Helices, compound

Photosyntheses of Helical Compounds other than Helicenes. . . 76... 

A special type of photosynthesis of a helical compound is the irradiation of 1,1 -spirobi[benzindene] substituted with two tert. butyl groups 42) 58. 

By the irradiation of optically active 58 the helical compound 59 is formed stereo-specifically. However, this product (with the tert. butylgroups at a short distance) is thermolabile. It converts spontaneously into 60, already at 0 °C, thus showing mutarotation. The process was followed by ORD, which showed a complete reversal of the spectrum. 

A helical compound, lacking even three rings is the o.quaterphenylophan 67 47). It looks like the overbridged heptahelicene 37. 

Finally, it is noted that suitable enantiomers of helicenes have been applied as selector for non-helical compounds. The disodium salt of P-( +)-7,10-dicarboxy hexahelicene coated on silicagel was successfully used in resolving the N-(2,4-dinitro-phenyl)-a-amino acid esters. Good resolutions were found for alanine, isoleucine, valine, phenylalanine and phenylglycine 94). 

Let us now put the above principles into practice by considering the assembly of multiple-helical compounds. A simple chemical model for the formation of helicates involves the twisting of molecular threads , as shown in Figure 7-27. The incorporation of metal-binding domains into these threads allows the use of metal ions to control the twisting. 

Atropisomeric conjugated oligoalkenes can also be classified as helical compounds. Such structures are represented by s-cis- or s-rra j-butadiene derivatives bearing voluminous substituents which cause anticoplanar conformations. 

The helical compounds 198a and 199 were separated into the enantiomers by inclusion chromatography (medium-pressure column chromatography on cellulose triacetate). 200 was enantiomerically enriched (—)-200 was only weakly enrich-... 

Very recently Zhou et al. used twisted rigid ligands to synthetize compounds based on Keggin clusters with left- and right-handed hehcal chains [148] (see Fig. 3.24). Helical compounds based on HPAs have attracted attention because of their attractive structural features and potential applications, for instance, in asymmetrical catalysis. The chains are further extended to three-dimensional supramo-lecular structures by hydrogen bonds. The methylene blue dye has been photocatalytically bleached in the presence of this solid. Stacking of the chains leads to small pore-size and narrow pore-size distribution which are not beneficial for the photocatalytic activity. 

Zhou S, Liu B, Li X, Shi T, Chen Y (2014) Two new helical compounds based on Keggin clusters and N-donor multidentate ligand syntheses, structures and properties. J Solid State Chem 219 15-20... 

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