A compound having the formula: wherein X is oxygen or NR x; R x is hydrogen; a is a double bond, b is a single bond, and R 1, R 2, and R 3, are, independently, hydrogen, C 1-6 aliphatic, heteroC 1-6 aliphatic, hydroxy, thio, heterocyclic, C 3-20 aryl, heteroaryl, acyl, amido, imido, sulfinyl, sulfonyl, cyano, azido, halo; optionally substituted with oxo, thiooxo, imino, C 1-6 aliphatic, C 3-6 carbocyclic, hydroxy, C 1-8 aliphaticoxy, C 3-20 aryloxy, thio, C 1-8 aliphaticthioxy, C 3-20 arylthioxy, heteroC 1-6 aliphatic, heterocyclic, C 3-20 aryl, C 3-20 arylC 1-6 aliphatic, heteroaryl, heteroarylC 1-6 aliphatic, acyl, acyloxy, amido, imido, sulfinyl, sulfonyl, amino, C 1-6 aliphaticamino, C 1-6 dialiphaticamino, C 1-6 trialiphaticamino, C 3-20 arylamino, C 3-20 diarylamino, carboxaldehyde, cyano, isocyano, azido, hydrazino, nitro, or halo; or R 1 and R 2 are joined to form a 5- to 6-membered optionally substituted carbocyclic, optionally substituted heterocyclic, optionally substituted aryl or optionally substituted heteroaryl ring; or R 2 and R 3 are joined to form a 5- to 6-membered optionally substituted carbocyclic, optionally substituted heterocyclic, optionally substituted aryl or optionally substituted heteroaryl ring; Ar is a group selected from C 3-20 aryl or heteroaryl, each group optionally substituted with C 1-6 aliphatic, heteroC 1-6 aliphatic, C 3-6 carbocyclic, hydroxy, C 1-8 aliphaticoxy, C 3-20 aryloxy, thio, C 1-8 aliphaticthioxy, C 3-20 arylthioxy, heteroC 1-6 aliphatic, heterocyclic, C 3-20 aryl, C 3-20 arylC 1-6 aliphatic, heteroaryl, heteroarylC 1-6 aliphatic, acyl, acyloxy, amido, imido, sulfinyl, sulfonyl, amino, C 1-6 aliphaticamino, C 1-6 dialiphaticamino, C 1-6 trialiphaticamino, C 3-20 arylamino, C 3-20 diarylamino, carboxaldehyde, cyano, isocyano, azido, hydrazino, nitro, or halo; wherein said heteroaliphatic is an aliphatic moiety wherein one or more carbon atoms is replaced with one or more of oxygen, sulphur, nitrogen, phosphorus or silicon; said heter o cyclic is a non-aromatic, partially unsaturated or fully saturated 3 to 10 membered ring system having from one to three heteroatoms selected from oxygen, sulphur and nitrogen; said heteroaryl is a stable aromatic mono or polycyclic ring system having 3-20 ring atoms of which 1 to 3 ring atoms are selected from sulphur, oxygen or nitrogen; and pharmaceutically acceptable salts, configurational isomers, or tautomers, thereof for use in treating a tumor associated with a EGFR and/or KRAS mutation. X is oxygen or NR x; R x is hydrogen; a is a double bond, b is a single bond, and R 1, R 2, and R 3, are, independently, hydrogen, C 1-6 aliphatic, heteroC 1-6 aliphatic, hydroxy, thio, heterocyclic, C 3-20 aryl, heteroaryl, acyl, amido, imido, sulfinyl, sulfonyl, cyano, azido, halo; optionally substituted with oxo, thiooxo, imino, C 1-6 aliphatic, C 3-6 carbocyclic, hydroxy, C 1-8 aliphaticoxy, C 3-20 aryloxy, thio, C 1-8 aliphaticthioxy, C 3-20 arylthioxy, heteroC 1-6 aliphatic, heterocyclic, C 3-20 aryl, C 3-20 arylC 1-6 aliphatic, heteroaryl, heteroarylC 1-6 aliphatic, acyl, acyloxy, amido, imido, sulfinyl, sulfonyl, amino, C 1-6 aliphaticamino, C 1-6 dialiphaticamino, C 1-6 trialiphaticamino, C 3-20 arylamino, C 3-20 diarylamino, carboxaldehyde, cyano, isocyano, azido, hydrazino, nitro, or halo; or R 1 and R 2 are joined to form a 5- to 6-membered optionally substituted carbocyclic, optionally substituted heterocyclic, optionally substituted aryl or optionally substituted heteroaryl ring; or R 2 and R 3 are joined to form a 5- to 6-membered optionally substituted carbocyclic, optionally substituted heterocyclic, optionally substituted aryl or optionally substituted heteroaryl ring; Ar is a group selected from C 3-20 aryl or heteroaryl, each group optionally substituted with C 1-6 aliphatic, heteroC 1-6 aliphatic, C 3-6 carbocyclic, hydroxy, C 1-8 aliphaticoxy, C 3-20 aryloxy, thio, C 1-8 aliphaticthioxy, C 3-20 arylthioxy, heteroC 1-6 aliphatic, heterocyclic, C 3-20 aryl, C 3-20 arylC 1-6 aliphatic, heteroaryl, heteroarylC 1-6 aliphatic, acyl, acyloxy, amido, imido, sulfinyl, sulfonyl, amino, C 1-6 aliphaticamino, C 1-6 dialiphaticamino, C 1-6 trialiphaticamino, C 3-20 arylamino, C 3-20 diarylamino, carboxaldehyde, cyano, isocyano, azido, hydrazino, nitro, or halo;