Indium triflate catalyzed rearrangement of aryl-substituted cyclopropyl carbinols to 1,4-disubstituted 1,3-butadienes

Article abstract of DOI:10.1002/ejoc.200600037

Aryl-substituted cyclopropyl carbinol derivatives undergo a facile stereoselective rearrangement catalyzed by In(OTf)₃ in dichloromethane under sonication to produce the substituted conjugated all-trans-butadienes. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejoc.200600037

FULL PAPER
DOI: 10.1002/ejoc.200600037
Indium Triflate Catalyzed Rearrangement of Aryl-Substituted Cyclopropyl
Carbinols to 1,4-Disubstituted 1,3-Butadienes
[a]
[a]
Brindaban C. Ranu* and Subhash Banerjee
Keywords: Carbinols / Homogeneous catalysis / Indium / Rearrangement / Sonication
Aryl-substituted cyclopropyl carbinol derivatives undergo a
facile stereoselective rearrangement catalyzed by In(OTf) in
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
3
dichloromethane under sonication to produce the substituted
conjugated all-trans-butadienes.
[
6a]
Introduction
and pressure
or heating under reflux in DMSO for
[
6b]
5
h,
to the best of our knowledge there is no report of
The importance of indium reagents in organic synthesis
has been well demonstrated through novel protocols for
carbon–carbon bond formation, rearrangements and a vari-
ety of other useful transformations over the past few
this rearrangement with a Lewis acid under ambient condi-
tions; this protocol meets this requirement. The experimen-
tal procedure for this transformation is very simple. The
cyclopropyl carbinol was sonicated in the presence of a
[
1]
[2]
years, and interest in this area is continuing. Indium(III)
catalytic amount (10 mol-%) of In(OTf) in dichlorometh-
3
halides, including indium(III) triflate,[
3c,3d]
have also been
ane for a set period of time (TLC). The product was then
isolated by extraction with diethyl ether.
A variety of structurally diverse aryl-substituted cy-
clopropyl carbinol derivatives undergo this facile rearrange-
used as potential Lewis acids in a variety of useful reac-
[
3]
tions. As part of our activities in indium-mediated reac-
[
4]
[5]
tions we are constantly looking for new indium reagents
for novel applications in organic synthesis. We demonstrate
here the use of indium triflate as an efficient Lewis acid
catalyst for the rearrangement of cyclopropyl carbinol de-
rivatives, leading to the stereoselective synthesis of conju-
gated butadienes (Scheme 1).
ment catalyzed by In(OTf) to provide the aryl-substituted
3
all-trans-butadienes. The results are summarized in Table 1.
The trans configuration of both the double bonds was es-
tablished by the coupling constant (J) values of the olefinic
protons. All these products (except two) are crystalline sol-
ids and the observed melting points of these compounds
are also in good agreement with the reported values of
known trans isomers. Various substituents like Cl, OMe, di-
oxymethylene, thiomethyl and benzyl remained unaffected
under the reaction conditions. Sensitive molecules such as
furan and thiophene derivatives (Entries 11 and 12) also
survived in the reaction medium. However, the reactions
with alkyl (2-alkyl cyclopropyl) carbinols are messy and
lead to a mixture of unidentified products; these reactions
have not been pursued further.
Scheme 1. Rearrangement of cyclopropyl carbinols.
In general, the reactions are reasonably fast (25–45 min),
and 10 mol-% of In(OTf) is sufficient to push the reaction
forward. The reactions can also be accomplished by stirring
Results and Discussion
3
Although cyclopropyl carbinols have been reported to at room temperature for a longer time (4–6 h). However, in
undergo rearrangement to conjugated butadienes on treat- the absence of In(OTf) the reaction did not proceed at all
3
ment with an acid catalyst, KHSO at elevated temperature either under sonication or stirring at room temperature.
