The invention relates to compounds of the general formula ##STR00001## in
which R.sup.1, R.sup.2, R3, R.sup.4, R.sup.2', R3', R.sup.4', R.sup.5,
and X is --CHR-- are as defined in the specification. The invention also
provides pharmaceutically acceptable acid addition salts, optically pure
enantiomers, racemates and diastereomeric mixtures of such compounds. The
invention further provides methods for the treatment of Alzheimer's
disease or common cancers.