Compounds of Formula I ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, W and X as defined in the specification, enantiomers thereof, pharmaceutically-acceptable salts thereof, processes for preparing them, pharmaceutical compositions containing them and their use in therapy, especially for treatment of conditions associated with reductions in nicotinic transmission. Compounds of the invention enhance the efficacy of agonists at nicotinic receptors.