3481
With more bulky naphthyl sulfonates the rearrangement is also regiospecific and the 2-isomers are
the exclusive products (Table 1, entries 4 and 5). This is in accordance with our recent results of ortho-
directed rearrangement of acyloxy benzenes and naphthalenes.7 4-Nitrophenyl p-toluenesulfonate does
not rearrange to the corresponding sulfone but hydrolysis of the sulfonate ester takes place in 40% yield.
This result indicates that electrophilic substitution does not occur, because the electron-withdrawing
group (4-nitro) deactivates the aromatic ring.
To demonstrate the efficiency of the methodology, when p-methylphenyl p-toluenesulfonate (Table 1,
entry 2) was mixed with the support, heated to about 250°C (the reaction mixture reaches this temperature
in microwave oven after 10 min) for 10 min in an oil bath, only the unchanged starting material was
isolated from the reaction medium. Furthermore, when the reaction mixture was heated at 250°C for a
longer period, some reaction product along with a tarry material was obtained owing to decomposition
of both product and starting material.
In conclusion, an AlCl3–ZnCl2 mixture supported on silica gel has been shown to be an efficient
medium for a regiospecific thia-Fries rearrangement of aryl sulfonates under microwave irradiation. This
method has the advantage of: (a) being a readily available medium; (b) the reaction is fast and solvent-
free; (c) a wide range of aryl or naphthyl sulfonates are rearranged by this medium; and, finally (d) the
ease of the work-up.
References
1. (a) Tobe, A., et al.; Japanese Patent, Jpn. Kokai Tokkyo Koho JP 63 63,612; Chem. Abstr. 1989, 111, 133770h; (b) Kato,
S.; Kitajima, T., Japanese Patent, Jpn. Kokai Tokkyo Koho JP 63 303,960; Chem. Abstr. 1989, 111, 96674g.
2. Nishijima, T., et al.; Japanese Patent, Jpn. Kokai Tokkyo Koho JP 63 09,573; Chem. Abstr. 1988, 109, 139306s.
3. Markley, L. D.; Tong, Y. C.; Wood, S. G. US Patent, US 4,349,568; Chem. Abstr. 1982, 97, 215735g.
4. (a) Martin, R. Org. Prep. Proc. Int. 1992, 24, 399; (b) Baliah, V.; Uma, M. Recl. Trav. Chim. Pays Bas 1961, 80, 139; (c)
Patwa, B. S.; Parikh, A. R. J. Inst. Chem. Calcutta 1976, 48, 116.
5. Venkatachalapathay, C.; Pitchumani, K. Tetrahedron 1997, 53, 17 171, and references cited therein.
6. Varma, R. S. In Microwaves: Theory and Application in Material Processing IV; Clark, D. E.; Sutton, W. H.; Lewis, D. A.,
Eds. Microwave-assisted reactions under solvent-free ‘dry’ conditions. American Ceramic Society, Ceramic Transactions,
1997; Vol. 80, pp. 357–365.
7. Matloubi Moghaddam, F.; Ghaffarzadeh, M.; Abdi-Oskoui, S. H. J. Chem. Res. (S) 1999, (9), 575.
8. (a) Matloubi Moghaddam, F.; Emami, R. Synth. Commun. 1997, 27, 4073; (b) Matloubi Moghaddam, F.; Ghaffarzadeh, M.
Tetrahedron Lett. 1996, 37, 1855; (c) Matloubi Moghaddam, F.; Sharifi, A.; Saidi, M. R. J. Chem. Res. (S) 1996, 388.
9. The support was prepared as described in Ref. 7 and the minimum amount of supported reagent to substrate was found to be
3:1 (w/w) after performing several optimization experiments. General procedure for thia-Fries rearrangement of sulfonates:
To a solution of arylsulfonate (1 g) in 5 ml of anhydrous chloroform, 3 g of support was added. After evaporation of the
solvent, the mixture was subjected to microwave irradiation for the given times (Table 1). The cooled reaction mixture was
extracted with ethyl acetate (3×50 ml) and the solvent was evaporated under vacuum. The product was isolated by column
chromatography of the crude reaction mixture on silica gel (eluent: dichloromethane:petroleum ether).
10. The microwave oven used for this work was an AEG (650 Watt) at 2450 MHz (100% power) which was modified to a
focused monomode system in our laboratory.
11. Goghari, M. H.; Parikh, A. R. J. Inst. Chem. Calcutta 1976, 48, 73.
12. (a) Aleykutty, A. A.; Baliah, V. J. Indian Chem. Soc. 1954, 31, 513; (b) Balasubramanian, V.; Baliah, V. ibid. 1960, 37,
722; (c) Balasubramanian, V.; Baliah, V. ibid. 1959, 36, 391.