Chemical reactions in the axle of rotaxanes - Steric hindrance by the wheel

Here we report on the possibility of using rotaxane wheels as noncovalent p rotecting groups which significantly decrease the activity of functional gr oups in the central part of the axle. The amide-linked rotaxanes 5a and 5b, each containing a C=C double bond in their axle, have been synthesised. Th e catalytic hydrogenation of these two rotaxanes proceeds slower than those of the corresponding free axle compounds 6a and 6b, indicating steric hind rance of the C=C double bond by the wheel of the rotaxane in each case. Non theless, the rotaxane 9 with an aliphatic (succinic acid) middle region in its axle can be prepared in this manner. Dehydrobromination of the axle in the rotaxane 15 yields the rotaxane 16 with a C=C triple bond located in th e centre of the axle.