(C3-7)cycloalkyl, ???OH, ???O(C1-6)alkyl, ???SH, ???S(C1-6)alkyl, ???NH2, ???NH(C1-6)alkyl and ???N((C1-6)alkyl)2; wherein the (C1-6)alkyl is optionally substituted with hydroxy, cyano or oxo; R6 and R7 are each independently selected from H, halo, (C1-6)alkyl and (C1-6)haloalkyl; with the proviso that when bond a is a single bond and bond b is a double bond; and X is NR1; R1 is H; and R2 is O; a