Abstract Novel stable bicyclo [3.3. 0] octanic and bicyclo [4.2. 0] octanic 13, 14- didehydrocarbacyclins 1a–c, 2a bearing an achiral cyclohexanoic group at C-14 were synthesized. These analogues have been characterized by 13 C NMR spectroscopy. Compounds 1a–c and 2a were tested on rabbit and human platelet-rich blood plasma and 1a–c on rat stomach and guinea pig trachea smooth muscles. E-isomers of 1a–b were ...