Dienes/alcohols, telomerization

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. 

The telomerization of dienes in a two-phase system was first described in a patent (100). Water was used as the solvent for the catalyst, with sulfonated phosphane ligands providing the water solubility. Water, alcohols, phenols, acids, amines, and acetylacetic add were used as nucleophiles. 

Jackstell R, Andreu MG, Frisch A, Selvakumar K, Zapf A, Klein H, Spannenberg A, Rottger D, Briel O, Karch R, Beller M (2002) A highly efficient catalyst for the telomerization of 1,3-dienes with alcohols first synthesis of a monocarbenepalladium(0)-olefin complex. Angew Chem Int Ed 41 986-989... 

Although the telomerization of dienes in a two-phase system has been intensively investigated with compounds containing active hydrogen such as alcohols, amines, phenols, acids, etc., the selective and productive telomerization of butadiene continues to be a challenge. It is only recently that primary octadi-enylamines have been obtained with selectivity up to 88% in the telomerization of butadiene with ammonia using a two-phase toluene/water system and Pd(OAc)2/tppts as the catalyst [Eq. (23)] [125]. 

The linear telomerization reaction [1] of dienes (the taxogen) with nucleophiles (the telogen) such as alcohols, amines, carboxylic acids, active methylene compounds, phenols, or water provides an elegant method for the synthesis of various useful compounds (Eq. 1). 

Telomerization is defined as an oligomerization of dienes accompanied by addition of a heteroatom or carbon nucleophilic reagent10. It is catalyzed by various organometallic compounds of transition metals, especially palladium compounds. The nucleophiles, such as water, alcohols, amines or carboxylic acids, as well as enamines, nitroalkanes and stabilized carban-ions, are mainly introduced in the terminal position of the dimeric molecule in excellent yield10. It is also possible to direct the reaction towards an internal product functionalization. Telo-merizations with heteronucleophiles are regarded as heterocarborative addition reactions and are described in Section 1.5.8.4. 

Telomerization reactions, the formation of short oligomers from dienes, represent a very efficient organic transformation with an overall atom economy of 100%, and they have been the subject of intensive research in both academic and industrial laboratories. Complexes of palladium are known to catalyze the reaction of dienes with a variety of nucleophiles. Mechanistically, the reactions are thought to proceed by allyl coordination of two butadiene molecules to a palladium(O) center followed by the formation of a C-C bond. The eight-carbon chain is then attacked by a nucleophile at the terminal or at the 3 position. The reaction usnally leads to a mixture of cis/trans isomers and n- and iio-prodncts. When the nncleophile is methanol, l-methoxyocta-2,7-diene 1 (n-product) is generally the major prodnct, which is a nseful precnrsor for plasticizer alcohols (octanols), solvents, corrosion inhibitors, and monomers for polymerization. ... 

The telomerization of dienes with alcohols as the nucleophile has now been conducted in a practical fashion. A palladium catalyst containing an N-heterocyclic carbene ligand has been shown to form linear dimeric ethers selectively from alcohols and butadiene with remarkably high turnover numbers (Equation 22.40). The activity of this catalyst is significantly higher than that of the more classical catalysts generated from Pd(OAc)j and PPhj. Under optimized conditions involving some added carbene precursor, presumably to... 

Aqueous and aqueous-organic biphasic systems would constitute straightforward reaction mixtures for catalyzed hydration of olefins and alkynes. In fact, water is chemically utilized in telomerization of dienes with H2O (179) and hydration of alkynes has also gained synthetic importance (222). However, these reactions are usually run in homogeneous solutions making the olefin or alkyne soluble by using a water-miscible organic cosolvent (alcohols, THF). 

In what follows, the telomerization of butadiene with acetic acid, alcohols, phenol, C—H-acidic compounds and nitroalkanes will be considered. Also some examples of carboxytelomerization and the telomerization of substituted dienes will be given. In all reactions trifunctional compounds are formed which contain two double bonds and one functional group. 

TelomerizatiorL Conj ugated dienes combine with nucleophiles such as water, amines, alcohols, enamines and stabilized carban-ions in the presence of palladium acetate and triphenylphosphine to produce dimers with incorporation of one equivalent of the nucleophile. Telomerization of butadiene (eq 7) yields linear 1,6- and 1,7-dienes and has been used for the synthesis of a variety of naturally occurring materials. ... 

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