Suzuki-Miyaura coupling generation

Iron-catalyzed Suzuki-Miyaura coupling reactions were also reported by Nakamura and colleagues (entry 27) [67]. Alkyl halides 1 and mixed pinacol aryl(butyl)borates, generated in situ from arylboronates and butyllithium, were used as the reagents and 10 mol% of the iron complexes 16a or 16b as the catalysts. The addition of 20 mol% of MgBr2 was essential for the success of the reaction. Products 3 were isolated in 65-99% yield. The methodology tolerates ester and nitrile functions. The reaction starts probably by initial boron-iron transmetalation to generate a diaryliron(II) complex. 

A year later, Schmidt and Rahimit ° reported ligand 77 (Figure 8) to be highly efficient in Suzuki-Miyaura coupling. Combining 77 with Pd(OAc)2, this in situ generated... 

Cyclopropyl arenes, alkynes and ALKENES from the IN srru GENERATION OF B CYCLOPROPYL 9 BBN AND THE SUZUKI-MIYAURA COUPLING OF ARYL, ALKYNYL AND ALKENYL BROMIDES... 

Chida et al. used this strategy for the total synthesis of murrastifoline A [204, 205]) and ( )-murrayazoline [( )-206] [206]. In addition to the double Buchwald-Hartwig amination generating the carbazole framework, two further palladium(0)-catalyzed couplings have been applied to construct the hexacyclic skeleton of ( )-murrayazoline [( )-206], an 0-arylation and a Suzuki-Miyaura coupling. Retrosynthetic analysis of ( )-murrayazoline [( )-206] led to 2-bromo-phenylboronic acid, the arylamine 211, and the monoprotected cyclohexane-1,4-dione 212 as precursors (Scheme 49). 

The highly reactive catalyst [PdPtBUa] can be generated by fast 1 1 micromixing of [Pd(OAc)2] and PtBUa and can be quickly transferred to the reaction vessel using a flow system to perform the Suzuki-Miyaura couplings [164]. 

Caztn and coworkers reported that easily prepared [(IPr)PdCl2] dimer 10 [14] and a series of mixed P(OR)3/NHC Pd complexes 11 [15] could be used in Suzuki-Miyaura coupling reactions at low catalyst loadings and at room temperature. For the latter, the authors carried out a series of experiments that suggested that alcohok or alkoxide groups play a major role in the activation of the complexes to generate the catalytically active Pd(0) species. 

Scheme 16.4 Selected results for Suzuki-Miyaura coupling with an in situ generated Pd-ADC catalyst.

The Suzuki-Miyaura coupling has traditionally been carried out using palladium as the metal catalyst however, there have been several reports that employ alternative metals as catalysts for the coupling reaction. In fact a rather controversial report even disclosed the use of no metal catalyst however, on careful examination of the reaction conditions it was found that palladium contaminants down to a level of 50 ppb found in commercially available sodium carbonate were responsible for the generation of the biaryl rather than an alternative non-palladium-mediated reaction. ... 

Suzuki-Miyaura coupling reaction. Despite the mechanism of this reaction not being very clear, the authors suggested that (see Scheme 3.8) the Pd(ll) catalyst reacts with the carboxylic acid to form the Pd(II)-carboxylate intermediate I, which subsequently decarboxylates to form the aryl-Pd(II) species II. After transmetallation of intermediate II with phenylboronic acid, intermediate III was generated. Reductive elimination afforded the desired product with regeneration of the Pd(0) catalyst. The Ag(l) salts were used to reoxidize the Pd(0) to Pd(II) catalyst, thus completing the catalytic cycle (see Scheme 3.8) [20]. 

A dichromium derivative has been prepared from pinacol (dichloromethyl)-boronate (163), anhydrous chromous chloride, and lithium iodide in THF at 25 °C [90]. With various aldehydes, RCHO, this reagent adds to the carbonyl carbon to form trans-l-alkenylboronic esters, RCH=CH-B(02C2Me4). For most examples yields were 84-91%, E Z ratios >95 5. This reaction was used recently to convert aldehyde 162 into alkenylboronic ester 164, an intermediate used for a Suzuki-Miyaura coupling in the asymmetric total synthesis of quinine and quinidine (Scheme 8.39) [91]. In the modified procedure, the chromium reagent was generated from 163 in the presence of the aldehyde substrate. 

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