Selectivity cross-coupling

Highly selective cross-coupling benzoin condensations have been achieved via the use of enzymatic methods. ... 

The 121/Cl3SiH combination selectively cross-couples alkenes with alkynes intermolecularly to give acyclic homoallylic silanes 127 and 128 (Eq. 22) [73]. 

Olefin metathesis enables the catalytic formation of C=C double bonds under mild conditions.1 After the development of well-defined catalysts,1 2 selective cross-couplings between functionalized terminal alkenes (CM) have been noted.2 A general problem... 

It is also possible to perform copper-catalyzed alkylation of arylmagnesium compounds. Thus, the copper reagent 48 undergoes a selective cross-coupling [28] with ethyl 4-iodobutyrate to furnish the desired product 49 in 69% yield (Scheme 2.12) [29]. 

Dibutylbenzene has been prepared from cyclohexanone by tedious, multistep procedures.3 4 The present one-step method is based on the selective cross-coupling of a Grignard reagent with an organic halide in the presence of a phosphine-nickel catalyst.3... 

Such recombinations produce self-coupled dimers. In general, selective cross-coupling of two radicals (A- + B- - A—B) cannot be conducted because (i) the two radicals are generated at the same rate and... 

Scheme 29. Selective cross-coupling of 2-naphthol (68a) and 2-naphthylamine (70a) mediated bycopper(ll) and an amine base.

In the presence of a base (Et3N) the ruthenium vinylidene complex RuCl(Cp )(PPh3)(=C=CHPh) promotes the selective cross-coupling of a bulky terminal alkyne with internal alkynes at room temperature to yield functionalized enynes (Eq. 10) [77]. 

Z-selective cross-coupling of terminal alkynes with isocyanides to exclusively yield (Z)-l-aza-l,3-enyne products has been achieved for the first time using a constrained geometry catalysts [Y(C5Me4Si(Me2)NR)(Alk) (THF)X] (Aik = R, dimethylaminobenzyl R = lBu, Ph, 2,4,6-Me3C6H2. The intermediate was shown to be the acetylide-bridged dimer [Y(C5Me4Si (Me2)NR)(p-C=CPh)]2.41 [24]... 

If the alkyne in the second step is a 1-aryl propargyl alcohol the product is a bischalcone as a consequence of a CIR-CIR sequence. Furthermore, it is also possible to perform CIR-Heck and CIR-Suzuki sequences if alkenes or boronates and potassium carbonate are added after completion of the initial CIR step. Here again, the gradual differences in reactivity in the oxidative addition between an electron-deficient and an electro-neutral carbon-bromine bond can be readily exploited for selective cross-coupling, first to furnish an aryl propargyl alcohol that is slowly isomerized upon base catalysis to give the bromo chalcone for further cross-coupling. 

Both BAL and BFD can be applied for R-selective cross coupling reactions between two aromatic aldehydes (Scheme 5.12). This opens a direct access to a huge variety of compounds. Their stereoselectivity in these reactions is identical, their substrate specificity however, is not. Of particular interest is that BFD is only R-selective for the coupling of two aromatic aldehydes. For the coupling of... 

The low oxidation potentials of stannyl compounds gave us a clue to develop the selective cross-coupling reaction between the a-posi-tions of two carbonyl compounds. Generally, silyl enol ethers or ketene silyl acetals are employed for this purpose to prepare 1,4-di-... 

Selective cross-coupling reactions between C(sp ) and C(5p ) centers had been one of the most difficult tasks in carbon-carbon bond synthesis until the early 1970s, when it was first reported that iron, nickel, palladium and copper - catalysts are extremely effective for cross-coupling of Grignard reagents with organic halides. Now, nearly 20 years later, transition metal catalyz cross-coupling has become the reaction of first choice for this purpose. 

Shikonin. Torii has accomplished an efficient intermolecular pinacol coupling reaction, en route to the total synthesis of shikonin, a compound with antiinflammatory, antibacterial, and antitumor activity (Eq. 3.11) [29], Because the aromatic aldehyde possessed a substituent capable of chelating to vanadium, Torii anticipated, based on precedent, that selective cross-coupling would be possible. The pinacol reaction proceeded in 73% yield and with good diastereoselectivity (5.5 1). 

Selective cross-coupling of secondary organozinc reagents... 

Basu et al. have reported palladium-catalyzed selective cross coupling of bromo-pyridines and amines on the surface of potassium fluoride supported basic aluminium oxide [5]. For example, amination of 2,6-dibromopyridine by this method afforded the monoaminated products predominantly, even after prolonged the reaction time and using excess amine, whereas previous method [6] gave only bis-aminated products (Scheme 5.3). 

Scheme 5.3 Palladium-catalyzed selective cross coupling of bromopyridines and amines on potassium fluoride supported basic aluminium oxide.

Phosphine-nickel and -palladium complexes have been used as catalysts for the reaction of Grignard reagents (RMgX) with vinyl or aryl halides (R X ) to produce, selectively, cross-coupling products (R-R ). The catalytic cycle of the reaction has been proposed to consist of a sequence of steps involving a diorgano-metal complex (LnM(R)R ) as a key intermediate (Scheme I). 

Molybdenum imido alkylidene complexes also have been employed for a variety of other catalytic reactions of interest to the organic or polymer chemist, among them selective cross-couplings of olefins, [99] polymerization of terminal alkynes, [100-102] step-growth polymerization of dienes, [103,104] and cyclopolymerization of 1,6-heptadiynes. [105-107]... 

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