Process for the preparation of substituted 5-hydroxy-oxazoli din-4-one

A process for the synthesis of a compound of general formula II: II wherein: R2 and R3 are each independently hydrogen or C1-C4 alkyl; A is an aromatic or heteroaromatic ring system optionally substituted with one or more substituents as defined herein; and in which any ring nitrogen atom may be quaternised or oxidised; alternatively, any two substituents of the group A may combine to form a fused 5- or 6-membered saturated or partially saturated carbocyclic or heterocyclic ring in which any carbon or quaternised nitrogen atom may be substituted with any of the groups defined herein for A or in which a ring carbon atom may be oxidised; the process comprising cyclising a compound of general formula VII: VII wherein A, R2 and R3 are as defined for general formula II, R20 is hydrogen, benzyl or benzyl substituted with up to five substituents selected from halo, C1-C6 alkyl, O(C1-C6 alkyl) or nitro and R21 is C1-C8 alkyl, benzyl or benzyl substituted with up to five of the substituents mentioned above for R20.