InCl3-Zn. A novel reduction system for the deoxygenative coupling of carbonyl compounds to olefins

Article abstract of DOI:10.1055/s-2001-12326

A simple and inexpensive procedure for the deoxygenative homo-coupling and cross-coupling of carbonyl compounds with InCl₃-Zn system in dry acetonitrile at ambient pressure is achieved. The procedure gives excellent yields of E-olefinic products.

Full text of DOI:10.1055/s-2001-12326

LETTER
515
InCl3-Zn. A Novel Reduction System for the Deoxygenative Coupling of
Carbonyl Compounds to Olefins
Dhiren C. Barman, Ashim J. Thakur, Dipak Prajapati, Jagir S. Sandhu*
Department of Organic Chemistry, Regional Research Laboratory, Jorhat-785 006, Assam, India
Fax +91 0376 370011; E mail: drrljt@csir.res.in
Received 21 November 2000
Abstract: A simple and inexpensive procedure for the deoxygen-
ative homo-coupling and cross-coupling of carbonyl compounds
with InCl3-Zn system in dry acetonitrile at ambient pressure is
achieved. The procedure gives excellent yields of E-olefinic prod-
ucts.
Key words: indium, reductive coupling, olefins, carbonyl com-
pounds, stilbenes
Scheme 1
mmol) in dry acetonitrile (30 mL), was added benzalde-
hyde (650 mg, 6 mmol) dropwise. Then the resulted mix-
ture was allowed to stir for 5 min and subjected to reflux
for 8 h. After completion (vide TLC), the solvent was
evaporated and the residue was extracted with chloroform
(3 30 mL). The organic layer was than washed with
NaHCO3 solution (20%) and dried over anhydrous sodi-
um sulfate. Removal of solvent on a rotary evaporator and
purification of the residue by column chromatography on
silica gel gave the corresponding trans-stilbene 2a, mp
124 °C (lit.13 mp 124 °C) in 93% yield with no evidence
for the formation of side products. -Carotene, a food col-
oring compound and precursor of vitamin A, can also be
prepared in high yield from retinal (Table, entry 2f) using
this new system. Similar treatment of other aldehydes
gave the corresponding olefins 2 in 60-93% yields (Ta-
ble), again with no evidence for the formation of side
products. When acetophenone was used in place of benz-
aldehyde and refluxed for 9 h, it gave only 60% yield of
corresponding olefin. Increasing the reaction time further
had no significant effect on the yield and resulted in minor
decomposition. This novel InCl3-Zn system also catalyzes
the cross-coupling reaction of aldehydes in presence of a
ketone. The reactions were carried out with a ratio (1:2) of
the two carbonyl compounds and the corresponding cross-
coupled products were obtained in high yields along with
the homo-coupled products (Scheme 2). All the com-
Indium mediated reactions have recently emerged as a
useful tool in organic synthesis.1 In particular, it was re-
cently found that the low reactivity of trivalent organoin-
dium reagents can be easily increased by the complex
formation with organolithium compounds.2 The tetraor-
gano indates thus prepared are sufficiently reactive to take
part in reactions at ambient temperature.2a Allylic indates
react with imides and nitriles regioselectively at the -car-
bon to give homoallylamines.2b Organoindium com-
pounds derived from dibromo substituted active
methylene compounds, such as dibromo malononitrile,
and indium metal react with alkenes and carbonyl com-
pounds to give the cyclopropanes and oxiranes, depending
on the nature of the reagents and substrates.3 Our interest
in the catalytic carbon-carbon bond formation and indium
based reagents4 prompted us to investigate the use of indi-
um in the reductive coupling of carbonyl compounds. The
deoxygenative coupling of aldehydes and ketones to give
alkenes on treatment with low valent titanium was first
reported5 in 1974 and it still constitutes an important
method for the formation of carbon-carbon bonds. Later
several reagents6 have been reported for this coupling
which include magnesium/mercury,7 NbCl5/NaAlH4,7
zinc-copper couple,8 LiAlH4,9 dicyclopentadienyl titani-
umdichloride, trimethyl aluminium10 or Grignard re-
agents.11 But these methods have their merits as well as
limitations. To our knowledge, the use of indium for this
reaction has not so far been employed. However, one ex-
ample of indium in t-BuOH under sonication was
reported12 for the homo-coupling of aromatic aldehydes to
generate pinacol type of products and not the olefins. We
report herein a novel system consisting of InCl3-Zn for the
deoxygenative coupling of carbonyl compounds under
thermal conditions to generate directly alkenes. The reac-
tion proceeds smoothly at ambient pressure to yield the
corresponding olefins in high yields.
1
pounds obtained were characterized by infrared and H
NMR spectroscopy and finally by comparison with au-
thentic samples.
In conclusion, this new InCl3-Zn reduction system compa-
rable to McMurry’s reagent14 for the carbon-carbon bond
formation shows unique selectivity and constitute a useful
alternatilve to the commonly accepted procedure for the
synthesis of E-olefins of potentially high synthetic utility.
Also this simple and easily reproducible technique affords
various homo-coupled and cross-coupled olefins in excel-
lent yields and without the formation of any undesirable
side products, than the classical homogeneous reactions.
In a typical procedure, to a well stirred suspension of zinc
powder (1 g, 16 mmol) and anhydrous InCl3 (1.8 g, 8
Synlett 2001 No. 4, 515–516 ISSN 0936-5214 © Thieme Stuttgart · New York

