Wittig synthesis ethylene derivatives

Reactions with sodium hydride in dimethyl sulfoxide Wittig synthesis Ethylene derivatives... 

Lithium alkoxide Wittig synthesis Ethylene derivs. from 0X0 compds. and phosphonium salts... 

Triphenylphosphinelethylene oxide Ethylene derivatives from halides and 0x0 compounds Shortened Wittig synthesis... 

Wittig synthesis with As-ylids Synthesis of rraw -ethylene derivs. or trans Oxido compds. from aldehydes and arsonium salts... 

Wittig synthesis with As-yiides Ethylene derivatives from aldehydes Arsonium salts... 

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). 

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