<p>The present invention refers to a process for preparing a compound of formula<br /> (I) or a pharmaceutically acceptable salt thereof:</p> <p>wherein R is (C:-C&nbsp; r o)alkyl, or co-trifluoro(Cr-Cro)alkyl; N,RU I &amp; Rr and R2 aro, independently, hydrogen, hydroxy, (Cr-Cs)alkoxy, (Cr-Ca) alkylthio, 10 halo, trifluoromethyl<br /> or 2,2,2-trifluoroethyl; or one of Rr and Rz is in ortho position to the R-&nbsp;O-<br /> group and, taken together with the same R-O-, represents a (Cz-Ce)alkyl;<br /> R.&lt; o- o-&nbsp; group where Ro is R: and R+ &amp;re, independently, hydrogen, (Cr-Ca)alkyl;<br /> or Ra is hydrogen and Rs is a group selected from -cHz-oH, -cHz-o-(cr-co)alkyl,<br /> -cH(cH:)-oH, -(cHz)z-S-CH3, benzyl 15 and 4-hydroxybenzyl; or Ra and<br /> Rs, taken together with the adjacent carbon atom, form a (C:- Ce)cycloalkyl<br /> residue; Rs and Ro are independently hydrogen or (cr-co)alkyl; or taken<br /> together with the adjacent nitrogen atom form a 5-6 membered monocyclic<br /> saturated heterocycle, optionally containing one additional heteroatom<br /> chosen among -O-, -S- and -NRz- where Rz is hydrogen 20 or (Cr-Co)<br /> alkyl; R4 R3 and wherein optionally one or more hydrogen atom in the goups R, Rt, Rz, R:, Rr,<br /> Rs and Ro, preferably in the R group, can be substituted by a deuterium<br /> atom.</p> <p>&nbsp;</p>