| http://www.w3.org/ns/prov#value | - (i) a compound of the formula I wherein Y is a hydroxy radical and R1, R2, R3, R4, R5, R6 and X have any of the meanings given above, is reacted with a halogenating agent, for example diethylamino sulphur trifluoride, thionyl chloride, phosphoryl chloride, thionyl bromide or phosphoryl bromide, to form a corresponding compound of the invention wherein Y is a halogen atom; or
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