Butadiene, catalyzed reactions telomerization

In addition to the applications reported in detail above, a number of other transition metal-catalyzed reactions in ionic liquids have been carried out with some success in recent years, illustrating the broad versatility of the methodology. Butadiene telomerization [34], olefin metathesis [110], carbonylation [111], allylic alkylation [112] and substitution [113], and Trost-Tsuji-coupling [114] are other examples of high value for synthetic chemists. 

The most characteristic reaction of butadiene catalyzed by palladium catalysts is the dimerization with incorporation of various nucleophiles [Eq. (11)]. The main product of this telomerization reaction is the 8-substituted 1,6-octadiene, 17. Also, 3-substituted 1,7-octadiene, 18, is formed as a minor product. So far, the following nucleophiles are known to react with butadiene to form corresponding telomers water, carboxylic acids, primary and secondary alcohols, phenols, ammonia, primary and secondary amines, enamines, active methylene compounds activated by two electron-attracting groups, and nitroalkanes. Some of these nucleophiles are known to react oxidatively with simple olefins in the presence of Pd2+ salts. Carbon monoxide and hydrosilanes also take part in the telomerization. The telomerization reactions are surveyed based on the classification by the nucleophiles. 

Vollmuller F, Magerlein W, Klein S, Krause J, Beller M (2001) Palladium-catalyzed reactions for the synthesis of fine chemicals, 16 - highly efficient palladium-catalyzed telomerization of butadiene with methanol. Adv Synth Catal 343 29-33... 

Dienes, especially butadiene, also react with carbon dioxide. Inotie and his co-workeis found that Pd(dppe)j catalyzes the telomerization of butadiene and CO to give the y-lactone 2 Cthylidcnc-5 hcpien-4-oUde in about a S% yield [182, 183]. The distribution of the products evidently depends on the solvent used and polar aproiic solvents such as DMF, DMSOand 1 mielhyl-2-pyrrolidone are most suitable for lactone formation. A temperature of 120 C is required. When the reaction is carried out at temperatures below lOO C and terminated before the complete conwrsion of butadiene, the free organic acids (the precursors of the >4actone) are isolated up to 10%. 

If ILs are to be used in metal-catalyzed reactions, imidazoHum-based salts may be critical due to the possible formation and involvement of heterocyclic imidazo-lylidene carbenes [Eqs. (2)-(4)]. The direct formation of carbene-metal complexes from imidazolium ILs has already been demonstrated for palladium-catalyzed C-C reactions [40, 41]. Different pathways for the formation of metal carbenes from imidazolium salts are possible either by direct oxidative addition of imidazolium to the metal center in a low oxidative state [Eq. (2)] or by deprotonation of the imidazolium cation in presence of a base [Eq. (3)]. It is worth mentioning here that deprotonation can also occur on the 4-position of the imidazolium [Eq. (4)]. The in-situ formation of a metal carbene can have a beneficial effect on catalytic performances in stabilizing the metal-catalyst complex (it can avoid formation of palladium black, for example). However, given the remarkable stability of this imidazolylidene-metal bond with respect to dissociation, the formation of such a complex may also lead to deactivation of the catalyst This is probably what happens in the telomerization of butadiene with methanol catalyzed by palladium-phosphine complexes in [BMIMj-based ILs [42]. The substitution of the acidic hydrogen in the 2-position of the imidazolium by a methyl group or the use of pyridinium-based salts makes it possible to overcome this problem. Phosphonium-based ILs can also bring advantages in this case. 

The palladium(O)-catalyzed reaction of 1,3-dienes with active methylene compounds to give 1,4-addition of a hydrogen atom and a stabilized carbanion is complicated by the formation of 2 1 telomerization products [27]. It was found by Hata et al. [21a] that bidentate phosphines such as l,2-(diphenylphosphino)ethane favor formation of the 1 1 adduct. More recent studies by Jolly have shown that the use of more a-donating bidentate phosphines on palladium gave a high selectivity for 1 1 adducts [23]. For example, 1,3-butadiene reacted with 11 to give the 1,4-addition product 12 in 82% yield, along with 18% of the 1,2-addition product 13 (Eq. (7)). 

Coupling of butadiene with CO2 under electrochemically reducing conditions produces decadienedioic acid, and pentenoic acid, as weU as hexenedioic acid (192). A review article on diene telomerization reactions catalyzed by transition metal catalysts has been pubUshed (193). 

