NEW MATERIAL:A dibenzothiepin derivative of formula I (R is OH or amino group).

EXAMPLE: 2-(10,11-Dihydro-11-oxodibenzo [b,f] thiepin-4-yl)-propionamide.

USE: Antiphlogistics.

PROCESS: 2-[2-(α-Cyanoethyl)-phenylthio]phenylacetic acid of formula II or its reactive derivative is subjected to ring closure in the presence of a condensing agent, e.g. polyphosphoric acid, in a solvent, e.g. benzene, at 70W200°C to give the compound of formla I (R is NH2), which is hydrolyzed in the presence of an acid or base in water or a hydrous organic solvent to form the compound of formula I (R is OH). The starting compound of formula II is obtained by reacting a compound of formula III ( R' is ester residue; A is halogen or mercapto group) with a compound of formula IV (B is halogen or mercapto group; A is not the same as B).