Suzuki cross-coupling boronic acids

Vinylation can also be done by Pd-catalysed cross-coupling in which one component is used as a halide or triflate and the other as a stannane (Stille reaction) or boronic acid (Suzuki reaction). Entry 9, Table 11.3, is an example of the use of a vinylstannane with a haloindole. lndole-3-boronic acids, which can be prepared by mcrcuration/boration, undergo coupling with vinyl triflates (Entry 10). 

FuNn iONAL Group Tolerance of PdildbrO VIMes.HCI Catalyzed Suzuki Cross-Coupling Reactions of Aryl Chlorides with Phenyi.boronic Acid Derivatives... 

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo- and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [174]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [175]. A solventless Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as a base [176], This approach has been extended to Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 6.52) [177]. 

In this method, Furstner converts N-BOC protected pyrrole to the 2,5-dibromo compound (122) with NBS and this is followed by metalation and carbomethoxylation with t-butyl lithium in THF and subsequent trapping of the metalated species with methyl chloroformate to yield a pyrrole diester (123). Bromination of this diester at positions 3 and 4 with bromine in water followed by Suzuki cross-coupling with 3,4,5-trimethoxyphenyl boronic acid yields the symmetrical tetrasubstituted pyrrole (125). Base-mediated N-alkylation of this pyrrole with 4-methoxyphenethyl bromide produces the key Boger diester (126) and thereby constitutes a relay synthesis of permethyl storniamide A (120). 

Vilsmeier reaction of 2-oxindole (830) afforded 2-chloroindole-3-carbaldehyde (891). Suzuki cross-coupling of 891 with furan-3-boronic acid (1124), followed by protection of the indole nitrogen with benzyloxymethyl (BOM) chloride, led to... 

Chemists working to develop new bioactive compounds try to be alert for new stable heterocycle platforms, but they can easily overlook some of the more, shall we say, exotic ones. When one thinks about the utility of boron in heterocyclic chemistry, the Suzuki cross-coupling reaction typically first comes to mind. In this valuable synthetic reaction <95CRV2457>, a boronic acid group is discarded under basic conditions during a Pd-catalyzed C-C bond formation. There are exceptions, of course, but few chemists appreciate that boron is an element that can be valuable to retain in a molecule so that its unique properties can be utilized. 

In a simple strategy to biaryl formation, Han et al.89 showed that silicon-directed ipso-substitution and concomitant cleavage from supports could be used for formation of functionalized biphenyls. For this they used a tethered silyl aryl bromide in a Suzuki cross-coupling reaction, followed by the ipso-substitution/cleavage step (Scheme 39). A variety of boronic acids were coupled in this manner. The only difficulty occurred with electron-deficient nitrophenylboronic acid where the desired product was formed under anhydrous conditions in only 33% yield (the remainder being starting material). Reversion to the more usual conditions of aqueous base-DME (i.e., those used by Frenette and Friesen)70 improved the yield to 82%. 

In 2001, Cammidge et al. [47] reported the preparation of an MIP for Suzuki cross-coupling between p-bromoanisole (68) and phenyl-boronic acid (69) to give the corresponding 4-methoxy-biphenyl (70). 

Schliiter et al. successfully accomplished generation-specific incorporation of an individual aryl bromide functionality into poly(benzyl ether) dendrimers. Whatever its position in the dendrimer framework, this bromide function could also be utilised for further chemical modification because it can react with aryl-boronic acid via Suzuki cross-coupling [42]. 

Thus, for our present purposes a similar approach was followed using Suzuki cross-coupling reactions as the key steps in the synthesis of our target compounds. Symmetrically substituted compounds were synthesized in a twofold Suzuki crosscoupling reaction from commercially available p-substituted phenylboronic acids or esters and 4,4 -dibromobiphenyl or 4,4 -biphenyl-bis-boronic acid ester and a p-substituted arylhalide, respectively, using tetrakis (triphenylphosphino) palladium as catalyst together with cesium fluoride as base in dry tetrahydrofurane as shown in Scheme 8.1. The desired products were obtained in respectable yields after heating at reflux for 50 h. 

Assuming that the general methodology in Scheme 62 would be applicable, catechol precursors were required for the C-4 pyridone substituents of 5 and 6. This led (using analogies to the catechol cleavages illustrated in Schemes 4 and 5) to a requirement for boronic acids 178 and 179 for use in the Suzuki cross-coupling step (Scheme 64). 

Boronic Acid Preparation/Suzuki Cross-Coupling... 

Recently, we used hyperbranched polyglycerol 1 as a high-loading support for boronic acids with application in the palladium-catalyzed Suzuki cross-coupling reaction [79]. Moreover, hyperbranched polyglycerol (1) can... 

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