516
D. C. Barman et al.
LETTER
Acknowledgement
One of us (AJT) thanks Council of Scientific Industrial Research
(CSIR), New Delhi for the award of a Junior Research Fellowship
to him.
References and Notes
(1) For a recent report on indium see: Araki, S., Jin, S. J.,
Butsugan, Y., J. Chem. Soc., Perkin Trans 1. 1995, 549;
Araki, S., Yamada, M. and Butsugan, Y., Bull. Chem. Soc.
Jpn. 1994, 67, 1126 and references cited therein. For a recent
review on indium catalyzed reactions see: Li, C. J., Chan, T.
H., Tetrahedron 1999, 55, 11149-11176.
(2) a) Jin, S. J., Araki, S. and Butsugan, Y., Bull. Chem. Soc.,
Japan 1993, 66, 1528; b) Araki, S., Shimizu, T., Jin, S. J. and
Butsugan, Y., J. Chem. Soc., Chem. Commun. 1991, 824.
(3) Araki, S., Butsugan, Y., J. Chem. Soc., Chem. Commun. 1989,
1286; Araki, S., Hirashita, T., Shimizu, K., Ikeda, T. and
Butsugan, Y., Tetrahedron 1996, 52, 2803.
Scheme 2
Table InCl3-Zn mediated reductive coupling of carbonyl com-
(4) Gadhwal, S., and Sandhu, J. S., J. Chem. Soc., Perkin Trans 1.
2000, 2827; Prajapati, D., Laskar, D. D. and Sandhu, J. S.,
Tetrahedron Lett. 2000, (in press); Boruah, A., Baruah, B.,
Prajapati, D., Sandhu, J. S. and Ghosh, A. C., Tetrahedron
Lett. 1996, 37, 4203.
pounds.
(5) Tyrlik, S., Wolochowicz, I., Bull. Soc. Chim., Fr. 1973, 2147.
(6) Lenoir, D., Synthesis 1989, 883
(7) Corey, E. J., Danheiser, Chandrasekaran, S., J. Org. Chem.
1976, 41, 260.
(8) Ghiringhelli, D., Tetrahedron Lett. 1983, 24, 287.
(9) Ishida, A., Mukaiyama, T., Chem. Lett. 1976, 1127.
(10) Brown-Wenstey, K. A., Buchwald, S. L., Cannizzo, L.,
Clawson, L., Ho, S., Meinhardt, D., Stille, J. R., Straus, D.,
Grubbs, R. H., Pure and Appl. Chem. 1983, 55, 173.
(11) Sato, F., J. Organomet. Chem. 1985, 285, 53.
(12) Lim, H. J., Keum, G., Kang, S. B., Chung, B. Y., Kim, Y.,
Tetrahedron Lett. 1998, 39, 4367.
(13) Devlin, C. J., Walker, B. J., J. Chem. Soc., Perkin Trans 1
1972, 1249.
(14) McMurry, J. E., Chem. Rev. 1989, 89, 1513.
Article Identifier:
1437-2096,E;2001,0,04,0515,0516,ftx,en;L21300ST.pdf
aProducts were identified by the comparison of IR and NMR spectra
and melting points with those of authentic samples. bYields refer to
c
1
the yield of pure isolated products. The E/Z ratio measured by H
NMR.
Synlett 2001, No. 4, 515–516 ISSN 0936-5214 © Thieme Stuttgart · New York