Butadienyl anions

Desoxyleukotriene D4 was synthesized to determine whether the 5-hydroxyl group is necessary for biological activity. It is, since the bioactivity of 5-desoxyleukotriene D4 is less than % that of LTD4 itself. An interesting synthetic equivalent of the 4-formyl- , -l,3-butadienyl anion was utilized in the synthesis. 

In ionic polymerizations, the polarity of the monomers or the ions is far more important than resonance stabilization, while in free radical copolymerizations the reverse is true. For example, if > r2 in cationic copolymerization, then, by contrast, in anionic copolymerization r2 (Table 22-13). If the polarities are very different, then it is no longer possible to have either cationic or anionic copolymerization. The styryl anion, for example, still adds butadiene, but the butadienyl anion does not add styrene. Only monomers with almost identical polarity can undergo true copolymerizations (with r r2 < 1) unless complexes are formed between the active growing end and the monomer. 

Scheme 13.39 Use of the 1-formyl butadienyl anion equivalent in the total synthesis of ( )-asteltoxin. ... 

Studies of the copolymerizations of 1,1-diphenylethylene and dienes showed rather different behavior compared with the copolymerizations of styrene and 1,1-diphenylethylene [125, 133-136]. The monomer reactivity ratios for copolymerizations of dienes with DPE are shown in Table 7. When butadiene was copolymerized with 1,1-diphenylethylene in benzene at 40 °C with -butyl-lithium as initiator, the monomer reactivity ratio for butadiene, ri, was 54 this means that the addition of butadiene to the butadienyl anion is 54 times faster than addition of 1,1-diphenylethylene to the butadienyl anion [133]. This unreactivity of poly(butadienyl)lithium towards addition to DPE was also observed in studies of end-capping of poly(butadienyl)lithium with DPE in hydrocarbon solution (see Sect.3.3) [109, 111]. Because of this unfavorable monomer reactivity ratio, few DPE units would be incorporated into the co-... 

When a mixture of styrene and 1,3-butadiene (or isoprene) undergoes lithium-initiated anionic polymerization in hydrocarbon solution, the diene polymerizes first. It is unexpected, since styrene when polymerized alone, is more reactive than, for example, 1,3-butadiene. The explanation is based on the differences of the rates of the four possible propagation reactions the rate of the reaction of the styryl chain end with butadiene (crossover rate) is much faster than the those of the other three reactions484,485 (styryl with styrene, butadienyl with butadiene or styrene). This means that the styryl chain end reacts preferentially with butadiene. 

Morton et al.135,141) were the first to study the poly(butadienyl)lithium anionic chain end using (b). They found no evidence of 1,2-chain ends and concluded that only 1,4-structures having the lithium cr-bonded to the terminal carbon were present. A later study by Bywater et al.196), employing 1,1,3,4-tetradeuterobutadiene to minimize the complexity of the spectrum that arises from proton-proton coupling, found that the 1 1 adduct with d-9 fert-butyllithium in benzene exists as a mixture of the cis and trans conformers in the ratio 2.6 1. Glaze et al. 36) obtained a highly resolved spectrum of neopentylallyllithium in toluene and found a cis trans ratio of about 3 1. 

This type of halogenation procedure involving active centers should be carefully examined since like a,a -dibromoxylene it is applicable to unsaturated polymeric anions such as poly(butadienyl)lithium and poly(isoprenyl)lithium whose double bonds would react directly with halogens. 

A series of organic salts, comprising an alkylated pyridinium ion linked to a dimethylamino group by a n-system and an inorganic anion, have recently been used as spectroscopic probes of dimethylacrylate photopolymerization [112], An example is 2-[4-(4-(dimethylamino)phenyl)-l,3-butadienyl]-l-... 

Chiral Auxiliary for Asymmetric Induction. Numerous derivatives of (—)-8-phenylmenthol have been utilized for asymmetric induction studies. These include inter- and intramolecular Diels-Alder reactions, dihydroxylations, and intramolecular ene reactions of a,p-unsaturated 8-phenylmenthol esters. These reactions usually proceed in moderate to good yield with high diastereofacial selectivity. a-Keto esters of 8-phenylmenthol (see 8-Phenylmenthyl Pyruvate) have been used for asymmetric addition to the keto group, as well as for asymmetric [2 -F 2] photoadditions and nucleophilic alkylation. Ene reactions of a-imino esters of 8-phenylmenthol with alkenes provide a direct route to a-amino acids of high optical purity. Vinyl and butadienyl ethers of 8-phenylmenthol have been prepared and the diastereofacial selectivity of nitrone and Diels-Alder cycloadditions, respectively, have been evaluated. a-Anions of 8-phenylmenthol esters also show significant diastereofacial selectivity in aldol condensations and enantiose-lective alkene formation by reaction of achiral ketones with 8-phenylmenthyl phosphonoacetate gives de up to 90%. ... 

Morton et al. were the first to study the poly(butadienyl)lithium anionic... 

The initial stage involves the formation of a highly reactive anion Fe(CO)4 , which interacts with isolated double bonds, followed by double bond isomerization and the formation of n-complexes with the iron tricarbonyl residues. The final product is composed of the ri" -(butadienyl)irontricarbonyl units with both trans-trans- and cis-trans-tetramethylene groups. Since the iron tricarbonyl complexes with two noncon-jugated double bonds are unstable, no complexes between two polymer chains are formed. The reaction of iron carbonyls with low-molecular-weight nonconjugated dienes is accompanied by the double bond migration. 

Butadienyl sulphoxides act as excellent Michael acceptors for nucleophilic acylating agents, particularly lithiated cyanohydrin ethers." The resulting allylic anions may be alkylated, and simple hydrolyses complete an efficient synthesis of dienones [equation (30)]. 

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