Synthesis of the semi-rigid analogues of prothiadene and dithiadene as potential antidepressant and antihistamine agents: 11-[2-(Dimethylaminomethyl)cyclohexylidene]-6,11-dihydrodibenzo[ b,e ]thiepins and 4-[2-(dimethylaminomethyl)cyclohexylidene]-4,9-dihydrothieno-[2,3- c ]-2-benzothiepins