The present invention provides a compound which has an effect of inhibiting amyloid-β production and is useful as a therapeutic agent for diseases induced by production, secretion and/or deposition of amyloid-β proteins. The present invention relates to a compound represented by formula (I) or a pharmaceutically acceptable salt or solvate thereof: wherein A is optionally substituted carbocyclic diyl or optionally substituted heterocyclic diyl; B is an optionally substituted carbocyclic group or an optionally substituted heterocyclic group; R1 is a group such as optionally substituted lower alkyl; R2 is a group such as hydrogen; and R3a and R3b are each independently a group such as hydrogen, provided that the following compound is excluded.