The acylation of 4-(5-methyl-3-phenylisoxazol-4-yl)benzenesulfonamide, valdecoxib (I), with propionic anhydride (II) by means of TEA and DMAP in THF gives N-[4-(5-methyl-3-phenylisoxazol-4-yl)phenylsulfonyl]propionamide (III), which is then treated with NaOH in ethanol.
Deoxybenzoin (I) is converted to the corresponding oxime (II) by treatment with NH2OH稨Cl under basic conditions either with sodium acetate in aqueous ethanol or in toluene in presence of potassium hydroxide in absolute ethanol. Deprotonation of the oxime under nitrogen with 2eq of butyllithium in THF followed by cyclization in ethyl acetate or acetic anhydride affords isoxazoline (III). Finally, treatment of (III) with cold chlorosulfonic acid followed by reaction of the intermediate sulfonyl chloride with aqueous ammonia affords the desired product.