The present invention relates to ethynyl derivatives of formula I X, G, R1, R2, R3, R3&prime, R4, R4&prime, R5, R6, R6&prime, m, and n are as defined herein 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). They can be used for the treatment of schizophrenia or cognitive disorders.