This invention provides compounds of formula (I) wherein R1, R2, R3 and R4 are, each, independently, hydrogen, alkyl, alkenyl, alkynyl, alkoxy, aralkoxy, trifluoroalkoxy, alkanoyloxy, hydroxy, halo, trifluoromethyl, cyano, amino, mono- or di-alkylamino, alkanamido, or alkanesulfonamido; R5 is hydrogen, alkyl, alkenyl, alkoxyalkyl or alkylcycloalkyl; R6 is hydrogen, alkyl or alkenyl; X is oxygen or carbon; A is oxygen or NZ; Z is hydroxyl, alkoxy, aryloxy, carboxyalkyloxy of 2-7 carbon atoms, arylamino, or alkylsulfonylamino of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, which are useful in the treatment of arthritic disorders, colorectal cancer, and Alzheimer's disease.