Carboxylation of conjugated dienes

However, most studies have dealt with Ni(0)-based systems [1-10, 48, 98-102]. The reactivity of conjugated dienes with Ni(0)-complexes and carbon dioxide is higher than that exhibited by monoenes. Accordingly, the reaction of Ni(bpy) (cod) with CO2 and 1,3,7-octatriene yielded products which indicate that CO2 attacks only at the diene moiety of octatriene [101]. 

In the presence of transition metal (Pd, Ni, Ru, Rh) catalysts, conjugated dienes can also coohgomerize with carbon dioxide. The first studies on catalytic cooligomerization of 1,3-dienes with CO2 date back to the end of the 1970s and 

The first step is butadiene dimerization by oxidative coupling of two diene molecules to give a bis-tj -allylpalladium complex A which may exist in equilibrium with the isomer A. Direct coupling of CO2 with a diene molecule is not a 

The cooligomerization process can also be promoted by Rh catalysts [108, 115]. However, in the presence of neutral or ionic complexes of Rh(l) or Rh(lll) as catalyst precursors (for instance, the system (C2H4)2Rh(acac)/PEt3), y-lactone 2-ethyl-2,4,9-undecatriene-4-olide (6) was isolated, in 

Moss JR (1999) Recent developments in the activation of carbon dioxide by metal complexes. Coord Chem Rev 181 27-59 

---

The chloroacetoxylation is a quite general reaction and works well with a number of conjugated dienes. Some additional examples are given in Scheme 6 and in equations 15 and 16. The reaction is highly syn stereoselective for a number of cyclic dienes tried. Also, for acyclic dienes the reaction leads to a 1,4 syn addition and the reaction takes place with good stereospecificity (94 -96% syn). Thus (Zi,.E)-dienes give the R R isomer whereas (E,Z)-dienes produce the R S isomer (equations 15 and 16). The reaction has also been extended to include other carboxylic acids than acetic acid (chloroacyloxylation)33d. 

The course of hydrocarboxylation was studied further by sequential analyses of reaction mixtures and by detailed characterization of the purified carboxy acid products. Figure 1 plots kinetic runs with linoleic acid and methyl linoleate at 120°C. Analysis by GLC shows the rapid disappearance of diene followed successively by initial conjugation of the diene system, monocarboxylation, and then dicarboxylation. Cyclic ketones and other unidentified materials (not shown) are formed in minor amounts. Conjugated dienes (mixture of cis,trans and trans,trans) peak at 1 hr and then rapidly disappear. Monocarboxy acids peak around 6-8 hrs and disappear at later stages of the reaction. At 140°C, the carboxylation follows the same course (Figure 2A). Formation of conjugated dienes reach a maximum around 0.5 hr. Monocarboxy acids peak around 1 hr, decrease, and then level at 3-4 hrs. 

Catalytic carboxylation of cis,trans conjugated linoleate is accompanied by initial thermal isomerization to trans,trans-conjugated dienes which reach a peak concentration around 1 hr (Figure 2B). A small but significant amount of nonconjugated diene reaches a maximum of 3% around 4 hrs. Mono- and dicarboxylation of conjugated dienes follow... 

The hydrocarboxylation of conjugated dienes such as butadiene can yield monocarboxylate, dicarbox-ylate or diene dimerized carboxylated products. The carboxylation reaction is important because it is a potential route to adipic acid. 

Sulfonylmercuration of conjugated dienes occurs using PhSOjNa and HgClj. (vii) Intramolecular Nucleophiles. Suitably placed hydroxyl, amine and carboxyl groups in the alkene can act as the nucleophile and give rise to cyclic products. Five-membered rings frequently are formed, e.g. ... 

Epoxidations. Further utilities for the dioxirane derived from fructose is the regio-and enantioselective epoxidation of conjugated dienes and enynes. Continuing explorations of the (salen)manganese(III) systems have uncovered the catalyzed epoxidation of 2-sulfonyl-1,3-dienes at the nondeactivated sites, and the advantage of added carboxylate salt as cocatalyst. ... 

Allylic bromination by NBS can be applied with success not only to olefins but also to <%,/ -unsaturated ketones, carboxylic esters, nitriles, and lactones. Radical-formers must be added when NBS is used for allylic bromination of conjugated dienes, for side-chain bromination of aromatic or heterocyclic compounds (see p. 198), or for replacement of tertiary hydrogen atoms next to a C=C bond. 

Co-Oligomerization of Diels-Alder Adducts of Conjugated Dienes with Filodienes That Contain Carboxylic Groups... 

The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyl-7-laCtone 4I9[380], The /i,7-titisaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

Conjugated dienes give 1,4 addition. This reaction has also been performed with salts of carboxylic acids in what amounts to a method of alkylation of carboxylic acids (see also 10-96). ... 

In the case of carboxylic acids [33], ketones [47] or sulfones [49], it was possible to prove a further prototropic rearrangement of allenes 19 with R2 = H yielding the alkynes 20. In other examples, the prototropic isomerization of the triple bond leads to conjugated dienes directly thus the allene of type 19 could only be postulated as an intermediate [50]. Braverman et al. showed that the allenes generated by prototropic isomerization of dipropargylic sulfones or sulfoxides, for example 24, are unstable. They are transferred rapidly via diradical intermediates to polycycles such as 27 [51-53],... 

---