Compound of formula CHEM wherein Ar represents a 4-OP substituted phenyl or naphtyl (P being a protecting group) which may be further substituted, and Ar min a possibly substituted phenyl or naphtyl rest, R is hydrogen, an alkali metal or a carbonyl residue, and X represents the atoms to complete a 2,3-dihydrobenz(d) isothiazole-1,1-dioxide or a 2,3-dihydronaphto (1,8-d,e) 1,2-thiazine-1,1-dioxide ring, which are useful intermediates in the synthesis of certain derivates of formula (I) wherein Ar represents a possibly further substituted 4-OH phenyl or naphtyl rest. The product produced are useful, for example, as photographic optical filter agents and filter agent precursors.
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