The present invention relates to phenylethynyl compounds of formula I wherein R1, R2, X, L, R3, R4, R4′, cyc, and n are as defined in the specification and claims and 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 are useful for the treatment of schizophrenia or cognitive diseases.