCl ): d=11.8, 14.1, 22.7, 44.5, 61.6, 70.2, 82.3,
3
1
1
27.7, 127.9, 128.4, 128.5, 128.7, 128.9, 129.3, 129.5, 131.7,
32.0, 132.9, 133.9, 162.3, 164.6; anal. calcd. for
Boron Trifluoride-Catalyzed Synthesis of Oxazolines
C H BrN O : C 66.26, H 5.15, N 5.72; found: C 66.28, H
5.18, N 5.69.
27 25 2 2
13–16a under Microwave-Assisted Conditions
Epoxide 2a or 3a (1 mmol) was diluted in acetonitrile or
benzonitrile (10 equiv) and BF ·Et O (1 equiv., 1 mmol,
3
2
General Procedure for the Hydrolysis of Oxazolines
3a and 15a
0.123 mL) was added in one portion. The mixture was sub-
1
mitted to microwave irradiation (for acetonitrile: gradient
of temperature from room temperature to 808C in 2.5 min,
then T=808C for 2.5 min; for benzonitrile: power 200 W
for 5 min) and then was diluted with ethyl acetate (20 mL)
and washed twice with water (20 mL). The two phases were
separated, the organic layer was dried over Na SO and sol-
To a stirred solution of 13a or 15a (1 mmol) in dichloro-
ethane/H O (9/1 solution, 5 mL) at room temperature, tri-
2
fluoroacetic acid (10 equivs, 10 mmol, 0.74 mL) was added
in one portion. The mixture was submitted to microwave ir-
radiation (power 300 W) for five minutes The solution was
2
4
vent was removed under reduced pressure. Compounds 13–
6a were isolated by flash chromatography on silica gel (cy-
clohexane/ethyl acetate 95/5 as eluant).
3a: HPLC-MS: R =10.25 min, (M+1)=427/429 m/z; IR
diluted with water (5 mL) and extracted twice with CH Cl2
2
1
(10 mL). The two phases were separated, the organic layer
was dried over Na SO and solvent was removed under re-
2
4
1
duced pressure. Compounds 17a and 18a were isolated by
flash chromatography on silica gel (cyclohexane/ethyl ace-
tate, 1/1 as eluant).
t
(
neat): n=2973, 2923, 1771, 1699, 1635, 1558, 1506,
À1
1
1
7
3
456 cm ; H NMR (300 MHz, CDCl ): d=1.08 (t, 3H, J=
3
.4 Hz, CHCH CH ), 1.65 (m, 2H, CHCH CH ), 1.94 (s,
17a: HPLC-MS: R =8.62 min, (M+1)=445/447 m/z; IR
2
3
2
3
t
H), 3.83 (d, 1H, J=15 Hz, CH Ph), 4.02 (m, 1H,
(neat): n=3300, 2924, 2853, 1752, 1701, 1654, 1640, 1457,
2
À1
1
NCHCH CH ), 4.74 (s, 1H, CHPh), 4.81 (d, 1H, J=9 Hz,
1376, 1266 cm ; H NMR (300 MHz, C D ): d=0.85 (t, 3H,
2
3
6 6
BrCCHO), 4.98 1 (d, 1H, J=15 Hz, CH Ph), 7.20–7.46
J=7.5 Hz, CHCH CH ), 1.62 (s, 3H), 1.80–2.0 (m, 2H,
2 3
2
3
(
m,10H, CHAr); C NMR (75 MHz, CDCl ): d=12.2, 13.9,
CHCH CH ), 3.68 (d, 1H, J=15.3 Hz, CH Ph), 4.03 (m, 1H,
3
2
3
2
2
1
4.5, 44.9, 63.4, 69.1, 70.9, 83.2, 128.1, 128.3, 128.5, 128.7,
28.8, 129.3, 132.8, 134.3, 165.1, 167.0; anal. calcd. for
NCHCH CH ), 4.11 (bs, 1H, BrCCHO), 4.69 (d, 1H, J=
2 3
15.3 Hz, CH Ph), 5.31 (s, 1H, CHPh), 5.32 (d, 1H, J=
2
1
3
C H BrN O : C 61.83, H 5.42, N 6.56; found: C 61.85, H
8.7 Hz, NH), 6.85–7.25 (m,10H, CHAr); C NMR (75 MHz,
22
23
2
2
5.41, N 6.52.
