NEW MATERIAL:A propionic ester derivative of formula I: (R is lower alkyl group; A is O or S; X is an oxygen or two hydrogen atoms; Y is CH or N).

EXAMPLE: Ethyl 2-[10,11-dihydro-11-oxo dibenzo [b,f] thiepin-2-yl]-propionate.

USE: Anti-inflammatory drugs.

PROCESS: A compound of formula IV: R' is OH or amino group) or its reactive derivative is reacted with a lower alcohol in the presence of a mineral acid, e.g. sulfuric, hydrochloric acids, etc. to give the compound of formula I. The reaction is preferably carried out at room temperature to 200°C for 1W5 hr.