Pd 2, dppf

Fig. 30 Microwave-promoted fluorous synthesis of biaryl-subshtuted proline analogs. Reagents and condihons a EtaN, DMF, MW 150 °C, 15 min, 40-75%, closed vials b R""PhB(OH)2, Pd(dppf)Cl2, K3PO4, toluene Acetone H2O, MW 120 °C, 12 min, sealed vial system, 19-79%. R=Me, Et R = Me, 1 - Pr R" = H, 3-MeO R" =Me, Et R""= 4-MeO, 3-Cl, 4-Ac,3,4-diCl,3,4-methylenedioxy...

Fig. 41 Representative example of microwave-assisted Suzuki couplings in fluorous phase. Reagents and conditions [Pd(dppf)Cl2], K2CO3, toluene/acetone/H20, MW 130°C, 10 min, closed system, 78%...

An interesting parallel was found while the microwave-enhanced Heck reaction was explored on the C-3 position of the pyrazinone system [29]. The additional problem here was caused by the capability of the alkene to undergo Diels-Alder reaction with the 2-azadiene system of the pyrazinone. An interesting competition between the Heck reaction and the Diels-Alder reaction has been noticed, while the outcome solely depended on the substrates and the catalyst system. Microwave irradiation of a mixture of pyrazinone (Re = H), ethyl acrylate (Y = COOEt) and Pd(dppf)Cl2 resulted in the formation of a mixture of the starting material together with the cycloaddition product in a 3 1 ratio (Scheme 15). On the contrary, when Pd(OAc)2 was used in combination with the bulky phosphine ligand 2-(di-t-butylphosphino)biphenyl [41-44], the Heck reaction product was obtained as the sole product. When a mixture of the pyrazinone (Re = Ar) with ethyl acrylate or styrene and Pd(dppf)Cl2 was irradiated at 150 °C for 15 min, both catalytic systems favored the Heck reaction product with no trace of Diels-Alder adduct. 

Thus, reaction of 6/1-229 with the diborane 6/1-230 in the presence of catalytic amounts of Pd(dppf)2Cl2 in high dilution afforded 6/1-231 in 45% yield (Scheme 6/1.59). 

The reaction of benzotriazoles with aryl halides catalyzed by a mixture of Pd(dppe)Cl2 (DPPE = bis-(diphenylphosphino)ethane) or Pd(dppf)Cl2, copper(I)iodide or copper(II)carboxylates, and a phase-transfer catalyst has been shown to proceed in good yield in DMF solvent.104 Both copper and palladium were required for these reactions to occur at the N-l position in high yields. Similar results for the coupling of amines with aryliodonium salts in aqueous solvent were observed.105... 

Pd(dppf)Cl2] was used as the catalyst. A particularly noteworthy aspect of this publication is the introduction of a one-pot borylation/Suzuki reaction of 5-bromo-terthiophene with commercially available bis(pinacolato)diboron. The resulting sex-ithiophene was obtained within 10 min of microwave irradiation in 84% isolated yield. The same concept was also applied for the synthesis of modified oligothio-... 

In a related approach from the same laboratory, the perfluorooctylsulfonyl tag was employed in a traceless strategy for the deoxygenation of phenols (Scheme 7.82) [94], These reactions were carried out in a toluene/acetone/water (4 4 1) solvent mixture, utilizing 5 equivalents of formic acid and potassium carbonate/[l,T-bis(diphe-nylphosphino)ferrocene]dichloropalladium(II) [Pd(dppf)Cl2] as the catalytic system. After 20 min of irradiation, the reaction mixture was subjected to fluorous solid-phase extraction (F-S PE) to afford the desired products in high yields. This new traceless fluorous tag has also been employed in the synthesis of pyrimidines and hydantoins. 

For the Suzuki coupling of 5-bromopyrimidine and protected p-boronophenylalanine 52 to assemble 53, Pd(dppf)Cl2 was found to be an effective catalyst [28], whereas using 2-bromopyrimidine as the substrate gave the corresponding adduct in only 20% yield. 

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