CDCl ): d=11.4, 23.3, 26.9, 45.3, 56.6, 60.4, 62.8, 73.0, 127.9,
3
1
4a: HPLC-MS: R =12.56 min, (M+1)=489/491, (M+
128.2, 128.3, 128.5, 128.7, 128.8, 134.3, 134.5, 165.4, 172.8;
anal. calcd. for C H BrN O : C 59.33, H 5.66, N 6.29;
t
Na)=511/513, (2M+Na)=999/1001 m/z; IR (neat): n=
2
2
25
2
3
2
1
7
1
924, 2853, 1771, 1654, 1462 1376, 1344, 1277, 1100,
found: C 59.31, H 5.68, N 6.31.
À1
1
088 cm ; H NMR (300 MHz, CDCl ): d=1.33 (t, 3H, J=
18a: HPLC-MS: R =8.84 min, (M+1)=445/447 m/z; IR
3
t
.2 Hz, CHCH CH ), 2.25 (m, 2H, CHCH CH ), 3.43 (d,
(neat): n=3345, 2964, 1758, 1637, 1560, 1400, 1261, 1095,
2
3
2
3
À1
1
H, J=15 Hz, CH Ph), 4.10 (m, 1H, NCHCH CH ), 4.66
1023 cm ; H NMR (300 MHz, CDCl ): d=1.02(t, 3H, J=
2
2
3
3
(
d, 1H, J=9 Hz, BrCCHO), 4.80 (d, 1H, J=15 Hz, CH Ph),
7.5 Hz, CHCH CH ), 1.70–1.85 (m, 2H, CHCH CH ), 2.14
2
2
3
2
3
4
.92 (s, 1H, CHPh), 6.91–7.0 (m,13H, CHAr), 8.0 (m,2H,
(s, 3H), 3.60–3.80 (bs, 1H, OH); 4.02 (d, 1H, J=15.3 Hz,
CH Ph), 4.07–4.15 (m, 2H, NCHCH CH +BrCCHO), 5.00
13
CHAr); C NMR (75 MHz, CDCl ): d=12.0, 13.0, 24.8,
3
2
2
3
4
1
4.8, 63.6, 70.7, 83.7, 128.0, 128.2, 128.3, 128.5, 128.6, 128.7,
28.9, 129.3, 131.8, 133.9, 134.1, 136.8, 162.1, 164.9; anal.
(s, 1H, CHPh), 5.01 (d, 1H, J=15.3 Hz, CH Ph), 6.56 (d,
2
13
1H, J=7.8 Hz, NH), 7.20–7.60 (m,10H, CHAr); C NMR
1262
asc.wiley-vch.de
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 1256 – 1264

Synthesis of 1,3-Dioxolanes and Oxazolines from Epoxides
FULL PAPERS
(
7
1
75 MHz, CDCl ): d=11.4, 23.3, 26.9, 45.3, 56.6, 60.4, 62.8,
[4] For recent examples see: a) A. Solladiꢁ-Cavallo, E.
Choucair, M. Balaz, P. Lupatelli, C. Bonini, N. Di Bla-
sio, Eur. J. Org. Chem. 2006, 3007–3011; b) V. Mirkha-
ni, S. Tangestaninejad, B. Yadollahi, L. Alipanah, Catal.
Lett. 2003, 91, 129–132; c) L. Guixian, B. Wang, J.
Wang, Y. Ding, L. Yan, J. Suo, J. Mol. Cat. A: Chemical
3
3.0, 127.9, 128.2, 128.3, 128.5, 128.7, 128.8, 134.3, 134.5,
65.4, 172.8; anal. calcd. for C H BrN O : C 59.33, H 5.66,
2
2
25
2
3
N 6.29; found: C 59.36, H 5.65, N 6.26.
X-ray Crystallographic Study
2
005, 236, 72–76; d) A. Procopio, R. Dalpozzo, A.
Crystal data for 2a: C H Br NO , M=386.28, monoclinic
P21/c, a=8.8729(11), b=19.734(2), c=21.236(3) Š, b=
9
2
reflections collected, 4235 I>2s(I). Final R1=0.0474,
wR2=0.1260, GOF=0.769. CCDC 286004. Crystallographic
data (excluding structure factors) for the structure reported
in this paper has been deposited with the Cambridge Crys-
tallographic Data Centre as supplementary publication no.
