654
D. Sarkar, R. V. Venkateswaran
LETTER
cases the rearranged products were obtained in very high
yields at room temperature. In the case of the allyl ether
(entry 6), a minor amount of an isomer was also isolated
and allyl ether (entry 10), the rearranged product under-
went subsequent cyclisation resulting in the formation of
a dihydrobenzofuran. The products were characterised
from their spectroscpic data and comparison with data re-
ported in literature.12–19 The structure of the novel benzo-
furan (entry 10) was also established from analytical and
spectroscopic studies.20 The ready availability of the cata-
lyst and the simple and mild reaction conditions attest to
the viability of this procedure. Substrates possessing an
electron-withdrawing substituent (Scheme 1 and entry 9)
react in lower yields (the presence of strategically placed
electron-donating groups in the aromatic moiety affecting
the reaction rate in catalysed Claisen rearrangement has
precedent9).
References and Notes
(1) Claisen, L. Chem. Ber. 1912, 45, 3157.
(2) For reviews, see: (a) Lutz, R. P. Chem. Rev. 1984, 84, 205.
(b) Castro, A. M. M. Chem. Rev. 2004, 104, 2939.
(3) (a) Brtyusova, L. Ya.; Ioffe, M. L. J. Gen. Chem.(U.S.S.R.)
1941, 11, 722; Chem. Abstr. 1942, 36, 430. (b) Cairns, N.;
Harwood, L. M.; Astles, D. P. J. Chem. Soc., Chem.
Commun. 1986, 750.
(4) (a) Svanholm, U.; Parker, V. D. J. Chem. Soc., Chem.
Commun. 1972, 645. (b) Harwood, L. M. J. Chem. Soc.,
Chem. Commun. 1983, 530. (c) Harwood, L. M. J. Chem.
Soc., Perkin Trans. 2 1984, 2577.
(5) (a) Borgulya, J.; Madeja, R.; Fahrni, P.; Hansen, H.-J.;
Schmid, H.; Barner, R. Helv. Chim. Acta 1973, 56, 14.
(b) Cairns, N.; Harwood, L. M.; Astles, D. P.; Alex, O. J.
Chem. Soc., Chem. Commun. 1986, 182. (c) Ito, F.; Fusegi,
K.; Kumamoto, T.; Ishikawa, T. Synthesis 2007, 1785.
(6) Kim, K. M.; Kim, H. R.; Chung, K. H.; Song, J. H.; Ryu, E.
K. Synth. Commun. 1994, 24, 1859.
(7) (a) Sonnenberg, F. M. J. Org. Chem. 1970, 35, 3166.
(b) Wipf, P.; Ribe, S. Org. Lett. 2001, 3, 1503.
(8) Hayashi, T.; Goto, M. Nippon Kagaku Kaishi 1978, 1007;
Chem. Abstr. 1978, 89: 128852.
(9) Narasaka, K.; Bald, E.; Mukaiyama, T. Chem. Lett. 1975,
1041.
(10) Sharma, G. V. M.; Ilangovan, A.; Sreenivas, P.;
Mahalingam, A. K. Synlett 2000, 615.
In summary, we have described a very mild and high-
yielding procedure for effecting the aromatic Claisen re-
arrangement employing the readily available tin(IV) chlo-
ride as catalyst. It is expected that this procedure will
serve as a very useful alternative to the other conditions
for effecting this transformation.
(11) The only previous example of a tin(IV) chloride catalysed
rearrangement of a deuterium-labelled allyl tolyl ether
involved heating in decalin, see: Feoktistov, V. M.; Bunina-
Krivorukova, L. I. Zh. Org. Khim. 1978, 14, 807.
(12) Wipf, P.; Rodriguez, S. Adv. Synth. Catal. 2002, 344, 434.
(13) Pincock, L. A.; Pincock, A. J.; Stefanova, R. J. Am. Chem.
Soc. 2002, 124, 9768.
(14) Krohn, K.; Bernhard, S. Synthesis 1996, 699.
(15) Lecornué, F.; Olliver, J. Synth. Lett. 2004, 1613.
(16) Benbow, W. J.; Rouse, K.-R. J. Org. Chem. 2001, 66, 4965.
(17) Tsang, Y. K.; Brimble, A. M.; Bremner, B. J. Org. Lett.
2003, 5, 4425.
In a typical experiment, the allyl aryl ether (1 mmol) in dry CH2Cl2
(2 mL) was treated with SnCl4 (1.0 M solution in CH2Cl2, 1.2
mmol), added via syringe at 0 °C and allowed to attain r.t. and
stirred for the durations indicated in Table 1 under a nitrogen atmo-
sphere. After the reaction was complete (as monitored by TLC), the
reaction mixture was cooled (0 °C), quenched with cold H2O and
extracted with CH2Cl2. The organic extracts were washed with sat.
brine and dried (Na2SO4). Evaporation of the solvent followed by
chromatography of the residue over silica gel furnished the desired
compound. An experiment with substrate in entry 2 employing less
than 1 mol equiv of SnCl4 resulted in substantially reduced rear-
rangement even after increased reaction time.
(18) Ollevier, T.; Mwene-Mbeja, M. T. Tetrahedron Lett. 2006,
47, 4051.
(19) Quefflec, C.; Bailly, F.; Cotelle, P. Synthesis 2006, 768.
(20) 7-Methoxy-2,5-dimethyl-dihydrobenzofuran (Entry 10)
Obtained as a colourless solid. Crystallised from Et2O-PE,
mp43-44 °C. 1H NMR (300 MHz, CDCl3): d = 1.51 (d,
J = 11.5 Hz, 3 H), 2.28 (s, 3 H), 3.02 (dd, A of ABX,
JAB = 13.8 Hz, 1 H), 3.04 (dd, B of ABX, JBA = 13.8 Hz, 1
H), 3.87 (s, 3 H), 4.40 (sext, X of ABX, JAX = JBX = 6.6 Hz,1
H), 6.58 (s, 1 H), 6.60 (s, 1 H). 13C NMR (75 MHz, CDCl3):
d = 21.2, 24.9, 41.2, 56.0, 57.7, 110.3, 123.6, 123.8, 128.8,
141.6, 146.2. HRMS (ES+ve): m/z calcd for C11H14O2 [M +
Na]+: 201.0892; found: 201.0889.
Acknowledgment
We acknowledge financial support from the Department of Science
and Technology, Govt. of India. D.S. thanks the Council of Scienti-
fic & Industrial Research, New Delhi for a Research Fellowship.
Synlett 2008, No. 5, 653–654 © Thieme Stuttgart · New York