Diene coupling

The linear telomerization reaction of dienes was one of the very first processes catalyzed by water soluble phosphine complexes in aqueous media [7,8]. The reaction itself is the dimerization of a diene coupled with a simultaneous nucleophilic addition of HX (water, alcohols, amines, carboxylic acids, active methylene compounds, etc.) (Scheme 7.3). It is catalyzed by nickel- and palladium complexes of which palladium catalysts are substantially more active. In organic solutions [Pd(OAc)2] + PPhs gives the simplest catalyst combination and Ni/IPPTS and Pd/TPPTS were suggested for mnning the telomerizations in aqueous/organic biphasic systems [7]. An aqueous solvent would seem a straightforward choice for telomerization of dienes with water (the so-called hydrodimerization). In fact, the possibility of separation of the products and the catalyst without a need for distillation is a more important reason in this case, too. 

Some homogeneously catalyzed telomerizations, i.e., dimerizations of dienes coupled with the addition of a nucleophile [Eq. (11)], have been carried out in two-phase systems. One example has found industrial application, the synthesis of 1,7-octadienol from butadiene and water (Section VI). 

The modified Negishi protocoi was used in J.S. Panek s total synthesis of (-)-motuporin to couple the left-hand subunit organozinc compound with the right-hand subunit ( )-vinyl iodide. The left-hand subunit was prepared by the Schwartz hydrozirconation of a disubstituted alkyne to give an ( )-trisubstituted zirconate, which was subsequently transmetalated with anhydrous ZnCl2. The resulting vinylzinc species was immediately treated with one equivalent of the ( )-vinyl iodide in the presence of 5 mol% Pd(PPhs)4 to afford the ( , )-diene coupled product with complete stereoselectivity. 

Dienes. Coupling of allylamines with alkenylboronic acids with (PhjPl Ni in benzene leads to 1,4-dienes. 

Vanadium catalysis mostly by cationic diene coupling metallocene by end group copolymerization can be controlled (information available from manufacturers)... 

B.ii. Intramolecular Diene Coupling of Alkyl-Substituted Dienes ... 

B.iv. Intramolecular Diene Coupling Influence of Ester Substituents... 

The intramolecular diene coupling with trapping by sulfinic acid has also been shown to be viableBisdiene 117 is trapped by p-toluenesulfinic acid (0.05 [Pd(OAc>2/2 PhjP], benzene, 70 °C) to afford allylic sulfone 118 in moderate yield (50%, 13 1 trans/cis ring substitution). 

C.xi. Doubly Activated Methylene and Methines (C—H Acidic Compounds) as the H—Y Trapping Reagent Inter- and Intramolecular Diene Coupling... 

E.iii. Aldehydes and Ketones as TVapping Agents Intramolecular Diene Coupling... 

To select the ideal A, chromophore units of a particular compound need to be well recognized, such as conjugated dienes coupled to an acid group and respec-... 

The telomerization reactions are thought to occur by the mechanism in Scheme 22.20. In this mechanism, the two dienes couple to form the tethered alkyl allyl complex. The isolation of this class of complex was reported by Jolly and Wilke during mechanistic studies of diene oligomerization and later by others. Reaction of this complex with methanol would then protonate the olefinic C-3 carbon, and the resulting methoxide would attack the terminal position of the coordinated allyl to generate the resulting diene complex. Replacement of the dienyl ether ligand by two equivalents of butadiene restarts the catalytic process. 

Scheme P12.13.3 Synthesis of multi-diene coupling agents carrying 2, 3, and 4 diene groups. (Drawn following the synthesis method of Inglis et al., 2008.)...

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