Disclosed are compounds of Formula 1, or pharmaceutically acceptable salts thereof, wherein R1, R2, R3, and R4 are defined in the specification. This disclosure also relates to materials and methods for preparing compounds of Formula 1, to pharmaceutical compositions which contain them, and to their use for treating Type I hypersensitivity reactions, autoimmune diseases, inflammatory disorders, cancer, non-malignant proliferative disorders, and other conditions associated with BTK.