Thiophen Analogues of Helicenes

Thiophen Analogues of Helicenes.— The photocyclization with iodine as oxidant of 1,2-di(diheteroaryl)ethenes, in which the heteroaryl group is derived from benzo[fe]thienyl or from tricyclic systems such as (434) or (440), is the key step in the synthesis of heterohelicenes. The ethylenes in turn are prepared from the aldehydes and the chloromethyl derivatives via phos-phonium salts or phosphonates through the Wittig reaction. The Bestmann method was also used for the synthesis of symmetrically substituted ethylenes from phosphonium periodates. Thus from (443) the heterohexahelicene (444) was obtained, (445) gave (446), and the hetero-heptahelicene (448) was obtained from (447). The undecahelicene (450) was prepared from (449). - These syntheses illustrate the fact that heterohelicenes are more easily available than helicenes, as the necessary aldehyde is prepared by metalation of (448) with butyl-lithium followed by reaction with iV-methylformanilide. The heptahelicene (452) was obtained by a double photocyclization of (451). 

Several of the helicenes have been resolved by manual crystal separation, and in one case resolution was also achieved by recrystallization from an optically active solvent. The n.m.r. and mass spectra of these compounds have been studied in detail.  

The electronic spectra of a number of heterohelicenes have been discussed. The optical rotatory dispersion and circular dichroism spectra of the resolved one were measured. Calculation on a model compound was performed to establish the absolute configuration. The right-hand chirality was assigned to the (+)-heterohelicenes. An. ST-ray analysis of (444) 

The heterohelicenes can be used for the synthesis of a new class of polycyclic aromatic compounds, similar to coronene or corannulene, for which Wynberg suggests the name heterocirculenes. Thus the hetero-hexahelicene (446) gives (453) in 95% yield upon heating for several minutes at 140 ° with an AlCls-NaCl melt, and upon reaction with maleic anhydride and chloranil (453) yields (454). Decarboxylation of the latter or the corresponding acid with copper powder in quinoline furnishes the hetero-circulene (455).  

Thiophen Analogues of Helicenes.— The reaction of seven heterohelicenes with AICI3 has been described. The products were compounds in which the two helical termini of a helicene are connected by a or-bond. The intramolecular ring-closure was limited to hetero-[5]- and -[6]-helicenes. A series of regularly annelated thiaheterohelicenes has been prepared by a new progressive annelation technique based on the key intermediate 2-methylbenzo[l,2-6 4,3-6 ]dithiophen. Two methano-bridged heterohelicenes have been prepared. The synthesis of some 

Claeys, E. Deray, M. Descamps, J. Bauthier, J. Richard, and R. Charlier, Chim. 

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Thiophen Analogues of Helicenes.— By the use of thieno[2,3-h]thiophen as building block and by the use of double photocyclization, the heterohexa-helicenes (332)—(335) were prepared and their n.m.r. and u.v. spectra discussed. New heterohelicenes containing seven-membered rings have been synthesized. From the compound (336), the azepine derivative (337) was obtained by treatment with benzylamine and sodium dithionite. The helical nature of the azepine was revealed by the non-equivalence of the geminal protons." ... 

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