This invention provides processes for preparing compounds formula: wherein R is H, alkyl, acyl, aryl, aroyl or --C(O)R'; R' is alkyl or aryl; R.sub.1, R.sub.2, R.sub.4 and R.sub.5 are H, --OH, alkyl, cycloalkyl, alkoxy, halogen, fluorinated alkyl or alkoxy, --CN, --NH--SO.sub.2-alkyl, --SO.sub.2--NH-alkyl, alkyl amide, amino, alkylamino, dialkylamino, acyl, aryl or aroyl; R.sub.3 is H, alkyl, cycloalkyl, alkoxy, fluorinated alkyl, --NH--SO.sub.2-alkyl, --SO.sub.2--NH-alkyl, alkyl amide, amino, alkylamino, dialkylamino, fluorinated alkoxy, acyl, aryl, or aroyl; or a pharmaceutically acceptable salt thereof, as well as novel compounds useful in the synthesis of these compounds.