In a further interconversion process compounds of formula (1) wherein R9 is a carboxamido (--CONHR11) or a thiocarboxamido (--CSNHR11) group, may be prepared by reaction of a compound of formula (1) wherein R3 is a hydroxyl group with an isocyanate R11 NCO or an isothiocyanate R11 NCS, in a solvent, for example chloroform, in the presence of a base, for example diisopropylethylamine, at ambient te