Disclosed herein are pyrazolo[1,5-a]pyrimidine compounds of formula I, wherein the substituents are as defined within the specification, processes for their preparation, compositions comprising said compounds and uses thereof. Said compounds are useful as selective inhibitors of Janus kinases (JAK), in particular JAK2 and as such are useful for treating or lessening t the severity of a myeloproliferative disorder, or for treating or lessening the severity of a disease or condition selected from polycythemia vera, essential thrombocythemia, chronic idiopathic myelofibrosis, myeloid metaplasia with myelofibrosis, chronic myeloid leukaemia (CML), chronic myelomonocytic leukaemia, chronic eosinophilic leukaemia, hypereosinophilic syndrome, systematic mast cell disease or atypical CML or juvenile myelomonocytic leukemia.
