A compound of the formula (I) ** Formula ** characterized in that X represents a carbon atom, and R1a and R2a, together, form a bond； or X represents a carbon atom, R1a and R2a, together, form a bond, and R1 and R2, together, form the ** Formula ** fragment in which the asterisk indicates the point of attachment of R 2； or X represents a carbon atom, R1a represents hydrogen or (C1-4) alkoxy, and R2a represents hydrogen； or X represents a carbon atom, R1 and R1a, together, form a 3H-benzofuran-2,2-diyl group, and R2 and R2 represent both hydrogen； or X represents a nitrogen atom, R1a is absent, and R2 and R2a both represent hydrogen or R2 and R2a, together, form a carbonyl group； and R1 and R2, if not indicated otherwise, independently represent hydrogen； (C1-5) alkyl； aryl, which is substituted, or independently mono-, di- or trisubstituted in which the substituents are independently selected from the group consisting of (C1-4) alkyl, (C1-4) alkoxy, halogen, trifluoromethyl, trifluoromethoxy, cyano and cycloalkyl (C3-6)； or heteroaryl, which is unsubstituted, or independently mono-, di- or trisubstituted in which the substituents are independently selected from the group consisting of (C1-4) alkyl, (C1-4) alkoxy, halogen, cyano, trifluoromethyl and trifluoromethoxy ； with the proviso that in the case where R2 represents aryl or heteroaryl, R1 cannot represent aryl or heteroaryl, the aryl and heteroaryl being independently substituted or substituted as defined above.Un compuesto de la fórmula (I)**Fórmula** caracterizado porque X representa un átomo de carbono, y R1a y R2a, conjuntamente, forman un enlace； o X representa un átomo de carbono, R1a y R2a, conjuntamente, forman un enlace, y R1 y R2, conjuntamente, forman el fragmento**Fórmula**en el que el asterisco indica el punto de unión de R 2； o X representa un átomo de carbono, R1a representa hidrógeno o alcoxi (C1-4), y R2a representa hidrógeno； o X representa un átomo de carbono, R1 y R1a, conjuntamente, forman u
