Abstract: New compounds of formula (I) wherein R.sub.1 is H, CH.sub.3, OCH.sub.3, NO.sub.2, NH.sub.2, CN, CF.sub.3, CHF.sub.2, CH.sub.2 F or halogen, R.sub.2 is a heterocyclyl radical selected from 1-imidazolyl, triazolyl, tetrazolyl, pyrazolyl, pyrimidinyl, oxazolyl, thiazolyl, isoxazolyl and isothiazolyl, R.sub.3 is H or OH, R.sub.4 is H, R.sub.5 is H or OH; or R.sub.4 is H and R.sub.3 and R.sub.5 combined form a bond; or R.sub.3 is H and R.sub.4 and R.sub.5 combined form --(O); R.sub.6 is methylene, ethylene, --CHOH--, --CH.sub.2 --CHOH--, --CHOH--CH.sub.2 --, --CH--CH-- or --C(--O)--; or R.sub.4 is H and R.sub.5 and R.sub.6 combined is --CH-- or --CH--CH.sub.2 --; stereoisomers thereof and non-toxic pharmaceutically acceptable acid addition salts thereof exhibit selective aromatase inhibiting properties, compared with their desmolase inhibiting properties. The compounds of the invention are valuable in the treatment of estrogen dependent diseases, e.g. breast cancer or benign prostatic hyperplasia (BPH).