Compounds for treating proliferative disorders

A compound represented by formula (Ia):

• or a tautomer, or a pharmaceutically acceptable salt thereof, wherein:
• Z1 are Z2 are independently O, S, Se, Te, Po, NR13, PR13, AsR13, SbR13 or BiR13;
• Z3 and Z4 are independently O, S, Se, Te, Po, N(R13)m, P(R13)m, As(R13)m, Sb(R13)m, or Bi(R13)m;
• provided that when one of Z1 or Z2 is S and the other is O or S, then Z3 and Z4 are not O or S, and provided that when Z1 and Z2 are both 0, then Z3 and Z4 are not both S;
• Y is an optionally substituted C1-C6 alkylene group;
• R″1 and R″2 are independently an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, or an optionally substituted heteroaryl;
• R3 and R4 are independently —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl or an optionally substituted heteroaryl;
• R5 and R6 are independently —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl or an optionally substituted heteroaryl;
• R13 for each occurrence is, independently, —H, —OR17, —NR19R20, —C(O)R17, —C(O)OR17, —OC(O)R17, —C(O)NR19R20, —NR18C(O)R17, —OP(O)(OR17)2, —SP(O)(OR17)2, —SR17, —S(O)pR17, —OS(O)pR17, —S(O)pOR17, —NR18S(O)pR17, or —S(O)pNR19R20, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl;
• R17 and R18, for each occurrence, are, independently, —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl;
• R19 and R20, for each occurrence, are independently —H, an optionally substituted alkyl, an optionally substituted alkenyl, an optionally substituted alkynyl, an optionally substituted cycloalkyl, an optionally substituted cycloalkenyl, an optionally substituted heterocyclyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl, or an optionally substituted heteraralkyl;
• or R19 and R20, taken together with the nitrogen to which they are attached, form an optionally substituted heterocyclyl or an optionally substituted heteroaryl;
• m is 0 or 1;
• and
• p is 1 or 2.