The present invention relates to ethynyl compounds of formula I wherein R1, R2, R2&prime；, R3, R3&prime；, R4, R4&prime；, U, V, W, Y, m, and n are as defined herein and to a pharmaceutically acceptable acid addition salts, to a racemic mixtures, or to its corresponding enantiomers and/or optical isomers and/or stereoisomers thereof. Compounds of formula I are allosteric modulators of the metabotropic glutamate receptor subtype 5 (mGluR5).
