Provided herein are compounds useful for treating cognitive dysfunction and negative symptoms associated with CNS disorders. In aspects, a compound of formula (I') is [Image disponible dans le document PDF, Image available in the PDF document] and the others are independently CH, CF, CCF<com:Sub>3< / com:Sub>, CCH<com:Sub>3< / com:Sub> or COCF<com:Sub>3< / com:Sub>; R<com:Sup>1< / com:Sup> is phenyl, CN, F, OCF<com:Sub>3< / com:Sub>, C<com:Sub>1< / com:Sub>-C<com:Sub>3< / com:Sub> alkoxy or C<com:Sub>1< / com:Sub>-C<com:Sub>5< / com:Sub>
alkyl; R<com:Sup>2< / com:Sup> is H, C<com:Sub>1< / com:Sub>-C<com:Sub>5< / com:Sub>
alkyl or C<com:Sub>1< / com:Sub>-C<com:Sub>5< / com:Sub> alkoxy; R<com:Sup>3< / com:Sup> is H or CH<com:Sub>3< / com:Sub>; or R<com:Sup>1< / com:Sup> and R<com:Sup>2< / com:Sup> together represent an optionally substituted 5 or 6-membered O-containing heterocyclylene, optionally substituted 5 or 6-membered O-containing heteroarylene, or optionally substituted 5 or 6-membered
arylene; and R<com:Sup>4< / com:Sup> and R<com:Sup>5< / com:Sup> are independently H or C<com:Sub>1< / com:Sub>- C<com:Sub>4< / com:Sub>
alkyl, or R<com:Sup>4< / com:Sup> and R<com:Sup>5< / com:Sup> together represent an optionally substituted 4-7 membered cycloalkylene or optionally substituted 5-7 membered heterocycylene. Also provided are medicaments, compositions and therapuetic uses thereof.