4
Thus, for the best result in terms of reaction time sonication
[
a] Department of Organic Chemistry, Indian Association for the was the obvious choice. Methylene chloride was found to be
Cultivation of Science,
most suitable for this reaction among other solvents (THF,
Jadavpur, Kolkata 700032, India
Fax: +91-33-2473-2805
E-mail: ocbcr@iacs.res.in
CH CN). The widely used indium trichloride also failed to
3
initiate this reaction. The products were obtained in high
3012
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 3012–3015

Rearrangement of Aryl-Substituted Cyclopropyl Carbinols
Table 1. In(OTf) -catalyzed rearrangement of cyclopropyl carbinols to butadienes.
FULL PAPER
3
a] Yields refer to those of pure isolated products characterized spectroscopically (IR, H and 13C NMR).
1
[
yields and purity after just a short filtration followed by Conclusion
chromatography or recrystallization of the crude products.
No side-product was isolated in any reaction.
The present procedure using indium(III) triflate as a cat-
alyst for the rearrangement of cyclopropyl carbinol deriva-
tives provides a novel protocol for the synthesis of substi-
tuted conjugated all-trans-butadiene systems. This pro-
cedure offers marked improvements with regard to opera-
tional simplicity, stereoselectivity (exclusively trans) and
high isolated yields (80–95%) of products, considerably fast
reaction time (25–45 min), and milder reaction conditions.
Presumably, indium triflate, which is a Lewis acid, polar-
izes the C–O bond of the cyclopropyl carbinol derivative
and thus facilitates cleavage of the cyclopropyl moiety to
produce the benzylic carbonium ion, which eventually leads
to the diene through a similar path to that observed by
[
7]
Julia.
Stereodefined conjugated dienes are of great importance
in organic synthesis[ as they constitute a common struc-
8]
[8a]
tural motif in natural products and are used as important
synthons in Diels–Alder reactions.[ A number of methods Experimental Section
8b]
for the preparation of conjugated dienes are available in the
General: NMR spectra were recorded with a DPX 300 instrument
[
9]
literature. Among these methods, the most widely em-
ployed are those based on the cross-coupling reaction of
1
13
at 300 MHz for H and at 75 MHz for C. IR spectra were mea-
sured with a FT 8300 Shimadzu spectrometer. Melting points were
alkenylmetals with haloalkenes in the presence of a transi- determined on a glass disk with an electrical bath (Reichert, Aus-
tion metal complex and olefin cross-metathesis reactions. tria) and are uncorrected. Dichloromethane was dried with P O
2
5
However, many of these are associated with significant and distilled before use. The cyclopropyl carbinols were prepared
by standard cyclopropanation procedures using diazomethane fol-
lowed by reduction with sodium borohydride.
limitations with regard to stability, easy accessibility and
toxicity of the catalysts used, stereoselectivity and yields of
dienes, and operational simplicity. However, the present General Procedure for the Preparation of Cyclopropyl Carbinols.
procedure is free from these disadvantages.
Preparation of Phenyl (2-phenylcyclopropyl)carbinol (Entry 1): A di-
Eur. J. Org. Chem. 2006, 3012–3015
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3013

B. C. Ranu, S. Banerjee
FULL PAPER
ethyl ether solution of diazomethane was added dropwise to a
stirred solution of 1,3-diphenylprop-2-ene-1-one (208 mg, 1 mmol)
and Pd(OAc) (10 mg) in diethyl ether (6 mL) at 0 °C and the reac-
2
127.7, 128.6 (2 C), 129.3, 131.9, 132.1, 132.5, 137.5, 147.3,
148.1 ppm. C17
81.40, H 5.43.