When the products are partially or totally miscible in the ionic phase, separation is much more complicated (Table 5.3-2, cases c-e). One advantageous option can be to perform the reaction in one single phase, thus avoiding diffusional limitation, and to separate the products in a further step by extraction. Such technology has already been demonstrated for aqueous biphasic systems. This is the case for the palladium-catalyzed telomerization of butadiene with water, developed by Kuraray, which uses a sulfolane/water mixture as the solvent [17]. The products are soluble in water, which is also the nucleophile. The high-boiling by-products are extracted with a solvent (such as hexane) that is immiscible in the polar phase. This method... 

Extension to carbocyclization of butadiene telomerization using nitromethane as a trapping reagent is reported (Eq. 5.48).72 Palladium-catalyzed carbo-annulation of 1,3-dienes by aryl halides is also reported (Eq. 5.49).73 The nitro group is removed by radical denitration (see Section 7.2), or the nitroalkyl group is transformed into the carbonyl group via the Nef reaction (see Section 6.1). 

These telomerization reactions of butadiene with nucleophiles are also catalyzed by nickel complexes. For example, amines (18-23), active methylene compounds (23, 24), alcohols (25, 26), and phenol (27) react with butadiene. However, the selectivity and catalytic activity of nickel catalysts are lower than those of palladium catalysts. In addition, a mixture of monomeric and dimeric telomers is usually formed with nickel catalysts ... 

To prepare more hydrophobic starches for specific applications, the partial substitution of starch with acetate, hydroxypropyl, alkylsiliconate or fatty-acid ester groups has been described in the literature. A new route, however, consists of grafting octadienyl chains by butadiene telomerization (Scheme 3.9) [79, 82, 83], The reaction was catalyzed by hydrosoluble palladium-catalytic systems prepared from palladium diacetate and trisodium tris(m-sulfonatophenyl)phosphine (TPPTS). 

Solutions of the nickel(O) and palladium(O) complexes of 1,3,5-triaza-7-phosphaadamantane, PTA (82) and tris(hydroxymethyl)phosphine (98) in water catalyze the oligomerization and telomerization of 1,3-butadiene at 80 °C. Although high yields and good selectivities to octadienyl products (87 %) were obtained, the complexes (or the intermediate species formed in the reaction) dissolve sufficiently in the organic phase ofthe monomer and the products to cause substantial metal leaching [17],... 

The catalyzed telomerization of butadiene has been applied to other polysaccharides such as inulin (22) (Fig. 20) which is a polyfructose extracted from Jerusalem artichokes (tuber) or from chicory (roots). This soluble polymer is easily telomerized under mild conditions and the degree of substimtion is also dependent on the reaction conditions [20] (Fig. 20). 

Other Alkyl Ethers. Sucrose has been selectively etherified by electrochemical means to generate a sucrose anion followed by reaction with an alkyl halide (21,22). The benzylation of sucrose using this technique gives 2-O-benzyl- (49%), T-O-benzyl- (41%), and 3 -O-benzyl- (10%) sucrose (22). The benzylation of sucrose with benzyl bromide and silver oxide in DMF also produces the 2-O-benzyl ether as the principal product, but smaller proportions of T- and 3 -ethers (23). Octadienyl ether derivatives of sucrose, intermediates for polymers, have been prepared by a palladium-catalyzed telomerization reaction with butadiene in 2-propanol—water (24). 

Alkyl ethers of sucrose have been prepared by reaction with long-chain alkyl halides to provide mixtures of regioisomers and products of different degree of substitution.82,83 A similar reaction with chloromethyl ethers of fatty alcohols provides formaldehyde acetals.84,85 Alkenyl ethers of various carbohydrates, and notably of sucrose, can also be obtained by palladium-catalyzed telomerization of butadiene (Scheme 6).86 88 Despite a low-selectivity control, this simple and clean alternative to other reactions can be carried out in aqueous medium when sulfonated phosphines are used as water-soluble ligands. 

Telomerization with various nucleophiles affords interesting functionalized dimers 133 and 134 [50-54]. The Pd-catalyzed telomerizations of butadiene with various nucleophles gives 1-substituted 2,7-octadienes 133 as major products, and 3-substituted 1,7-octadienes 134 as minor products as summarized in Scheme 5.1. The telomers obtained by the Pd-catalysed reactions are useful building blocks. Natural products, such as steroids and macrolides, are synthesized efficiently using these telomers [55]. 

