NEW MATERIAL:A dibenzo[b,f]thiepin derivative expressed by formula I (R1 is H or lower alkyl; R2 is H or esterified carboxy, or R1 and R2 together form phthaloyl; A is lower alkylene; X is halogen), and a salt thereof.

EXAMPLE: 8-Chloro-10-[ 2-( N-ethoxycarbonyl-N-methyl )ethoxy ]dibenzo[b,f]thiepin.

USE: A medicine having a suppressing action on the central nervous system, and an intermediate therefor.

PROCESS: A compound of formula II is reacted with a compound of formula III (Y is acid residue) to give a compound of formula Ia (R2a is esterified carboxy), which is then hydrolyzed if necessary. The hydrolysis product is decarboxylated to form the compound of formula I (R2 is H).