CCDC 286004. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
2
0
20
1
2
De Nino, L. Maiuolo, M. Nardi, B. Russo, Adv. Synth.
Catal. 2005, 347, 1447–1450; e) Z. Zuolin, J. H. Espen-
son, Organometallics 1997, 16, 3658–3663; f) J. M. Con-
cellon, J. R. Suarez, S. Garcia-Granda, M. R. Diaz,
Org. Lett. 2005, 7, 247–250.
À3
2.613(2), V=3714.5(8) Š3, Z=8, 1x=1.381 Mgm , m=
À1
.224 mm , F
A
C
H
T
R
E
U
N
G
(000)=1584, T=296(2) K, q =25.40, 34970
max
[
[
[
5] B. N. Blanckett, J. M. Coxon, M. P. Hartshorn, A. J.
Lewis, G. R. Little, G. J. Wright, Tetrahedron 1970, 26,
1
311–1313.
6] F. Benfatti, G. Cardillo, S. Fabbroni, L. Gentilucci, R.
Perciaccante, F. Piccinelli, A. Tolomelli, Synthesis 2005,
6
1–70.
7] a) J. W. Clader, Curr. Top. Med.Chem. 2005, 5, 231–
33; b) J. W. Clader, Curr. Top. Med.Chem. 2005, 5,
243–256; c) J. W. Clader, Science 2004, 303, 1201–
204; d) L. Kvaerno, M. Werder, H. Hauser, E. M. Car-
reira, J. Med. Chem. 2005, 48, 6035–6053.
CB2 1EZ, UK [Fax: int. code + 44(1223)336–033; E-mail:
deposit@ccdc.cam.ac.uk].
A
T
E
N
2
Crystal data for 5a: C H Br NO , M=470.39, triclinic
2
5
28
1
3
¯
P1,
a=98.500(2),
145.9(2) Š3, Z=2, 1x=1.363 Mgm , m=1.819 mm , F-
a=10.3810(10),
b=10.9710(10),
c=12.426(2 Š,
1
b=106.067(2),
g=117.1720(10),
V=
À3
À1
1
A
C
H
T
R
E
U
N
G
(000)=488, T=296(2) K, q =28.69, 8540 reflections col-
[8] G. Cardillo, S. Fabbroni, L. Gentilucci, R. Perciaccante,
A. Tolomelli, Adv. Synth. Catal. 2005, 347, 833–838,
and references cited therein.
max
lected, 3629 I>2s(I). Final R1=0.0409, wR2=0.1088,
GOF=1.028. CCDC 621038. Crystallographic data (exclud-
ing structure factors) for the structure reported in this paper
has been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC
[9] a) C. O. Kappe, Angew. Chem. Int. Ed. 2004, 43, 6250–
6284; b) C. O. Kappe, A. Stadler, Microwaves in Organ-
ic and Medicinal Chemistry, Methods and Principles in
Medicinal Chemistry, Vol. 25, (Eds.: R. Mannhold, H.
Kubinyi, G. Folkers), Wiley-VCH, Weinheim, 2005;
c) B. L. Hayes, Aldrichimica Acta 2004, 37, 66–76;
d) B. L. Hayes, Microwave Synthesis: Chemistry at the
Speed of Light, 1st edn., CEM Publishing, Matthews,
NC, 2002.
6
21038. Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB2
EZ, UK [Fax: int. code + 44(1223)336–033; E-mail: de-
1
ACHTREUNG
posit@ccdc.cam.ac.uk].
[
[
10] F . Benfatti, G. Cardillo, L. Gentilucci, R. Perciaccante,
Acknowledgements
A. Tolomelli, Synlett 2005, 2204–2206.
11] Crystal data for 2a have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary
publication no. CCDC 286004.
12] Boiling point 130–1318C.
13] In some cases, a small amount of diol could be isolated
from flash chromatography.
We thank MIUR (PRIN 2004 prot.n. 2004031072), CNR-
ISOF and University of Bologna (Funds for selected topics)
for financial support. Mr. Andrea Garelli is gratefully ac-
knowledged for the LC-ESI-MS analysis.
[
[
[
14] Crystal data for 5a have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary
publication no. CCDC 621038.
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[
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