3-hydroxyazaecyclobutane hydrochloride is an azaecyclobutane compound that is an important intermediate in the synthesis of Brectinib, which is obtained through a multi-step reaction. Brectinib was approved by the European Union. The monotherapy or in combination with methotrexate for the treatment of adult patients with moderate to severe active rheumatoid arthritis with inadequate or intolerant relief from one or more antirheumatic drugs. It is also the first JAK inhibitor approved in the European Union for the treatment of rheumatoid arthritis.