Synthesis of Benzoxazoles via Intramolecular Cyclization of ortho-Halobenzanilides using Copper Fluorapatite Catalyst

Abstract

An efficient method for the synthesis of benzoxazoles via intramolecular cyclization of ortho-haloanilides using heterogeneous copper fluorapatite catalyst is described. A variety of ortho-haloanilides (iodo-, bromo- and chloroanilides) were cyclized to the corresponding benzoxazoles, demonstrating the versatility of the ­reaction.

Key words

copper fluorapatite catalyst - ortho-haloanilides - intramolecular cyclization - heterogeneous catalyst

References and Notes

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18

Synthesis of Benzoxazoles; Typical Procedure: Catalyst Cu-FAP (100 mg) was added to a mixture of ortho-haloanilide (1 mmol), and K₂CO₃ (2 mmol) in DMF (4 mL) at 110 ˚C, and the mixture was stirred for 10-20 h. The progress of the reaction was monitored by TLC and on completion of the reaction, the mixture was centrifuged, the centrifugate was treated with ethyl acetate (20 mL) and washed with water. After removing the solvent, the crude material was purified by chromatography on silica gel (60-120 mesh) to afford 2-phenylbenzoxazole (Table  [³] , Entry 1)^¹¹a as a white solid. Mp 101-102 ˚C; ^¹H NMR (CDCl₃, 300 MHz): δ = 8.25-8.10 (m, 2 H), 7.76-7.70 (m, 1 H), 7.57-7.48 (m, 4 H), 7.33-7.27 (m, 2 H); EI-MS: m/z (%) = 195 [M⁺], 167 (28), 149 (17), 105 (27), 83 (59), 63 (52), 41 (42).