Abstract The dimerization of 1,3-dienes (e.g. butadiene) with the addition of a protic nucleophile (e.g. methanol) yields 2,7-octadienyl ethers in the so-called telomerization reaction. This reaction is most efficiently catalyzed by homogeneous palladium complexes. The field has experienced a renaissance in recent years as many of the platform molecules that can be renewably obtained from biomass are well-suited to act as multifunctional nucleophiles in this reaction. In addition, the process adheres to many of the principles of green chemistry, given that the reaction is 100% atom efficient and produces little waste. The telomerization reaction thus provides a versatile route for the production of valuable bulk and specialty chemicals that are (at least partly) green and renewable. The use of various multifunctional substrates that can be obtained from biomass is covered in this review, as well as mechanistic aspects of the telomerization reaction. 

Scheme 1 Generalized reaction scheme for the Pd-catalyzed telomerization of 1,3-butadiene with nucleophile NuH...

Prinz T, Driessen-Holscher B (1999) Biphasic catalyzed telomerization of butadiene and ammonia kinetics and new ligands for regioselective reactions. Chem Eur J 5 2069-2076... 

Musco A, Perego C, Tartiari V (1978) Telomerization reactions of butadiene and C02 catalyzed by phosphine Pd(0) complexes - (E)-2-ethylidenehept-6-en-5-olide and octadienyl esters of 2-ethylidenehepta-4,6-dienoic acid. Inorg Chim Acta 28 L147-L148... 

The preparation of different (NHC) - Pd°(dvds) complexes allowed the authors to make a systematic comparison of structure/activity for the telomerization reaction [228]. This study showed that electron-withdrawing substituents on the carbene backbone destabilizes the catalyst and therefore enhance its reactivity. These catalysts are applicable to primary and secondary alcohol as well as phenols and represent the first industrially viable catalyst system for palladium-catalyzed telomerization of butadiene with alcohol. 

Butadiene as raw material is available in high amounts from the C4 fraction of raffmation processes. The telomerization of butadiene itself catalyzed by different metal catalysts is a well documented reaction. Depending on the catalyst and on the conditions different telomeres may be synthesized. Carrying out the reaction under carbon dioxide instead of argon atmosphere, 1,3,7-octatriene becomes the main product Pioneering work of Inoue and co-workers in 1976 showed that the same reaction under carbon dioxide atmosphere lead to co-oligomeres 2, 5 and 6 when palladium complexes are used as catalysts (Scheme 1). 

It deserves mention that related palladium-catalyzed C-C coupling cascades have been combined with a carbonylation terminating step [41]. In such cases vinyl-, alkyl- or allylpalladium(II) intermediates were generated in situ and trapped by carbonylation reactions, mainly carboxylations. As an example pelar-gonic (nonanoic) acid, an industrially interesting synthetic fatty acid, has been prepared via butadiene telomerization in the presence of methanol, subsequent carbonylation of the resulting allylic ethers and hydrogenation (eqs. (13) and (14)) [42]. 

Butadiene is a very inexpensive and attractive molecule for the industrial chemist. Several products can be made from butadiene and carbon monoxide under specific conditions. Subtle effects control the outcome of palladium-catalyzed carboxyla-tion of conjugated dienes such as butadiene. Depending on the reaction conditions, monocarboxylate, dicarboxylate, or telomerized products could be obtained (Scheme 4, cf. Section 2.3.5). 

The key reaction of this 1-octanol process is telomerization of butadiene with a palladium complex catalyst. Known attempts to commercialize the palladium complex-catalyzed telomerization have failed, in spite of great efforts, for the following reasons (1) palladium complex catalysts are thermally unstable and tbe catalytic activity markedly decreases when, as a means of increasing the thermal stability, the ligand concentration is increased (2) a sufficiently high reaction rate to satisfy industrial needs cannot be obtained (3) low selectivity and (4) distillative separation of reaction products and unreacted butadiene from the reaction mixture causes polymeric products to form and the palladium complex to metallize. Kuraray succeeded in 1991 in commercializing the production of 1-octanol using hydrodimerization of butadiene. 

The Pd-catalyzed dimerization of butadiene in the presence of water yields octa-dienols (cf. Section 2.3.5). This type of reaction is referred to as telomerization and can be performed with high selectivity for 2,6-octadien-l-ol in ionic liquids like 1 leaving the product separated from the reaction medium [35]. 

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