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

Here we report on the possibility of using rotaxane wheels as noncovalent protecting groups which significantly decrease the activity of functional groups 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. The catalytic hydrogenation of these two rotaxanes proceeds slower than those of the corresponding free axle compounds 6a and 6b, indicating steric hindrance of the C=C double bond by the wheel of the rotaxane in each case. Nontheless, 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 the centre of the axle.