Palladium catalysis aryl bromides

The ring closure to form butenolides by palladium(O) catalysis can be combined with C,C bond linking, as shown by Ma and co-workers. If using tetrakis (triphenyl -phosphane)palladium(O), the products 272 are obtained from 268 (R1 = alkyl, R2 = H) and vinyl iodides or aryl bromides and iodides R3X [304]. The authors assume that... 

Ellman used silyl chemistry for the direct linkage of aromatics onto the solid support by converting an aryl bromide to aryl lithium and reacting this with a silyl resin.90 It is the production of the silyl resin that is of interest in the context of this review, since an in situ Suzuki coupling was used to link the allyl silane to bromomethyl polystyrene resin (Scheme 40). 9-BBN is used to carry out the regioselective hydroboration, and this is linked to the resin with palladium catalysis in the usual way. After brief exposure of this... 

In the last few years numerous reports have been published in the field of microwave-promoted aryl halide cyanation, utilizing nickel [71], palladium [72,73] and copper [74,75] catalysis. Even water [75] and ionic liquids [76] have proven useful as solvents in these processes. Srivastava and Collibee have exemplified a swift and dynamic procedure using polymer-supported triphenyl phosphine to enable easy subsequent removal through filtration [72]. As shown in Scheme 19, both bromides and iodides could be activated using palladium catalysis in DMF. Even without optimization of the individual reaction times, the overall process time involving simple filtration and extraction for compound isolation appears to be short. 

Clarke recently published the first microwave-accelerated Hiyama coupling [163,164]. It was noted that the availability and nontoxic attributes of the organosilicon reactants make them very attractive in synthesis, but their low nucleophilicity limits their potential. Microwave heating allowed aryl bromides and activated aryl chlorides to react under palladium catalysis using an electron-rich N-methyl piperazine/cyclohexyl phosphine ligand (Scheme 75). A vinylation reaction with vinyltrimethoxysilane was also reported [164],... 

Other unsaturated substrates arylated by various diaryl iodonium salts included butenone, acrylic acid, methyl acrylate and acrylonitrile [46]. Allyl alcohols with diaryliodonium bromides and palladium catalysis were arylated with concomitant oxidation for example, from oc-methylallyl alcohol, aldehydes of the general formula ArCH2CH(Me)CHO were formed [47]. Copper acetylide [48] and phenyl-acetylene [49] were also arylated, with palladium catalysis. 

Utilisation of transition metal benzothiazol-2-yMene and especially thiazol-2-ylidene complexes in homogenous catalysis reactions are very rare [42-44], Calo et al. reported the use of bis-(3-methyl-benzothiazol-2-ylidene) palladium diiodide in the Heck reaction of aryl bromides and iodides with a catalyst loading of down to KU mol% and near quantitative yields [42,44],... 

Further improvements in palladium catalysis were achieved with a larger excess of benzene as co-solvent, and also with DavePhos (95) as ligand and pivalic acid as additive (Scheme 9.31) [70]. This catalytic system tolerated various valuable functional groups, such as a nitro substituent. These reaction conditions allowed not only for the achievement of better yields of biaryls with aryl bromides as electrophiles, but also improved chemoselectivies of these transformations. Thus, in competition experiments between benzene (87) and fluorobenzene (96), the latter reacted preferentially in a ratio of >11 < 1 (Scheme 9.31) [70],... 

A -Arylation of pyrroles can be achieved by conversion of 1-lithiopyrroles into the corresponding zinc compounds and then reaction with aryl bromides using palladium(O) catalysis or by direct reaction of the pyrrole with an aryl halide in the presence of base and the palladium catalyst. ... 

Aryl iodides are more reactive towards oxidative addition than aryl bromides, and a selective Heck coupling (without phosphine ligands) with an unsaturated side chain left the bromide in place. A second Heck reaction of this bromide with an allylic alcohol was used to introduce a second side chain. Cyclization of the amide on to the allylic alcohol was achieved with palladium catalysis, not as might have been expected with palladium(O) but instead with palladium(ll), to produce the seven-membered ring. Finally, the conjugated double bond was reduced and the sulfonamide removed under photolytic conditions. 

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