Stille and Suzuki couplings

Interestingly, Hiyama couplings, similar to Stille and Suzuki couplings but involving silanes instead of stannanes or borates, required stoichiometric amounts of silver salts.74 However, the silanes must be activated to obtain effective transformations, and usually, vinyl- or arylsilanols are used in such couplings. Among the silver salts, the oxide proved again to be the most active promoter (Scheme 10.43).75... 

The coupling of terminal alkynes with aryl or vinyl halides under palladium catalysis is known as the Sonogashira reaction. This catalytic process requires the use of a palladium(0) complex, is performed in the presence of base, and generally uses copper iodide as a co-catalyst. One partner, the aryl or vinyl halide, is the same as in the Stille and Suzuki couplings but the other has hydrogen instead of tin or boron as the metal to be exchanged for palladium. 

Keywords Oxazolines Direct Stille and Suzuki coupling Diisopropylcarbo-diimide cyclization Chemotherapeutic agent Anti-HIV activity... 

The Heck reaclion differs from Stille and Suzuki coupling in that no stoichiometric metallic coupling partner is used. Also, a i-hydride elimination rather than a reductive elimination of Iwo groups generates the product. 

Many compounds containing metal-metal bonds undergo Stille and Suzuki couplings, too. Two of the most popular reagents for this purpose are hexam-ethyldistannane (Me3Sn-SnMe3) and pinacoldiborane [(pin)B-B(pin), where pin = l,l,2,2-tetramethylethylene-l,2-dioxy]. In fact, even (pin)BH itself will convert aryl halides to arylboronates when an amine is present to neutralize the HX by-product. In this case, the mechanism by which the B-H bond is converted to a B-Pd bond is somewhat murky. 

Synthesis of pyrazine alkaloid, botryllazine A, involved a combination of the Stille and Suzuki coupling reactions. The Suzuki coupling of 6-substituted 2-chloropyrazine 69 with 4-methoxyboronic acid produced 2,6-diarylpyrazine 70 [29]. 

Intramolecular coupling of 120 having an aryl iodide group and a vinylstannane group accomplished the total synthesis of (-)-zealarenone (99) (Scheme 19) [77]. The first total synthesis of macrolactin A (124) was efficiently accomplished based on the Stille reaction of 122 for both stereospecific construction of the diene moieties and closure of the 24-membered macrocyclic ring [78]. The key precursor 122 was synthesized via two Stille couplings and Mitsunobu esterification. An alternative route to the dimethyl ether 125 was reported by cyclization of 123, which was prepared by the Stille and Suzuki couplings followed by DCC-DMAP esterification... 

The process involving aryltrialkoxysilanes is an alternative to Stille and Suzuki couplings. Change of reaction conditions permits the synthesis of either styrenes or P-silylstyrenes from vinyltrimethylsilane. ... 

These versatile reactions, commonly referred to as Stille and Suzuki couplings, respectively, are performed with organostannanes or organoboranes as nucleophiles and are tolerant to most functional groups. Ketones are obtained if carbon monoxide is present in the Stille reaction. This gives the possibility to label an aromatic methyl ketone in two different positions by the use of either [ C] carbon monoxide or [ C] methyl iodide, as shown in O Fig. 41.22 (Andersson et al. 1995 Andersson and Langstrom 1995a, b). 

A second common class of catalytic reaction is coupling (eq. 24), where A-B is the desired product and the nature of X and Y can be chosen to give the reaction the necessary exothermicity to go forward and facilitate the interaction of the reagents with the catalyst. In this class, we have Stille and Suzuki coupling, as well as more recent versions involving carbon-heteroatom bond formation... 

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