Compounds of formula I: ##STR1## wherein R, R.sup.1, R.sup.2, R.sup.3, and R.sup.4 have any of the values defined in the specification, and their pharmaceutically acceptable salts, are inhibitors of aromatase, and are useful for treating diseases such as breast cancer, in mammals. Also disclosed are pharmaceutical compositions, processes for preparing compounds of formula (I) and intermediates useful for preparing compounds of formula I.