The present invention relates to compounds of formula wherein R1 is C4-6-cycloalkyl or C4-6-heterocycloalkyl, which are optionally substituted by one or two substituents, selected from hydroxy or lower alkyl; A is phenyl, pyridinyl or piperidinyl; R2 is hydrogen, halogen, lower alkyl, cyano, C4-6-cycloalkyl, lower alkoxy, lower alkoxy substituted by halogen, or is a five- or six-membered heteroaryl, optionally substituted by lower alkyl; n is 1 or 2; or to a pharmaceutically acceptable acid addition salt, to a racemic mixture or to its corresponding enantiomer and/or optical isomers thereof. The compounds may be used for the treatment or prophylaxis of Alzheimer's disease, cognitive impairment, schizophrenia, pain or sleep disorders.