This phase III trial compares the effect of adding pirtobrutinib to the usual treatment with rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP) to R-CHOP alone for the treatment of Richter transformation, which is when chronic lymphocytic leukemia or small lymphocytic lymphoma turns into large B-cell lymphoma, a more aggressive (faster-growing) form of lymphoma. Pirtobrutinib may stop the growth of cancer cells by blocking some of the enzymes needed for cell growth. Rituximab is a monoclonal antibody. It binds to a protein called CD20, which is found on B cells (a type of white blood cell) and some types of cancer cells. This may help the immune system kill cancer cells. Cyclophosphamide is in a class of medications called alkylating agents. It works by damaging the cell's DNA and may kill cancer cells. It may also lower the body's immune response. Doxorubicin is in a class of medications called anthracyclines. Doxorubicin damages the cell's DNA and may kill cancer cells. It also blocks a certain enzyme needed for cell division and DNA repair. Vincristine is in a class of medications called vinca alkaloids. It works by stopping cancer cells from growing and dividing and may kill them. Prednisone is in a class of medications called corticosteroids. It is used to reduce inflammation and lower the body's immune response to help lessen the side effects of chemotherapy drugs. Adding pirtobrutinib to R-CHOP may kill more cancer cells than R-CHOP alone in patients with Richter transformation.