From o-Hydroxybenzoyl Oximes and Related Compounds

Cyclization conditions also seem to be of paramount importance in determining the products from the ring closure of o-hydroxy-a-acylchalcone (10).15 Treatment of 10 with hydroxylamine hydrochloride in pyridine furnishes the oxime (11 X = NOH) of the o-hydroxybenzoylisoxazoline (11 X = O), the product from the action of hydroxylamine hydrochloride and sodium acetate on the chalcone. In contrast, with ethanolic hydroxylamine hydrochloride, 10 yields only the indoxazene (12 R = Ac, Ar = Ph). 

The structures of the by-products from the action of hydroxylamine on 6- and 7-methylcoumarin have now been confirmed as 5- and 6-methyl-indoxazene-3-acetic acid, respectively.1,20 Careful investigation shows that with a large excess of hydroxylamine coumarins form 1 3 adducts which 

The reaction of thionyl chloride with salicylhydroxamic acids (22 R2 = H) has been developed as a general synthetic method for 3-hydroxy-indoxazenes.1,23 An improvement of this two-stage process is claimed by treating the hydroxamic acids with carbonyl diimidazole in boiling tetra-hydrofuran followed by acidification.24 

The action of cold thionyl chloride on salicylhydroxamic acids, and on o-hydroxyaldoximes and -ketoximes, is a versatile synthetic route to 3-hydroxy-, 3-unsubstituted, and 3-alkylindoxazenes.26 

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