1, 4-Disubstituted butadienes

Grignard reagents in the presence of Ni-phosphine complexes remove tellurium from tellurophene to give 1,4-disubstituted butadienes. ... 

The combination of cis-trans isomerism with iso-syndio and erythro-threo dispositions gives complex stractures as exemplified by the 1,4 polymers of 1-or 4-monosubstituted butadienes, such as 1,3-pentadiene (72, 73), and 2,4-pentadienoic acid (74, 75) and of 1,4-disubstituted butadienes, for example, sorbic acid (76). This last example is described in 32-35 (Scheme 6, rotated Fischer projection). Due to the presence of three elements of stereoisomerism for each monomer unit (two tertiary carbons and the double bond) these polymers have been classed as tritactic. Ignoring optical antipodes, eight stereoregular 1,4 structures are possible, four cis-tactic and four trans-tactic. In each series (cis, trans) we have two diisotactic and two disyndiotactic polymers characterized by the terms erythro and threo in accordance with the preceding explanation. It should be noted that here the erythro-threo relationship refers to adjacent substituents that belong to two successive monomer units. 

The Arcus approach can be extended to the analysis of the polymerization of 1,4-disubstituted butadienes. The main differences concern the presence of a further element of stereoisomerism, the cis or trans configuration of the double bond in the chain, and the fact that the chemical monomer unit (—CHA—CH=CH—CHB—) does not coincide with the stereochemically significant chain segment (corresponding to =CH—CHB—CHA—CH=). 

There are four types of possible stereoregular structures for each frans-1,4 polymer of 1,4-disubstituted butadiene (Fig. 13). The stereochemistry of polymers is represented by two kinds of relationship as follows, one of which is the relative configuration between the two repeating monomer units. When all the... 

When a reaction like 7.8-3 is carried out thermally with a 1,4-disubstituted butadiene, the stereochemistry is very specific. Thus we have ... 

Figure 5.1 Stereoisomerism of cis-, A polymers of 1,4-disubstituted butadienes, poly(3,4-dialkyl-cw-l-butenylene) CH=CH CH(R) CH(R) n- or [-CH(R>-CH=CH—CH(R)—] —. Diisotactic and disyndiotactic erythro and threo polymers only one of the enantiomorphic forms of the polymers is shown...

A study on the homo- and copolymerization of a variety of dienes such as 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, E-l,3-pentadiene, E-l,3-hexadiene, E-l,3-heptadiene, E-l,3-octadiene, E,E-2,4-hexadiene, E-2-methyl-l,3-pentadiene, 1,3-cyclohexadiene mainly focused on mechanistic aspects [139]. It was shown that 1,4-disubstituted butadienes yield frans-1,4-polymers, whereas 2,3-disubstituted butadienes mainly resulted in cis- 1,4-polymers. Polymers obtained by the polymerization of 1,3-disubstituted butadienes showed a mixed trans-1,4/cis-1,4 structure (60/40). The microstructures of the investigated polymers are summarized in Table 26. 

Tellurophene is decomposed by strong mineral acids. Tetrachlorotellurophene Te,Te-dichloride is rapidly converted by aqueous base to l,2,3,4-tetrachloro-l,3-butadiene and tellurous acid s. 2,5-Diphenyltellurophene reacted with butyl lithium in hexane in the presence of tetramethylethylenediamine at 20" to give l,4-dilithio-l,4-diphenyl-l,3-butadicne, a compound that can be used as a starting material for the synthesis of 1,4-disubstituted butadienes . 

Photooxidation of ( , )-1,4-disubstituted butadienes produces the corresponding 3,6-dihydro-1,2-dioxines 465 that are dihydroxylated into diols 466. Upon reduction (Zn/AcOH, or H2/Pd-C, or H2/Pt-C Mg/l2 (cat.), or thioureas) racemic alditols 467 are obtained. Isomerization of the dioxines catalyzed by iVA -bis(salicylidene)ethylenedianiinocobalt (II) gives the corresponding racemic uloses 468 (O Scheme 109). The method has been used to prepare ( )-psicose, ( )-l-deoxypsicose ( )-6-deoxypsicose [551]. 

Tanaka, T. and Matsumoto, A. (2002) First disyndiotactic polymer from a 1,4-disubstituted butadiene by alternate molecular stacking in the crystalline state. J. Am. Chem. Soc., 124, 9676-9677. 

Solid-State Polymerization of 1,4-Disubstituted Butadienes in Layered Structures... 

Since polymerization in inclusion compounds is restricted to only a few monomers with small substituent groups, it seemed worthwhile to search for other systems where butadiene derivatives are able to polymerize exclusively according to a 1,4-addition mechanism. In the following, our recent investigations (JJl-ii.) on the polymerization behavior of 1,4-disubstituted butadienes in various layered structures will be reviewed. Polymerization has been investigated... 

The coupling of arylzinc halides w ith i 3-Arylindoles are obtained from 3-indols 1.4-disubstituted butadienes - starts from i After Pd(0)-catalyzed coupling with alke Grignard reaction in the presence of 1 Ph. P... 

Polymerization of 1,4-disubstituted butadienes can lead to products that possess two asymmetric carbon atoms and one double bond in each repeat unit. Such tritactic polymers are named with prefixes of cis or trans together with erythro or threo (see Fig. 1.13). 

In principle, 1,4-disubstituted butadienes can give different types of 1,4-stereoregular polymers erythro (or threo) trans-1,4 iso- or syndiotactic. 

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