The present invention relates to ethynyl derivatives of formula Iwherein X is N or CH； G is N or CH； with the proviso that maximum one of X or G can be nitrogen； R1is phenyl or pyridyl, which are optionally substituted by halogen, lower alkyl or lower alkoxy； R2is hydrogen, lower alkyl or may form together with R4a C3-C6-cycloalkyl； R3/R3'/R4/R4'are independently from each other hydrogen, lower alkyl or CF3； or to a pharmaceutically acceptable acid addition salt, to a racemic mixture, or to its corresponding enantiomer and/or optical isomer and/or stereoisomer thereof.It has now surprisingly been found that the compounds of general formula I are positive allosteric modulators (PAM) of the metabotropic glutamate receptor subtype 5 (mGluR5).本發明係關於一種式(I)之乙炔基衍生物：或其醫藥學上可接受之酸加成鹽、外消旋混合物，或其對應之對映異構體及/或光學異構體及/或立體異構體，其中X 係N或CH；G 係N或CH；其中限制條件為X或G中最多一個是氮；R1係選擇性地經鹵素、低碳數烷基或低碳數烷氧基取代之苯基或吡啶基；R2係氫、低碳數烷基或可與R4共同形成C3-C6-環烷基；R3/R3'/R4/R4'係彼此獨立地為氫、低碳數烷基或CF3。令人驚訝地，現已咸發現通式I化合物係代謝型麩胺酸受體亞型5(metabotropic glutamate receptor subtype 5；mGluR5)之正向變構調節劑(positive allosteric modulator；PAM)。
