This invention provides a compound of the formula (I): wherein the ring A is an optionally substituted carbocyclic group or an optionally substituted heterocyclic group； R 1 is optionally substituted lower alkyl, optionally substituted lower alkenyl, optionally substituted lower alkynyl； R 2a and R 2b are each independently hydrogen, optionally substituted lower alkyl or optionally substituted acyl； R 3a , R 3b , R 3c and R 3d are each independently hydrogen, halogen, hydroxy or optionally substituted lower alkyl etc.； a pharmaceutically acceptable salt or solvate thereof, which is useful for treating diseases induced by production, secretion and/or deposition of amyloid ² protein.