H14O (234.29): calcd. C 81.58, H 5.64; found C
tion mixture was kept as such for 10 h. It was then filtered through
a short column of silica gel to provide the crude cyclopropyl ketone
(
E,E)-1-(4-Benzyloxyphenyl)-4-phenyl-1,3-butadiene (Entry 9): White
–
1 1
crystals; m.p. 174–175 °C. IR (KBr): ν˜ = 1597, 1508, 1251 cm . H
NMR (300 MHz, CDCl ): δ = 5.09 (s, 2 H), 6.63 (d, J = 15.0 Hz,
H), 6.80–6.97 (m, 5 H), 7.34–7.43 (m, 11 H) ppm. 1 C NMR
75 MHz, CDCl ): δ = 69.9, 114.9 (2 C), 125.9, 126.1 (2 C), 127.1,
27.2, 127.3 (2 C), 127.5 (2 C), 127.8, 128.5 (4 C), 129.3, 130.3,
31.6, 132.2, 136.7, 137.4 ppm. C23 20O (312.40): calcd. C 88.43,
(222 mg, 100%). This crude compound was then stirred with
3
NaBH (58 mg, 1.5 mmol) in MeOH (10 mL) at 0 °C for 2 h. The
4
3
2
(
1
1
mixture was then quenched with water and diluted with diethyl
ether (10 mL). This mixture was filtered through a short plug of
silica gel and the filtrate was evaporated to provide the crude
alcohol, which was then purified by a short column chromatog-
raphy over silica gel (diethyl ether/hexane, 1:5) to furnish the de-
sired carbinol (212 mg, 95%) as a mixture of diastereoisomers. IR
3
H
H 6.45; found C 88.28, H 6.34.
–
1 1
(
0
neat): ν˜ = 3450, 1445, 1010 cm . H NMR (60 MHz, CCl
4
): δ = Acknowledgments
.84–1.00 (m, 2 H), 1.81–1.98 (m, 1 H), 2.47–2.56 (m, 1 H), 4.52–
4
.78 (m, 1 H), 6.99–7.89 (m, 10 H) ppm.
We are pleased to acknowledge financial support from CSIR, New
Delhi [grant no. 01(1936)/04], for this investigation. S.B. would like
to thank the CSIR for his fellowship.
This procedure was followed for the preparation of all carbinols
obtained as mixture of diastereoisomers) listed in Table 1.
(
General Procedure for Cyclopropyl Carbinol Rearrangement. Repre-
sentative Example of Conversion of Phenyl (2-Phenylcyclopropyl)-
[
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methanol into 1,4-Diphenyl-1,3-butadiene Catalyzed by In(OTf)
Entry 1): Phenyl (2-phenylcyclopropyl)methanol (224 mg, 1 mmol)
was sonicated in the presence of a catalytic amount (56 mg, 10 mol-
) of In(OTf) in dichloromethane (5 mL) in an ultrasonic cleaner
Julabo, Germany) for 25 min (TLC). The reaction mixture was
then diluted with diethyl ether (25 mL), washed with water and
dried (Na SO ). Evaporation of solvent gave a crude product,
3
5
5, 11149–11176; d) K. K. Chauhan, C. G. Frost, J. Chem.
(
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%
3
(
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2
4
which was purified by short column chromatography over silica gel
followed by recrystallization (diethyl ether/hexane, 1:2) to provide
pure 1,4-diphenyl-1,3-butadiene as a white solid (196 mg, 95%);
[
9]
1
m.p. 150–151 °C (ref. m.p. 152 °C) whose spectroscopic data ( H
1
3
[9]
and C NMR) were in good agreement with the reported values.
This procedure was followed for all reactions listed in Table 1. All
the products except those in Entries 6, 7, 8 and 9 are known and
were easily identified by comparison of their m.p., IR and NMR
1
13
[9–15]
(
H and C) spectra with those reported.
The melting points,
8
2
24–826; j) , Y.-C. Teo, K.-T. Tan, T.-P. Loh, Chem. Commun.
005, 1318–1319.
spectroscopic data (IR, H and 13C NMR) and elemental analysis
of the compounds that have not been reported in the literature are
provided below.
1
[3] a) G. Babu, P. T. Perumal, Aldrichimica Acta 2000, 33, 16; b) R.
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(
E,E)-4-Phenyl-1-(4-thiomethylphenyl)-1,3-butadiene (Entry 6): White
–
1 1
crystals; m.p. 138–140 °C. IR (KBr): ν˜ = 1590, 1474, 1436 cm . H
NMR (300 MHz, CDCl
6
5621–5624.
