Wittig oligo

The only example known for the formation of azetidine 82 by direct intramolecular aza-Wittig reaction is the reaction of the /3-azidoketone 81 with triphenylphosphane (Scheme 41). Attempts to transfer this reaction to 83 and 84 were not successful (87NKK1250). This failure can be attributed to the formation of intermediates with highly energetic transition states, where the rate of intramolecular attack on the carbonyl function is so slow that oligo- and polymeric compounds are preferentially formed. 

Oct-OPV5 and Ooct-OPV5 were prepared following a procedure that was used to prepare terf-butyl-end-substituted oligo(phenylene vinylenes) [43], Benzyltri-phenylphosphonium bromide was lengthened by a styryl unit via a Wittig reaction with 4-methylbenzaldehyde. The methyl group of the stilbene was functionalized by bromination with A -bromosuccinimide (NBS). The phosphonium salt of the stilbene was obtained by a subsequent reaction with triphenylphosphine in toluene. 

Both Wittig and Wadsworth-Emmons reactions have been used to synthesise functionalised oligo(vinylthiophenes) (245) for use as potential liquid crystal and non-linear optical materials. ... 

Ethinyl-substituted (oligo)thiophenes are e.g. obtained by the Wittig reaction of the corresponding aldehyde 72-74 with tetrabromomethane and triphenyl-phosphine which results in 1,1-dibromoethylene substituted thiophenes 75-77. Successive elimination of HBr and halogen/metal exchange with -BuLi leads, after aqueous work-up, to the desired acetylenes 78-80 in good overall yields [Eq. (34)] [26d]. 

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