A compound in all possible racemic, enantiomeric and diastereoisomer forms of the formula ##STR38## wherein Y is --O--, Z.sub.2 is --CF.sub.3, Z.sub.1 is --CN or --NO.sub.2, X is --O-- or --S--,R.sub.3 is hydrogen or alkyl of 1 to 4 carbon atoms optionally substituted by at least one halogen or --CN and R.sub.4 and R.sub.5 are individually alkyl of 1 to 4 carbon atoms optionally substituted with a member of the group consisting of halogen, --OH, esterified or esterified or protected hydroxy and phenylthio optionally substituted by halogen or --OH, and wherein at least one of R.sub.4 and R.sub.5 is substituted.