3
): δ = 2.47 (s, 3 H), 6.59–6.67 (m, 3 H), [4] a) B. C. Ranu, A. Hajra, U. Jana, J. Org. Chem. 2000, 65, 6270–
.86–6.95 (m, 3 H), 7.19–7.24 (m, 2 H), 7.30–7.36 (m, 3 H), 7.41–
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41, 531–533; c) B. C. Ranu, S. Samanta, A. Hajra, Synlett 2002,
13
7
3
.44 (m, 2 H) ppm. C NMR (75 MHz, CDCl ): δ = 15.6, 126.2
9
7
2
87–989; d) B. C. Ranu, A. Das, S. Samanta, Synlett 2002, 727–
30; e) B. C. Ranu, S. S. Dey, A. Hajra, Tetrahedron 2002, 58,
529–2532; f) B. C. Ranu, A. Hajra, S. S. Dey, U. Jana, Tetrahe-
(
1
8
2 C), 126.5 (2 C), 126.6 (2 C), 127.4, 128.4 (2 C), 128.5, 129.1,
32.0, 132.4, 134.2, 137.2, 137.7 ppm. C17
0.90, H 6.39; found C 80.71, H 6.19.
H16S (252.37): calcd. C
dron 2003, 59, 813–819; g) B. C. Ranu, S. Samanta, J. Org.
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(
E,E)-1-(4-Allyloxyphenyl)-4-phenyl-1,3-butadiene (Entry 7): White
–
1 1
crystals; m.p. 148–150 °C. IR (KBr): ν˜ = 1600, 1590, 1506 cm . H
NMR (300 MHz, CDCl ): δ = 4.55–4.57 (m, 2 H), 5.28–5.45 (m, 2
H), 6.00–6.09 (m, 1 H), 6.63 (d, J = 15 Hz, 4 H), 6.79–6.99 (m, 4
H), 7.22–7.45 (m, 5 H) ppm. 13C NMR (75 MHz, CDCl
): δ =
8.7, 114.7, 114.9 (2 C), 117.7, 126.2 (2 C), 127.2, 127.5 (2 C), 128.6
3
[
5] a) B. C. Ranu, T. Mandal, S. Samanta, Org. Lett. 2003, 5,
3
1
7
5
439–1441; b) B. C. Ranu, S. Samanta, J. Org. Chem. 2003, 68,
130–7132; c) B. C. Ranu, T. Mandal, J. Org. Chem. 2004, 69,
793–5795; d) B. C. Ranu, T. Mandal, Synlett 2004, 1239–1242;
6
(
(
2 C), 129.0, 129.5, 131.6, 132.4, 133.1, 137.5, 158.2 ppm. C19
262.35): calcd. C 86.99, H 6.92; found C 86.79, H 6.72.
18
H O
e) B. C. Ranu, A. Das, Tetrahedron Lett. 2004, 45, 6875–6877;
f) B. C. Ranu, S. Banerjee, A. Das, Tetrahedron Lett. 2004, 45,
(E,E)-1-(3,4-Dioxomethylenephenyl)-4-phenyl-1,3-butadiene
(En-
8
579–8581; g) B. C. Ranu, A. Das, Adv. Synth. Catal. 2005,
47, 712–714.
–
1
try 8): White crystals; m.p. 150 °C. IR (KBr): ν˜ = 1540, 1508 cm .
3
1
H NMR (300 MHz, CDCl
3
): δ = 5.94 (s, 2 H), 6.54–6.63 (m, 2
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7
13
(
(
m, 1 H), 7.29–7.33 (m, 2 H), 7.40–7.23 (m, 2 H) ppm. C NMR
75 MHz, CDCl ): δ = 101.1, 105.4, 108.4, 121.4, 126.3 (2 C), 127.4,
3
3014
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Eur. J. Org. Chem. 2006, 3012–3015

Rearrangement of Aryl-Substituted Cyclopropyl Carbinols
FULL PAPER
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Received: January 18, 2006
Published Online: April 26, 2006
Eur. J. Org. Chem. 2006, 3012–3015
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3015