Clofarabine and Cyclophosphamide in Treating Patients With Relapsed or Refractory Acute Leukemia, Chronic Myelogenous Leukemia, or Myeloproliferative Disorders

DISEASE CHARACTERISTICS: * Histologically confirmed leukemia or myeloproliferative disorders, including 1 of the following: * Acute myeloid leukemia (AML) of any subtype * Treatment-related AML OR AML evolving from myeloproliferative disorders (MPD) or transformed from myelodysplastic syndrome * Acute lymphocytic leukemia * Acute progranulocytic leukemia * Must not be eligible for arsenic or retinoic acid therapy * Chronic myelogenous leukemia in accelerated phase or blast crisis * High-risk MPD, including any of the following: * Myelofibrosis * Chronic myelomonocytic leukemia with 5%-19% blasts * Relapsed or refractory juvenile myelomonocytic leukemia * Relapsed and/or refractory disease with progressive disease since last therapy * No more than 3 prior induction regimens with cytotoxic agents for adults * Must be in second relapse for patients \< 21 years of age PATIENT CHARACTERISTICS: * ECOG performance status 0-2 (for adults) OR Lansky 50-100% (for pediatric patients) * Bilirubin ≤ 1.5 mg/dL (may be elevated due to hemolysis in adult patients) * AST and ALT ≤ 5 times upper limit of normal * Creatinine ≤ 2.0 mg/dL (for adults) * Normal renal function (for pediatric patients) * Cardiac function normal as measured by MUGA scan or echocardiogram * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective barrier contraception during and for at least 6 months after completion of study treatment * HIV nega…