Metal-ion promoted synthesis

In 1980, Kulstad and Malmsten M) reported an alkali metal ion promoted synthesis of [2.2.2]cryptand from l-iodo-8-chloro-3,6-dioxaoctane (77) and l,8-diamino-3,6-dioxaoctane (18) (Scheme 2). 

Also closely related to this theme are certain reactions involving the metal ion-promoted synthesis of (otherwise unstable) coordinated ligands such as cyclobutadiene, which are stabilized through coordination —e.g., the reaction described by Emerson, Watts, and Pettit (30),... 

Compounds of aza macrocycles are prepared by three main types of procedure (1) conventional organic synthesis of the ligand, (2) metal-ion-promoted reactions, involving condensation of non-cyclic components in the presence of a suitable metal ion, and (3) modification of a compound prepared by methods (1) or (2). 

Several cyclofunctionalization reactions of alkynic alcohols are synthetically useful. Metal ion-promoted cyclofunctionalization of ris-2-propargylcyclopentanol systems proceeds by the 5-exo mode (equation 77 and Table 23).197 Protiodemetallation or reductive demetallation provides the cyclic enol ether in high yields. This method has been used by Noyori in the synthesis of prostacyclin (PGh).197b,197c Reactions with catalytic amounts of mercury(II) or palladium(II) salts gave the endocyclic enol ether as the major product.197 -198 A related cyclization with Ag2C03 has been reported by Chuche.191 Schwartz... 

Although many synthetic routes have been adopted for the preparation of azacycloalkanes and -cyclophanes, the vast majority of cyclization procedures can be grouped into two major categories (i) direct synthesis by conventional organic reactions and (ii) metal ion-promoted (template) reactions. 

Potassium [7440-09-7] K, is the third, element ia the aLkaU metal series. The name designation for the element is derived from potash, a potassium mineral the symbol from the German name kalium, which comes from the Arabic qili, a plant. The ashes of these plants al qili) were the historical source of potash for preparing fertilisers (qv) or gun powder. Potassium ions, essential to plants and animals, play a key role in carbohydrate metaboHsm in plants. In animals, potassium ions promote glycolysis, Hpolysis, tissue respiration, and the synthesis of proteins (qv) and acetylcholine. Potassium ions are also beheved to function in regulating blood pressure. 

The use of metals for prearranging reaction centers as neighboring groups has a special value in the production of macrocycles (template effect). Although these ligands can be sometimes prepared directly, the addition of metal ion during the synthesis will often increase the yield, modify the stereochemical nature of the product, or even be essential in the buildup of the macrocycle. There have been few mechanistic studies of these processes. The alkali and alkaline-earth metal ions can promote the formation of benzo[18]crown-6 in methanol ... 

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