Palladium acetate phase-transfer catalyst

Vinyl iodides are considerably more reactive than bromides in the vinylations. It may be presumed that chlorides are not generally useful, with one exception noted below, since they have not been employed in the reaction. The bromides are usually reacted with a palladium acetate-triphenyl- or tri-o-tolyl-phos-phine catalyst at about 100 C. The reaction will occur without the phosphine if a secondary amine is present. Vinyl iodides will react in the absence of a phosphine even with only a tertiary amine present.48 37 The iodides are so reactive, in fact, that reactions occur even at room temperature if potassium carbonate is the base and tetra-zi-butylammonium chloride is used as phase transfer agent in DMF solution when palladium acetate is the catalyst.88... 

While alkyl halides are typically employed as an electrophile for this transformation, Takemoto developed palladium-catalyzed asymmetric allylic alkylation of 1 using allylic acetates and chiral phase-transfer catalyst 4k, as depicted in Scheme 2.5 [ 2 3 ]. The choice of triphenyl phosphite [(PhO)3P] as an achiral palladium ligand was crucial to achieve high enantioselectivity. 

Takemoto and coworkers extended their palladium-catalyzed asymmetric allylic alkylation strategy using allyl acetate and chiral phase-transfer catalyst to the quaternization of 13 [23b]. A correct choice of the achiral palladium ligand, (PhO P, was again crucial to achieve high enantioselectivity and hence, without chiral phosphine ligand on palladium, the desired allylation product 15 was obtained with 83% ee after hydrolysis of the imine moiety with aqueous citric acid and subsequent benzoylation (Scheme 2.12). 

CONJUGATE ADDITION (3-Bromopropion-aldehyde ethylene acetal. 1-r-Butylthio-1 -trimethylsilyloxyethylene. Cryptates. l-EthylsuIfinyl-3-pentanone. HexamethyF phosphoric triamide. Ketene bis-(methylthio)ketal monoxide. Organo-lithiuni compounds. Palladium(II) chloride. Phase-transfer catalysts. 

The palladium-catalyzed arylation of alkenes and arenes offers one of the conceptually most intelligent solutions for the synthesis of PAHs from the appropriate aryl halides or triflates. The reaction is usually carried out in a polar solvent (AT,AT-dimethylformamide (DMF) or AT,AT-dimethylacetamide (DMA)) at relatively high temperatures (100-170°C) with a base to trap the acid formed, and a phase transfer catalyst. Most often Pd(II) acetate or a Pd(II) complex are used, that are converted to a catalytically active Pd(0) species in the course of the reaction. The mechanisms of these Heck reactions have been discussed widely throughout the pertinent literature [78,79]. 

Palladium (II) acetate, tetrabutyl ammonium bromide (a phase-transfer catalyst) and potassium carbonate in a mixture of acetonitrile and water, which were originally published by Jeffery in 1996 for Heck reactions, have also been applied to C-H activation of thiophenes. Lemaire and coworkers have coupled a number of 2- and 3-substituted thiophenes (-CHO, -NO2, -CN) with iodobenzenes, albeit in low yields (Scheme 19.2). 

Formation of Allyl and Aryl Primary AUyUc and HomoallyUc Alcohols from Vinyl Epoxides and Oxetanes. Vinylic epoxides can be coupled with aryl (eq 30) or vinyl (eq 31) iodides or tri-flates to form allylic alcohols in 40-90% yield. When employing palladium acetate as the catalyst, a reducing agent such as sodium formate is required in addition to the salts normally present under phase transfer conditions. 

Tetrakis(triphenylphosphane)palladium(0) is the catalyst of choice, but palladium ) acetate and other Pd(II) and Pd(0) sources have also been used. The intensively studied catalytic cycle requires two equivalents of base and the reaction is often carried out under phase transfer conditions. However, newly developed palladacycles from palladium(II) acetate and selected triarylphosphanes show much higher turnover numbers, do not decompose significantly at the... 

Leadbeater et al. recently showed that the PTC procedure with MW irradiation can be used to prepare of biaryls using water, palladium acetate, and TBAB as solvent, catalyst, and phase-transfer agent, respectively [117]. The desired coupling products were obtained in good yield (60 to 90%). The reaction can, however, be performed equally well using MW and conventional heating methods. Although it... 

Hydrogenation of hulupone and cohulupone in the presence of platinum(IV) oxide or palladium(il) chloride as catalysts affords in both cases a hexahydroderivative and an octahydroderivative (2,16,22). With palladium on barium sulfate only a hexahydrohulupone or a hexahydrocohulupone is formed (87%). Thus hexahydrocohulupone gives 2-(3-methylbutanoyl)-5,5-bis(3-methylbutyl)-3,4-di-hydroxy-2-cyclopentenone (211, Fig. 88), which also may be considered as 5-(3-methylbutyl)dihydrocohumulinic acid. Cohulupone leads to 5,5-bis(3-methylbutyl)-3,4-dihydroxy-2-(2-methylpropanoyl)-2-cyclopentenone or 5-(3-methylbutyl)dihydro-cohumulinic acid (210, Fig. 87). This compound is identical to that obtained by sequential oxidation, reduction and alkaline treatment of hexahydrocolupulone (see 13.1.1.2.2.). Compound 210 (melting point 48°C) is isolated from the band with distribution coefficient 0.475 after 450 transfers in the two-phase system iso-octane acetate buffer in methanol water 58 42 with pH 5.45 (8). The molecular formula is C19H32O4 and the pK/ value in methanol water 1 1 is 4.1. In the H NMR spectrum... 

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