Conjugated dienes stereoisomers

Another reaction unique to conjugated dienes is the Diels-Alder cycloaddition. Conjugated dienes react with electron-poor aikenes (dienophiles) in a single step through a cyclic transition slate to yield a cyclohexene product. The reaction is stereospecific, meaning that only a single product stereoisomer is formed, and can occur only if the diene is able to adopt an s-cis conformation. 

Dienes. Hydrosilylation of conjugated dienes often leads to a complex mixture of products composed of regio- and stereoisomers of 1 1 addition, 1 2 addition products, and oligomers. Dihydrosilanes may form silacycloalkanes as well. In contrast... 

A-2. Provide the IUPAC name for each of the conjugated dienes of the previous problem, including stereoisomers. 

Conjugated dienes are much less common in cuticular lipids, and there are a large number of ways in which any desired isomer can be made with high stereoselectivity. The interested reader is referred to the compilation of methods in Mori (1992) as a starting point. A convenient route to any one or all four stereoisomers of a conjugated diene from two acetylenic precursors has been described by Svatos and Saman (1997). 

As regards polymers of other conjugated dienes (higher alkyl 1,4-disubsti-tuted 1,3-butadienes), it has already been mentioned that several stereoisomers of such polymers have been obtained [7]. 

Selenium electrophiles add to conjugated dienes, only forming 1,2-adducts. Although Maricovnikov addition is seen, only a few examples have been reported. With allenes the additions are re ospeciric, with the i enylseleno group usually adding to the rp-carbon. Unfortunately, all four stereoisomers of halide attadc are seen with unsymmetrically substituted allenes. ... 

A variety of other conjugated dienes participate in the [4 + 1] annulation with stereochemistry in accord with the predictions of equation (20). The 1-vinylcycloalkenes (87)-<89) can be viewed as ( )-sub-stituted dienes, and are thus expected to yield the exo-alcohols (90)-<92). In each of these cases carbene addition generates a mixture of four intermediate 2-vinylcyclopropyl ethers, each of which then rearranges to produce exclusively the predicted stereoisomer. Application of the annulation to the endocyclic (Z,Z)-dienes (93) and (94) also generates in each case a single bicyclo[/i.2.1]alkenol, and the ( , )-diene (97) similarly reacts to afford exclusively the cyclopentenol (98 Scheme 7). 

Following is an outline of a synthesis of bombykol, the sex attractant of the male silkworm moth. Of the four stereoisomers possible for this conjugated diene, the 10-trans-12-cis isomer shown here is over 10 times more potent as a sex attractant than any of the other three possible stereoisomers. 

The polymer name may consist of as many as four parts (1) the primary source material, under which the polymer is indexed (2) the functional type, that is, the type of functionality incorporated into the backbone (3) the co-reagent and (4) the structure designation. The structure designation is necessary because more than one mode of polymer formation may be possible from the same source materials. Structural isomers, geometrical isomers, and stereoisomers must be differentiated, as well as structures which are not isomeric. The different polymer structures which may be formed in the polymerizations of conjugated dienes are designated as shown in the case of 1,3-butadiene ... 

Unlike allenes, conjugated dienes are inert toward hydrophosphinylation except for isoprene and its analogues (Scheme 58). Nonconjugated a,oo-dienes react selectively at one of the terminal C=C bonds forming a linear product. Enyne compounds react at the C=C bond selectively although they furnish unselective mixtures of regio- and stereoisomers. 

Two years later, the transformation of the isoprene dimer (91) to (94) (mixture of stereoisomers) was observed and interpreted as a conjugate addition of Bu"Li to diene (91) followed by a (surprisingly smooth) intramolecular lithium-ene addition (92) (93) (Scheme 21). ... 

Rate data are also reported for the base hydrolysis of three stereoisomers of the [Co(dien)(tmd)Cl] + ion and one isomer of [Co(dpt)(tmd)CI]2+ [structures (12)— (15)]. The results are compared with previous data in Table 24. Complexes with structures (13) and (15) in which the triamine is in a meridional position react 10 — 10 times faster than those in which the triamine is facial. Deprotonation of the secondary amine (NH) groups is indicated for these conjugate-base reactions. 

The direct complexation of 1,4-dienes can form specific stereoisomers. Initial -ir-complexation occurs before the conjugation step, and the hydrogen atom moves only on the face of the ligand carrying the metal. Unfortunately, a mixture of regioi-somers usually results, which may present separation problems. Loss of OMe can also sometimes occur, particularly from some l,3-dimethoxy-l,4-cyclohexadienes. In these cases, preconjugation of the diene is essential if a dimethoxydiene complex is required. Mixtures of complexes obtained from 1,4-dienes may also be equilibrated to thermodynamic ratios of isomeric complexes, which do not correspond to the equilibrium ratios of the free dienes. ... 

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