Abstract: Unsaturated alcohols, thiols and thioesters are cyclized by a phenyl selenenyl halide; wherein the conformation flexibility of the unsaturated alcohol, thiol or thioester is selected such that the hydroxy group, thiol group or thioester group is capable of internal addition to at least one unsaturated bond in said alcohol, thiol or thioester; and wherein the ratio of the phenyl selenenyl halide to said unsaturated alcohol, thiol or thioester is 0.9-1.5 to 1. In a preferred embodiment, oxygen isomers and sulfur analogs of prostacyclin of the formula ##STR1## wherein X= ##STR2## Y=(E)- and (Z)- >C.dbd.CH--CH.sub.2 CH.sub.2 CH.sub.2 COOR; (E)- >CH--CH.dbd.CH--CH.sub.2 CH.sub.2 COOR; andR=any pharmaceutically acceptable cation or lower alkyl group comprising 1 to 4 carbon atoms are formed by:(1) cyclizing a PGF.sub.2.alpha. prostaglandin derivative or a 9.alpha. thio or 9.alpha. -thioester analog of prostaglandin PGF.sub.2.alpha.

Abstract: Stable biologically active aromatic prostacyclin analogues of the formula ##STR1## wherein X represents ##STR2## and R represents hydrogen, a pharmaceutically acceptable cation or a pharmaceutically acceptable lower alkyl group, are useful in the treatment of blood platelet aggregation and vascular constriction.