The invention relates to compounds of the formula ##STR1## wherein *B is ##STR2## Y is O or S, *A is *--(CH.sub.2).sub.n --(X).sub.m --(CH.sub.2).sub.r --, n or r, independently, are integers from 0 to 3, m is an integer from 0 to 1, provided that when m is 1, then n must be at least 1, X is O or S, R.sub.1 and R.sub.4, independently, are hydrogen, lower alkyl, hydroxy or lower alkoxy, provided that when *B is other than ##STR3## at least one of R.sub.1 and R.sub.4, and one of R.sub.6 and R.sub.7 must be hydrogen, R.sub.2 and R.sub.3 are independently hydrogen, lower alkyl, cycloalkyl, halogen, nitro, lower alkoxy, lower alkenyl, lower alkynyl or aryl, R.sub.5 and R.sub.6, independently are hydrogen or lower alkyl, R.sub.7 is hydrogen, lower alkyl, cycloalkyl or aryl, Het is a monocyclic 5- or 6-membered hetero aromatic or a bicyclic heteroaromatic radical containing one or two hetero atoms selected from nitrogen oxygen and sulfur, which radical may be substituted by lower alkyl, halogen or aryl, and the asterisk denotes the point of attachment, and when R.sub.6 and R.sub.7 are different, their enantiomers and racemic mixtures thereof, and pharmaceutical acceptable acid addition salts thereof.The compounds of formula I exhibit activity as Platelet Activating Factor (PAF) antagonists and are, therefore, useful as agents for the prevention and treatment of vascular diseases, pulmonary diseases, dermatological disorders, transplant rejection, immunological disorders and inflammatory conditions.