The present disclosure 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 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 disorders, in particular their use in diseases or disorders associated as bromodomain inhibitors. The present disclosure also provides preparation of compounds and pharmaceutical formulations comprising at least one of bicyclic heterocyclic derivatives of formula (I), together with a pharmaceutically acceptable carrier, diluent, or excipient.