Cryptands aluminum hydrides

Synthesis by high-dilution techniques requires slow admixture of reagents ( 8-24 hrs) or very large volumes of solvents 100 1/mmol). Fast reactions can also be carried out in suitable flow cells (J.L. Dye, 1973). High dilution conditions have been used in the dilactam formation from l,8-diamino-3,6-dioxaoctane and 3,6-dioxaoctanedioyl dichloride in benzene. The amide groups were reduced with lithium aluminum hydride, and a second cyclization with the same dichloride was then carried out. The new bicyclic compound was reduced with diborane. This ligand envelops metal ions completely and is therefore called a cryptand (B. Dietrich, 1969). 

The synthesis of 1,10-diaza-l 8-crown-6 (9) has been an important problem because this is the key starting material in the synthesis of numerous cryptands (see Chap. 8). Although first synthesized some years ago, the process has recently been patented. Di-azacrown 9 is prepared by a high dilution condensation of 1,8-diamino-3,7-dioxaoctane with ethylene glycol diacetyl chloride. The resulting diamide is then reduced with lithium aluminum hydride to give 9 in 56% overall yield from the open-chained diamine. The synthesis is illustrated In Eq. (4.8), below. 

Ellipsoidal cryptands can also be synthesized by direct alkylation procedures <77AG(E)720,80CB1487), obviating the need for a diborane or lithium aluminum hydride reduction step. In the case of [l.l.l]cryptand (15a) yields of the final amine alkylation step are enhanced by the amine proton itself acting as a template (81CC777). 

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