Heck reaction in aqueous media

Heck reaction in aqueous media Jeffery. T. Tetrahedron Utt., 1994, 35, 3051... 

Several intramolecular Heck reactions in aqueous media have been published (Scheme though no systematic investigation on the possible effects of water... 

The development of a Heck reaction in aqueous media, enabling a one-pot process with both reaction steps (Heck reaction and biotransformation) running in aqueous media, was also reported by Cacchi and coworkers [65]. This type of Heck reaction is based on the use of a phosphine-free perfluoro-tagged palladium nanoparticle. After detailed catalyst characterization and process development, Cacchi and coworkers also succeeded in combining this Heck reaction efficiently with the subsequent asymmetric ketone reduction toward a one-pot process. A representative example is shown in Scheme 19.25. The enzymatic process turned out to be very compatible with the Heck reaction, and the desired allylic alcohol products were obtained in yields of up to 92% and with excellent enantioselectivities of >99% ee in aU cases. This two-step one-pot process was, for example, successfully applied for the synthesis of (k)-(—)-rhododendrol ((J )-81) in 90% yield and with excellent (>99%) ee (Scheme 19.25) [65]. 

The palladium(II)-catalyzed reaction of haloarenes with alkenes and alkynes (Heck-type reactions) in aqueous media has become known only in the preceding few years [Eq. (14)]. 

Recent developments of Pd/Cu-catalyzed cross-coupling such as low-temperature coupling, use of long-lived paUadacycle catalysts, and coupling reactions in aqueous media were described. Although there have been tremendous developments in Pd-catalyzed systems for Heck-type reactions in the last decade, successful approaches toward the cross-coupUng reaction with terminal acetylenes are rare. 

Zhang Y, Yang J, Zhang X, Bian F, Yu W. A novel thermo and pH-double sensitive hydrogel immobilized Pd catalyst for Heck and Suzuki reactions in aqueous media. React Funct... 

Arenediazonium salts reacted with tetramethyltin under very mild conditions in acetonitrile yielding the corresponding toluenes [63] and this reaction could be carried out in aqueous media, as well [64] (Scheme 6.29). Similar to the Heck reactions discussed in 6.1.1, a one-pot procedure could be devised starting from anilines, with no need for the isolation of the intermediate diazonium salts. The pH of the solutions should always be kept below 7 in order to avoid side reactions of the diazonium salts, however, unlike with the Heck reactions, HCl or H2SO4 can also be used. Since organotin compounds are easily hydrolysed in acidic solutions, a careful choice of the actual pH is required to ensure fast and clean reactions. Diaryliodonium salts are hydrolytically stable and also react smoothly with various organotin compounds (Scheme 6.29) [65]. 

Heck-, Suzuki- and Stille-type Couplings - The Heck reaction, palladium-catalysed coupling of aryl or vinyl halides with alkenes or alkynes, is an extremely useful synthetic method. Only recently have Heck reactions been performed in aqueous media, probably due to the perception that water must be carefully... 

A polyethylene glycol-polystyrene graft copolymer palladium catalyst has been used in allylic substitution reactions of allyl acetates with various nucleophiles in aqueous media.58 Another polymer-bound palladium catalyst 40 was developed and used in a Heck coupling of allylic alcohols with hypervalent iodonium salts to afford the substituted allylic alcohols as the sole products under mild conditions with high catalytic efficiency.59 The same polymer-bound palladium catalyst has also been used for Suzuki cross-coupling reactions.60... 

A double Heck reaction of a reactant for which /3-hydride elimination is possible was described recently (117). The reaction was catalyzed by Pd(0) with phenanthroline ligand in aqueous media. 

Hiyama and co-workers have reported that the Mizoroki-Heck-type reaction of aryl- and alkenylsilanols is efficiently promoted by a Pd(OAc)2/Cu(OAc)2/LiOAc system (Equation (9)).50 50a in contrast, a dicationic Pd(ll) complex prepared in situ from Pd(dba)2, a diphosphine (dppe or dppben), and Cu(BF4)2 catalyzes 1,4-addition of aryltrialkoxysilanes to a-enones and a-enals in aqueous media (Equation (10)).51 The Pd-catalyzed 1,4-addition of the arylsilanes can be achieved also by using excess amounts of TBAF 3H20, SbCl3, and acetic acid.52... 

