Synlett 2010(5): 777-781  
DOI: 10.1055/s-0029-1219342
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Gold(III)-Catalyzed Synthesis of Isoxazoles by Cycloisomerization of α,β-Acetylenic Oximes

C. Praveen, A. Kalyanasundaram, P. T. Perumal*
Organic Chemistry Division, Central Leather Research Institute, Adyar, Chennai 600 020, India
Fax: +91(44)24911589; e-Mail: ptperumal@gmail.com;
Further Information

Publication History

Received 30 November 2009
Publication Date:
19 January 2010 (online)

Abstract

Cycloisomerization of α,β-acetylenic oximes leading to substituted isoxazoles was achieved using AuCl3 as catalyst, under moderate reaction conditions. The reaction can be applied to various acetylenic oximes and gives good to excellent yields. The methodology is amenable for the selective synthesis of 3-substituted, 5-substituted or 3,5-disubstituted isoxazoles by simply altering the substituents on the acetylenic oximes.

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Synthesis of 3-Methyl-5-trimethylsilylisoxazole (3); Typical Procedure: To a solution of oxime 2n (500 mg, 3.22 mmol) in anhydrous CH2Cl2, was added AuCl3 (9.76 mg, 0.0321 mmol) under an N2 atmosphere and the solution was stirred for the specified time (Table  [²] ) at 30 ˚C. After completion of the reaction (as indicated by TLC), the reaction mixture was concentrated under reduced pressure and purified by column chromatography over silica gel (100-200 mesh) to afford pure product, 3-methyl-5-trimethylsilylisoxazole (3n) as a yellow oil; IR (neat): 3302, 2912, 1604, 1419, 1338, 1085, 885, 757 cm. ¹H NMR (500 MHz, CDCl3): δ = 0.29 [s, 9 H, Si(CH 3)3], 2.29 (s, 3 H, CH3), 6.24 (s, 1 H, isoxazolinyl-H). ¹³C NMR (125 MHz, CDCl3): δ = -1.8, 10.8, 113.5, 157.7, 177.8. MS (EI): m/z = 172 [M]+. Anal. Calcd for C7H13NOSi: C, 54.15; H, 8.44; N, 9.02. Found: C, 53.95; H, 8.47; N, 9.15.