The present invention provides bicyclic heterocyclic derivatives of formula (I), which may be therapeutically useful, more particularly as bromodomain inhibitors; (I), in which R1, R2, R3, R4, L1, L2, Cy1, Cy2, X, n and dotted line are have the same meaning given in the specification, and pharmaceutically acceptable salts or pharmaceutically acceptable stereoisomers thereof that are useful in the treatment and prevention of diseases or disorder, in particular their use in diseases or disorder associated as bromodomain inhibitors. The present invention also provides preparation of the compounds and pharmaceutical formulations comprising at least one of bicyclic heterocyclic derivatives of formula (I), together with a pharmaceutically acceptable carrier, diluent or excipient therefor.