SUZUKI COUPLING ACCELERATED

To date a number of reactions have been carried out in ionic liquids [for examples, see Dell Anna et al. J Chem Soc, Chem Commun 434 2002 Nara, Harjani and Salunkhe Tetrahedron Lett 43 1127 2002 Semeril et al. J Chem Soc Chem Commun 146 2002 Buijsman, van Vuuren and Sterrenburg Org Lett 3 3785 2007]. These include Diels-Alder reactions, transition-metal mediated catalysis, e.g. Heck and Suzuki coupling reactions, and olefin metathesis reactions. An example of ionic liquid acceleration of reactions carried out on solid phase is given by Revell and Ganesan [Org Lett 4 3071 2002]. 

ACCELERATED SUZUKI COUPLING VIA A LIGANDLESS PALLADIUM CATALYST 4-METHOXY-2 -METHYLBI PHENYL (1,1 -Biphenyl, 4 -methoxy-2-methyl-)... 

ACCELERATED SUZUKI COUPLING VIA A LIGANDLESS PALLADIUM CATALYST 4-METHOXY-2 -METHYLBIPHENYL... 

Similar to the case of Suzuki couplings (6.1.2), ally lie alkylations can also be run in neat water as solvent in the presence of surfactants. In addition to the general solubihzation effect, the amphiphiles may also have a specific influence on the reaction rate. For example, the reaction of the P-ketoester substrate on Scheme 6.22 with allyl acetate, catalyzed by [Pd(PPh3)4] was only slightly accelerated by the anionic SDS (1.5 h, 18 % yield), however, the reaction rate dramatically increased in the presence of the cationic CTAB and the neutral Triton X-100 detergents, leading to 74 % and 92% yields in 1.5 h and 5 min ( ), respectively [51]. Several other carbonucleophiles were alkylated in such emulsions with excellent yields. 

The (Z, , )-triene systems in leukotriene and DiHETE were constructed by the coupling of the (ZfT)-dienylborane with the (Z)-alkenyl iodide [129,130]. In the total synthesis of the naturally occurring large molecule palytoxin, which has numerous labile functional groups, Suzuki coupling gives the best results for the creation of the (E,Z)-, 3-diene part (290) by the coupling of the alkenylborane 288 with the (Z)-alkenyl iodide 289. In this case, thallium hydroxide as the base accelerates the reaction 1000 times more than KOH [131]. 

The mechanism is very similar to that of the Stille coupling. Oxidative addition of the vinylic or aromatic halide to the palladium(O) complex generates a palladium(II) intermediate. This then undergoes a transmetallation with the alkenyl boronate, from which the product is expelled by reductive elimination, regenerating the palladium(O) catalyst. The important difference is the transmetallation step, which explains the need for an additional base, usually sodium or potassium ethoxide or hydroxide, in the Suzuki coupling. The base accelerates the transmetallation step leading to the borate directly presumably via a more nucleophilic ate complex,... 

Accelerated Suzuki Coupling via a Ligandless Palladium Catalyst 4-Methoxy-2 -methylbiphenyl. 

These early results led us to investigate the feasibility of carrying out Suzuki coupling reactions on alumina in the absence of solvents. We investigated both thermal and microwave-assisted reactions, eq 4, Microwave irradiation of organic reactions has gained in popularity in recent years since it was found to accelerate a wide variety of transformations (26,27)... 

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