The present invention provides novel compounds of Formula (I), and pharmaceutically acceptable salts, solvates, hydrates, polymorphs, co-crystals, tautomers, stereoisomers, isotopically labeled derivatives, prodrugs, and compositions thereof. Also provided are methods and kits involving the inventive compounds or compositions for treating or preventing proliferative diseases (e.g., cancers (e.g., lung cancer, breast cancer, leukemia, lymphoma, melanoma, multiple myeloma, Ewing's sarcoma, osteosarcoma, brain cancer, neuroblastoma), benign neoplasms, angiogenesis, inflammatory diseases, autoinflammatory diseases, and autoimmune diseases) in a subject. Treatment of a subject with a proliferative disease using a compound or composition of the invention may inhibit the aberrant activity of a kinase (e.g. a protein kinase (e.g. a cyclin-dependent kinase (CDK) (e.g. CDK7, CDK12, or CDK13) or a lipid kinase such as a phosphatidylinositol-5-phosphate 4-kinase (PIP4K) (e.g., PI5P4Kα, PI5P4Kβ, or PI5P4Kγ)) in the subject.