Phthalazinone derivatives

H 1 N 1-10 C1 C2 1-10 5-20 3-20 C1 C2 5-7 A compound of the formula (I): wherein Rrepresents one or more optional substituents on the fused cyclohexene ring; Ris selected from H and halo; Ris selected from H and optionally substituted Calkyl; and Rand Rare independently selected from H, R, C(═O)OR, where R is optionally substituted Calkyl, optionally substituted Caryl or optionally substituted Cheterocyclyl; Rand Rtogether with the carbon atom to which they are attached may form an optionally substituted spiro-fused Ccarbocylic or heterocyclic ring.