Wittig poly

Z. Yang and H. J. Geise, Preparation and electrical conductivity of blends consisting of modified Wittig poly(p rcr-phenylene vinylene), iodine and polystyrene, polymethyl methacrylate or polycarbonate, Synth. Met. 47 105 (1992). 

Although the methods reviewed above have been most widely used for synthesis of conducting polymers, there are many other organic reactions capable of producing conjugated structures. One example is the Wittig condensation of bis-triphenyl-phosphonium compounds with dialdehydes in the presence of a strong base, typified by the synthesis of poly(p-phenylene-vinylene) 102). 

The synthesis of poly-dibenzylidene-l,3-dithietane 201 is based on the Wittig reaction of/ -xylcnc-bis(triphcnyl-phosphonium) chloride 199 with carbon disulfide <2001MM346, 2002MM3806>. The phosphonium salt 199 was converted to the ylide 200, which reacted with carbon disulfide, yielding, after methanolysis, a thioketene. The latter was stirred at room temperature for 12 h to provide the polymeric compound 201, bearing 1,3-dithietane moieties in 54% yield (Scheme 25) <2001MM346, 2002MM3806>. 

Tellurophene aldehydes and ketones readily undergo reduction reactions typical of carbonyl compounds. The Wittig reaction of 2,5-bis(dodecyloxy)- -xylene-bis(triphenylphosphonium bromide) with tellurophene-2,5-dicarbaldehyde leads to poly(2,5-tellurophenediylvinylene) (MW 7000-29000 Da) in 65% yield <1995MM8363>. The condensation reactions of 2,5-diphenyl-3,4-diformyltellurophene 15 have been employed for the synthesis of a number of bi- and polycyclic heterocycles with a fused tellurophene ring (Scheme 8) <1976CB3886>. 

A variety of other poly-furans have been employed in Wittig reactions as either the aldehyde or the ylide component. Condensation of 5,5 -thiodi-2-furaldehyde (176), for instance, with the 2,2 -bifuryl-5,5 -diylbis-(methylenetriphenyl-phospho-nium bromide) (177) under basic conditions, gave the macrocycle 178 as orange crystals in 1.3% yield (Scheme 29) [148]. Two macrocyclic annulenones 182 and 184 were also obtained [149] from the base induced condensation of 181 with the dialdehydes 180 or 183, respectively. Both products are obtained in moderate yields (12-15%) and are highly colored solids (Schemes 30 and 31, respectively). 

In addition to phytoene (23), prepared as a mixture of the oW-trans- and 15-c/x-isomers by Wittig condensation, several model compounds with a similar triene chromophore have been produced.A range of poly-c (poly-Z) isomers of the C20 phytoene analogue has been synthesized. ... 

Another attempt shows the synthesis of HMF-derived vinyl polymers (Fig. 6) [38]. By the Wittig reaction, HMF and the methylated derivative 5-(methoxy-methyl)furfural (MMF) could be converted into vinyl derivatives. Radical polymerization leads to the corresponding vinyl polymers which might become substitutes for commodity polymers like polyethylene, poly vinyl chloride, and polystyrene. 

Bipyridine may be incorporated into a poly(/>ara-phenylene vinylene) chain by Wittig reactions, yielding 25. Solubilizing groups are necessary to characterize the polymer, whose absorption spectmm responds to a wide variety of metal ions in solution (ionochromism) [62]. The emission was also affected by different metal ions in different ways. It was proposed that metal ions that bind to both pyridine groups lead to a planarization of the chain and a quenching of the emission, whereas those that bind to only one pyridine group merely red shifted the emission. 

In phosphazene chemistry, preparation and reactions of small molecule, linear phosphazenes continue to attract interest. This year numerous papers have explored the utility of the aza-Wittig reaction in the synthesis of complex molecules with particular reference to nitrogen heterocycles. In cyclophosphazene chemistry, the shift of emphasis to materials which are monomers themselves or models for phosphazene polymers is apparent. The synthesis and characterization of poly(phosphazenes) is an active area with extensive interest in phosphazene based polyelectrolytes being noted. Solid state NMR has been shown to be a valuable tool for the study of both structure and phase changes in poly(phosphazenes). 

Wittig reaction. The poly(ethylene glycol)-linked bis(triphenylphosphine) (3) is a precursor of Wittig reagents Upon P-alkylation, the phosphonium salts are used. 

A general synthesis for all diastereomeric L-hexoses, as an example for monosaccharides that often do not occur in the chiral pool, has been worked out. The epoxidation of allylic alcohols with tertiary butyl hydroperoxide in presence of titanyl tartaric ester catalysts converts the carbon-carbon double bond stereose-lectively to a diol and is thus ideally suited for the preparation of carbohydrates. The procedure is particularly useful as a repetitive two-carbon homologiza-tion in total syntheses of higher monosaccharides and other poly hydroxy compounds. It starts with a Wittig reaction of a benzylated a-hydroxy aldehyde with (triphenylphosphoran-ylidene)acetaldehyde to produce the olefinic double bond needed for epoxidation. Reduction with sodium-borohydride... 

The synthesis of a gas-generating composition starts with the synthesis of a poly(vinyltriazole). A substituted triazole salt is added to a free radical brominating reagent, such as A-bromo succinimide, and to a radical initiator to form a brominated triazole. The brominated triazole is then added to triphenylphosphine to form a Wittig salt. Formaldehyde in alkaline medium effects the formation of a vinyltriazole salt, which can be polymerized with AIBN and a catalytic amount of a cationic initiator or a Ziegler-Natta catalyst. The reaction sequence is shown in Figure 9.10. 

Poly(arylene vinylene) derivatives were prepared by Wittig reaction of diphosphonium compounds(I and V), and dialdehyde compounds , Ill,and IV) as shown in Figurel. When I and II, I and IE, I and IV, and V and II are used, soluble alternating copolymers of (A), (B), (C), and (D) are obtained respectively(16,17,18). The diphosphonium compounds were prepared using triphenylphosphine and... 

To construct the B-ring, the unprotected hydroxymethyl group of the poly-hydroxypyrrolidine was oxidized into an aldehyde and a Wittig reaction was used to install the required ketone functitm at C-2 providing intermediate 87, ready for the subsequent nucleophilic cycUzation of the free amine (Scheme 18). Several subsequent catalytic hydrogenation steps were performed to provide, first the ketone 88, which was then submitted to the addition of HCl under an hydrogen atmosphere to achieve the N- and 0-deprotection leading to the amine 89. 

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