Octopus molecules

Inclusions of Other Grown Analogues. A variety of crown analogues and hybrid modifications (24—28) with other topological features (lariat ethers (31,32), octopus molecules (33), spherands (eg, (12) (34), torands (35)) including chiral derivatives (36) have been prepared and demonstrated to show particular inclusion properties such as chiroselective inclusion (Fig. 4) (37) or formation of extremely stable complexes (K ">(LR) for (12)... 

Both of these structures are open-chained compounds corresponding to crown ethers in function if not exactly in structure (see Chap. 7). They have repeating ethyleneoxy side-chains generally terminated in a methyl group. Montanari and co-workers introduced the polypodes 22 as phase transfer catalysts . These compounds were based on the triazine nucleus as illustrated below. The first octopus molecule (23) was prepared by Vogtle and Weber and is shown below. The implication of the name is that the compound is multiarmed and not specifically that it has eight such side-chains. Related molecules have recently been prepared by Hyatt and the name octopus adopted. For further information on this group of compounds and for examples of structures, refer to the discussion and tables in Chap. 7. 

In specific applications to phase transfer catalysis, Knbchel and his coworkers compared crown ethers, aminopolyethers, cryptands, octopus molecules ( krakenmole-kiile , see below) and open-chained polyether compounds. They determined yields per unit time for reactions such as that between potassium acetate and benzyl chloride in acetonitrile solution. As expected, the open-chained polyethers were inferior to their cyclic counterparts, although a surprising finding was that certain aminopolyethers were superior to the corresponding crowns. 

The work of Hyatt on cyclotriveratrylene—derived octopus molecules contrasts with this. Of course, these species have the advantage of ligand directionality absent in the benzene-derived octopus molecules. Except for the shortest-armed of the species (i.e., n = 1), all of the complexing agents (i.e., n = 2—4) were capable of complexing alkali metal cations. Synthesis of these species was accomplished as indicated below in Eq. (7.7). These variations of the original octopus molecules were also shown to catalyze the reaction between benzyl chloride and potassium acetate in acetonitrile solution and to effect the Wittig reaction between benzaldehyde and benzyltriphenylphos-phonium chloride. 

Several years earlier (1974), the same group had already described manyarmed, albeit non-branched, molecules as octopus molecules [6], whose numerous arms were used for complexation with metal ions (Fig. 1.2). These octopus molecules can be regarded as forerunners of nitrogen-containing propylenamine cascade molecules since they already demonstrated the utility of many adjacent functional arms - all the more readily attainable by branching - for example for host-guest interactions [6]. 

Fig. 1.2 Octopus molecule (left) host-guest interaction with metal ions (schematic according to Vogtle, Weber)...

For a time one managed by choosing new descriptions and used intricate contractions and modifications of the available terms Some examples being clathrate complex, clathrate hydrate, hydrocarbon clathrate, gas hydrate, interlamellar sorbent, molecular compoimd, addition compound, loose addition complex, cascade complex, lock-and-key complex, super molecular complex, molecular complex associate, tweezer molecule complex, soccer molecule complex, hexapus molecule complex, octopus molecule complex as well as complexes or inclusion compounds of spherands, sepulchrands, coronands, cyclidenes, cryptands, cryptophanes, calixarenes, cucurbit-uril, annelides etc. 

Scheme 2 Glycosylation of an octopus molecule made by Baker and coworkers - a AcCN, NIS, AgOTf, reflux, 9% b PdlOHlj/C, Hj, 96%.

Cyclotriveratrylene, (C9Hio02)3, has the shape of a saucer (Fig. 28a). The molecule can be used as a base upon which to chemically construct the so-called octopus molecules (Fig. 28b). These molecules can be used to include molecules in solution as well as in the solid state. 

FIGURE 28 (a) Saucerlike structure of cyclotriveratrylene and (b) related octopus molecule. 

Although numerous substances have been utilized as phase transfer reagents in specific cases, very little comparative work is available. Such a study [48] is reported for what might almost be called the standard reaction for catalyst evaluation the displacement of chloride from benzyl chloride by acetate ion. Included in this study are yield and rate data (half lives are compared) for inter alia) several crown ethers, aminopolyethers, cryptates, an octopus molecule and nonactin [48]. Several generalizations are offered which will not be reiterated here. We note that such comparisons can be a valuable guide to catalyst selection. 

Octopus molecules in the cycloveratrylene series, such as (452), capable of adopting cavity-containing conformations, have been prepared. A multi-stage... 

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