Procedure for preparing 11-(4-[2-(2-hydroxyethoxy)ethyl]-1-piperazineyl)-dibenzo[b,f] [1,4]thiazepine

The invention relates to a procedure for preparing quetiapine by reaction between a compound of formula (II) and a compound of formula (III), in which X means a leaving group and P a protective group of alcohols resistant to alkaline conditions, in the presence of a base, followed by a step of deprotection and, optionally, obtaining a pharmaceutically acceptable salt thereof. Said procedure permits the obtaining of quetiapine with a high degree of purity under soft temperature conditions, with short reaction times and avoiding the use of toxic solvents. (Graphic)