This invention relates to a compound or a pharmaceutically active acid addition salt of formula I. The compounds of formula I of the present invention is regulators of amyloid beta and thus disease associated with deposition of - amyloid in the brain, in particular Alzheimers disease, and other diseases such as cerebral vascular amyloid neuropathy, Dutch-type hereditary cerebral hemorrhage amyloidosis sex (HCHWA-D ), multi-infarct dementia, boxer may be useful in the treatment or prevention of Alzheimers and Downs syndrome. [Formula I] Wherein, Aryl Het I is O, S or a 5 or 6 membered heteroaryl group containing 1 to 3 heteroatoms selected from N and Het containing aryl II is O, or S, or a 5 or 6 membered heteroaryl group containing 1 to 3 heteroatoms selected from N, or O, 1 to 4 heteroatoms selected from S or N, at least one ring is aromatic character and a two membered ring system R 1 is lower alkyl, lower alkoxy, halogen-substituted lower alkyl, or halogen R 2 is halogen, lower alkyl, lower alkoxy, hydroxy, halogen-substituted lower alkyl, hydroxy-lower alkyl, or substituted or benzo [1,3] dioxin solril, or Optionally halogen, lower alkyl, lower alkoxy, S (O) 2 - lower alkyl, cyano, nitro, halogen-substituted lower alkoxy, dimethylamino, - (CH 2 ) p -NHC (O) O- lower alkyl, or halogen-substituted lower alkyl which is substituted by - (CHR) p - phenyl, wherein R is hydrogen, halogen, hydroxy or lower alkoxy, or Hydroxy or optionally halogen- or cycloalkenyl or cycloalkyl is substituted with substituted lower alkyl, or Optionally halogen, lower alkyl, lower alkoxy or substituted by dimethylamino, O, S or a 5 or 6 membered heteroaryl group containing 1 to 3 heteroatoms selected from N, or O- or phenyl optionally substituted by halogen, or Optionally halogen, hydroxy, a halogen-substituted lower alkyl or C (O) O- heterocycloalkyl substituted with lower alkyl R 3 is hydrogen, lower alkyl, cyano or phenyl R 4 is lower alkoxy, lower alkyl or halogen p is
