2-Formyl helicene

M)-[ll]-, and (M)-[13]-helicene 31). Wittig reactions between (M)-(—)-formyl-hexahelicene and suitable phosphonium salts led to 1,2-disubstituted ethylenes, all containing the same chiral moiety, which could be subjected to photocyclodehydrogenation (Table 1). 

The potentials for the rotation of the 1-substituents in 1-formyl- and 1-acetylhexa-helicene were calculated by Lindner 148). For both helicenes two minima were present, differing 8 kJ/mol from each other, and separated by barriers of 29-60 kJ/mol. 

Both X-ray crystallographic studies and theoretical predictions have been done to show that these sexithiophenes take a helical conformation. Internal torsional forces between rings have been used to drive the molecule to take a solid state helical conformation. Synthesis of tetrathia-[7]-helicene (TH[7]) 85 has been carried out by McMurry coupling of 2-formyl-benzo[l,2-i 4,3-... 

Subsequently they utilized the cobalt-mediated asymmetric synthesis of [7]helicene-like molecules described above in helicene-based phosphite ligand synthesis. The application of ligand P,S)-2 to rhodium-catalyzed asymmetric hydro-formylation revealed excellent regioselectivity, although the enantioselectivity was low (Scheme 10.14) [15]. For iridium-catalyzed asymmetric allylic amination, the... 

The first representative of a new type of helical structure (419), having features of both helicenes and cyclophanes, has been formed by pyrolysis of a sulphone made from the bis(bromomethyl)-quaterphenyl (420a) and the corresponding dithiol (420b). An intramolecular carbene-insertion reaction involving the helicene skeleton has been reported in which l-formyl-[6]helicene toluene-p-sulphonylhydrazone (421) is converted into (422), the structure of which has been determined unambiguously by H and n.m.r. spectroscopy. 

On refluxing in benzene, the l-formyl[6]helicene tosylhydrazone (29), in the presence of sodium hydride, gave the carbene-insertion product (30), whose structure was confirmed by an X-ray diffraction study. Resolution of the new hydrocarbon has been achieved by h.p.l.c., using a silica-gel column impregnated with (- )-TAPA [2-(2,4,5,7-tetranitro-9-fluorenylideneamino-oxy)propionic acid]. ... 

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