The present invention provides, for example, a compound of the following formula (I): 1wherein R1 is substituted amino and the like,R2 is halogen and the like,R3 is substituted or unsubstituted lower alkyl and the like,RA and RB are each independently hydrogen, substituted or unsubstituted lower alkyl and the like,RC and RD are each independently hydrogen, substituted or unsubstituted lower alkyl, or RC and RD together with the carbon atom to which they are attached may form a substituted or unsubstituted carbocycle, andring A is a carbocycle or a heterocycle,its pharmaceutically acceptable salt, or a solvate thereof as a therapeutic agent for diseases induced by production, secretion and/or deposition of amyloid-β proteins.
