No abstract

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 5aand 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 9with an aliphatic (succinic acid) middle region in its axle can be prepared in this manner. Dehydrobromination of the axle in the rotaxane 15yields the rotaxane 16 with a C≡C triple bond located in the centre of the axle.

The IUPAC notation system does not provide a nomenclature for interlocked, mechanically linked molecules beyond very simple catenanes and rotaxanes [1]. Whereas simple catenanes and rotaxanes like 1 and 2 can be named explicitly as [2]catenane and [2]rotaxane according to IUPAC, [1] one already brakes new ground with the naming of additionally bridged types of compounds -such as "pretzelanes" 3 [2] which are easily accessible nowadays.Abstract. We introduce a systematic nomenclature for mechanically linked molecules -such as catenanes, rotaxanes, and assemblies derived from these structural elements -which comes up to the increasing complexity of already synthesized interlocked molecules and the ones to be expected in future. Like in the naming of other substance classes (polycycles, ly used by chemists, if they are constructed from easily comprehensible characteristic parts, basing on immediately convincing rules. Like in the former cases mentioned above a new nomenclature seems to be sensible, which contains -analogously to the bicyclo nomenclature of von Baeyer and to the crown compounds, cyclophanes [3], podands [4], and dendrimers [5] -a characteristic part of the name, for example in brackets, so that it indicates the "overall structure" and its most important features, such as e.g. the type, number, and sequence of the mechanical bonds particularly relevant in this case. phanes, crown compounds, podands, dendrimers) we attach importance to the fact, that certain units in the name, e.g. expressions in brackets, quickly convey an idea of the molecular architecture. Furthermore, this modular nomenclature reveals as many analogies to the IUPAC nomenclature as possible.

No abstract

Besides by clipping [1], threading [2], and recently also by trapping [3] a wide range of rotaxanes has been obtained via the slipping method [4, 5]. As no templating interactions are required for a thermally promoted slipping of the wheels onto the axle, only the steric compatibility of the macrocyclic cavity and the size of the blocking group (stopper) is vital for a successful rotaxane synthesis. Hence, rotaxanes with pure hydrocarbon axles [4e, 5b,d,e] have become accessible by means of this method. Particularly simple and still very effective is the slipping procedure in the melt [5], in which the preformed components -axle and wheel -are heated to about 350 °C for one minute. Therefore, this method has been employed to examine the size complementarity of several pairs of macrocycles and stoppers [5b -d].Slipping and subsequent deslipping experiments allowed to determine sterically matching pairs of wheels and blocking groups and, thus, to infer the actual size of the macrocyclic cavity. Although modern computer calculations have very much improved during the last years, predictions of the compatibility of certain elements still seem to be difficult due to the size and complexity of supramolecular structures. Even the effective cavity size and shape depends on many factors, such as the constitution of the ring-forming elements [4f -g, 6], the conformation at a specific temperature [4c,d] the solvation, and other effects [2d], so that it is hard to prognosticate. Thus, reliable data on the cavity size still have to be obtained from experimental studies, such as slipping-Abstract. We report the synthesis of a series of new hydrocarbon macrocycles. Following the dithia-phane route, four large rings 3 -6 of the cyclophane type containing different numbers of ring atoms were prepared confirming the general applicability of this route compared to alternative macrocyclizations. Cycle 3 is the hydrocarbon analogue to the tetralactam and the sulfone amide macrocycles 1 and 2 used in Results and DiscussionSince the tetralactam macrocycle 1 was found to be complementary to the 3,5-di-tert-butylbenzene stopper, whereas the corresponding sulfonamide cycle 2 needs the larger blocking group p-tritylbenzene to form ro-many rotaxane syntheses. The macrocycles synthesized here are supposed to be uselful as wheels in the slipping approach to rotaxanes to further establish a reference system for the cavity size of cyclic compounds by comparing them to certain complemenatry blocking groups. The x-ray data obtained of the macrocycles 3, 5, and 6 reveal the cavity shape and size in solid state. 642