Iridium complexes as well as [Rh(OH)(cod)]2 can catalyze the Mizoroki-Heck-type reaction of arylsilanediols with acrylates. Aryltrialkoxysilanes activated by TBAF also work as the aryl donor in the presence of H20. In contrast to the Rh-catalyzed reaction, this reaction does not form / -arylated saturated esters even in aqueous media.69... 

Heck reactions are compatible with water (see Chapter 3.2.4) [35], which increases the speed of reaction in the presence of quaternary ammonium salts [36 a]. It is not surprising, then, that aqueous solvents (e. g. CH3CN/H2O) and water-soluble catalysts such as Pd(TPPTS)3 where TPPTS = P(C6H4-m-S03Na)3 [35, 67] can be employed successfully (eq. (10)). However, only aryl and vinyl iodides and aromatic diazonium salts (generated in situ from arylamines in aqueous media) are, up to the present, accessible to this method [36 b-h]. 

The reaction between aryl or alkenyl halides or arenediazonium salts and al-kenes catalyzed by palladium complexes, the so-called Heck reaction, has been performed in aqueous media. Arylation of styrene or acryHc acid derivatives occurred in high yields in the presence of a free-ligand palladium complex as catalyst and a base (Na2C03 or K2CO3) [96-98] and, eventually, a quaternary ammonium salt [Eq. (14)] [99,100]. 

The application of ethylene in Heck reactions often shows different activities from other alkenes, because of Wacker-type side reactions. It was found, however, that iodo- and acceptor-substituted bromoarenes are cleanly converted in aqueous media to the corresponding styrenes utilizing a palladium-TPPMS complex [13], Furthermore, high purity o- and p-vinyltoluenes were prepared on a large scale (in... 

SPHERICAL POLYELECTROLYTE BRUSH BASED METALLIC NANOPARTICLES 9 TABLE 1.2. Heck Reaction Promoted by Pd SPB in Aqueous Media"... 

In the last decade, a lot of attention has been paid to environmental aspects. As to the Mizoroki-Heck reaction, environmentally benign media currently involved in the design of catalytic systems encompass supercritical carbon dioxide (scCOa), fluorous systems, water and aqueous systems, solvent-free systems [66]. In this context, it should be noted that the so-called solvent-free reactions are actually not literally such, but are performed in media composed of substrates and often liquid amine. This was described as early as in 1972 by Heck himself [2, 8] (microwave heated version [53]). Amines are good coordinating solvents during the reaction, the amine is transformed into amine salt, which, being a major constituent or reaction mixture in the absence of a true solvent, adds to the net media polarity. 

Botella, L. and Najera, C. (2005) Mono- and jS,jS-double-Heck reactions of a, 8-unsaturated carbonyl compounds in aqueous media. J. Org. Chem., 70, 4360 9. 

Alacid, E. and Ndjera, C. (2006) PaUadated Kaiser oxime resin as precatalyst for the Heck reaction in organic and aqueous media. Synlett, 2959-64. 

Williams, D.B.G., Lombard, H. and Holzapfel, C.W. (2001) A comparative study of some Pd-catalysed Heck reactions in polar- and aqueous biphasic media. Synth. Commun., 31, 2077-81. 

Hayashi, M., Amano, K., Tsukada, K. and Lamberth, C. (1999) Efficient synthesis of unsaturated branched-chain sugars in aqueous media by Heck-type reaction. J. Chem. Soc., Perkin Trans. 7,239 0. 

As conclusion, the high catalytic efficiency of the polymeric palladacycle derived from Kaiser oxime resin similar to that of related unsupported dimeric pal-ladacycles was observed in the Mizoroki-Heck reaction. This polymer showed a good catalytic activity, not only in organic but also in aqueous media, for aryl iodides, bromides, and activated chlorides with high turnover numbers (TONs), rmder aerobic conditions at relatively lower temperature. 

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