The compounds of formula I: ##STR1## wherein R.sub.1 and R.sub.2 are hydrogen, alkyl or cyclic or bicyclic alkyl; R.sub.3 is formyl, alkanoyl, alkenoyl, alkylsulfonyl, aroyl, arylalkenoyl, arylsulfonyl arylalkanoyl or arylalkylsulfonyl; A is a substituted phenyl group of the following formula: ##STR2## wherein R.sub.5 is cyano and R.sub.6 is alkyl, chloro, bromo, fluoro or iodo and pharmaceutically acceptable salts thereof, are smooth muscle relaxants.