The present invention relates to ethynyl derivatives of formula I wherein Y is N or C&mdashR3 R3 is hydrogen, methyl, halogen or nitrile R1 is phenyl or pyridinyl, each of which is optionally substituted by halogen, lower alkyl or lower alkoxy R2/R2&prime are each independently hydrogen, lower alkyl or lower alkyl substituted by halogen, or R2 and R2&prime together with the N-atom to which they are attached form a morpholine ring, a piperidine ring or an azetidine ring, each of which is unsubstituted or substituted one or more substituents selected from lower alkoxy, halogen, hydroxy and methyl R4/R4&prime are each independently hydrogen or lower alkyl, or R4 and R4&prime together form a C3-5 cycloalkyl-, tetrahydrofuran- or an oxetane-ring 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. Compounds of formula I are positive allosteric modulators (PAM) of the metabotropic glutamate receptor subtype 5 (mGluR5).
