Stoddart

C. D. Gutsche in J. F. Stoddart, ed.. Monographs in Supramolecular Chemisty, Calixarenes, Royal Society of Chemistry, Cambridge, England, 1989. Ethyl 702, Technical Bulletin, Ethyl Corporation, Baton Rouge, La. 

F. Stoddart, Cyclodextrins, Royal Society of Chemistry, London, 1989. 

Stoddart and his coworkers have reported syntheses of the trans-syn-trans and the trans-anti-trans isomers of dicyclohexano-18-crown-6 The synthesis of these two compounds from trans-l,2-cyclohexanediol was accomplished in two stages. First, the diols were temporarily linked on one side by formation of the formal, and this was treated with diethylene glycol ditosylate and sodium hydride to form the hemi-crown formal. Removal of the formal protecting group, followed by a second cychzation completed the synthesis. The synthesis of the trans-anti-trans compound is illustrated below m Eq (3 12) and the structures of the five possible stereoisomers are shown as structures 1—5. 

As in the previous categories in this section, there are numerous compounds which have been prepared based on a sugar subunit. Examples may be found in Refs. 7,35,42-45, 57, 82-85, 117—121,175,176,193 and 208. Much of the work in these references has been reported by Stoddart and his coworkers, who have pioneered this field. As with the compounds prepared by Cram, the goal was to prepare a chiral receptor for ammonium ions which could be utilized in enzyme model studies. 

Although the clam structures are of interest as ammonium ion binders, they are by no means the only azacrown compounds of interest in this application. Sutherland and coworkers have examined a number of azacrowns as primary ammonium ion bind-ers - . In addition, Metcalfe and Stoddart have utilized bis-azacrowns to bind secondary ammonium cations. 

Diazacrown compounds have been studied extensively by the groups of Sutherland and Stoddart . Particular emphasis has been placed on the inter-... 

Coxon and Stoddart have directed their attention to the formation of penta-erythritol-derived cryptands. With these molecules, the strategy was to block one pair of hydroxyl groups as an acetal and form a crown from the remaining diol. In the first of the two reports cited above, this was accomplished by treating the 0-benzylidine derivative of pentaerythritol with base and diethylene glycol ditosylate. The crown was then treated with a mixture of UAIH4 and BF3 which gives partial reduction of the acetal as shown in (8.9), above. The monoprotected diol could now be treated in a fashion similar to that previously described and the benzyloxy cryptand (77) would result. The scheme is illustrated below as Eq. (8.10). 

Krespan has utilized these substances in the preparation of a variety of azacrowns and cryptands . Note that this material is also mentioned by Coxon and Stoddart . The strategy and techniques utilized with 14 are similar to those discussed above and are not noted here in detail. An overall transformation is illustrated in Eq. (8.12). 

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