Chiral macrocycle, metal containing

In more recent syntheses of chiral macrocycles containing pyridine units like 48, which are of interest in their reduced dihydropyridine-form as model compounds for the redox system NADH/NAD , the yield increasing effect of added cesium salts was also used [52]. The yield of 48 was doubled in the cyclization of bis-L-valine amide 47 with l,5-dibromoi ntane in DMF from 41 % (Na2C03) to 80% by application of CS2CO3. The results of cyclizations with several other alkali metal carbonates [52] are shown below. 

Despite the overall decline in output, the year has produced ftirther interesting developments in the fteld of hypervalent phosphorus chemistry. These include phosphoranes containing acetylenic links, the synthesis and enantiomeric separation of a bicyclic phosphorane with chirality only at phosphorus, and a wide range of phosphoranes incorporated within macrocyclic ring systems (Houlla et al). In addition Lattman has reported on phosphoranes bound to transition metals or enclosed within calixarene skeletons and Holmes and his co-workers have made further substantial contributions on the X-ray crystal structures of phosphoranes containing eight-membered rings. 

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