Stille-type cross-coupling

The traditional Stille-type cross coupling of stannane 88 with bromopyrimidine 89 was reported by Fort and co-workers to provide pyrimidine 90 in 80% yield <00OL803>. This illustrates a novel route to heterocyclic chlorobiaryls. 

In the presence of in, V -generated palladium(O) species, an electrophilic 7t-allyl complex 228 is formed, which is readily engaged in an intramolecular carbometallation (Scheme 57). The resulting vinylpalladium species then undergoes a Stille-type cross-coupling to provide a triene.232... 

In principle, three basically different types of reaction modes are applied for cross-coupling reactions of allenes. First, cross-couplings of allenes with suitable halogen or metal substituents at one of the sp2-hybridized carbons furnish products still bearing the intact cumulene it-system. On this basis, numerous reactions for conversions of precursor 1 or 3 into substituted allenes 2 have been developed (Schemes 14.1 and 14.2). 

Hartwig-Buchwald, Suzuki, and Stille type cross-coupling reactions with key intermediate 46 led to a wide range of substituted sulfoximines such as 47-49 [37]. In order to demonstrate the synthetic utility of the resulting products, pseudo tripeptide 50 was prepared from a related intermediate. 

The same authors also presented a completely selective three-component cascade reaction but of a slightly different type. By reacting 26 with a vinyl-stannane 27 (R = SnBus) in the presence of methyl acrylate or diethyl maleate, a sequential Stille-type [31] cross-coupling-Diels-Alder reaction took place, which only gave the desired products [30]. Since the Stille coupling proceeds without a base present, the dienophile does not participate in a Heck reaction, but only in a [4 + 2] cycloaddition with the initially formed electron-rich diene. 

Palladium-catalyzed Stille cross-coupling of furanylstannanes to an allyl bromide was also regioselective. An example, as employed in the total synthesis of 6/3-hydroxyeuryopsin, is depicted in Equation (38) <2004CC44>. This type of reaction could also be performed by using a catalytic amount of CuCl, rather than a palladium catalyst <1999SL1942>. 

Thus, an efficient and convergent total synthesis of ( )-isocembrene has been accomplished in seven steps from the known geranylacetone through an intramolecular Stille cross-coupling reaction. The strategy is of great potential for the divergent synthesis of complex cembrane-type diterpenoids such as cembrene-C and sarcophytols. 

Stille and Suzuki cross-coupling reactions failed when the authors tried to obtain the mono-arylated pyrrole under different conditions. As a consequence, these types of coupling reactions would not seem to be useful in providing access to differentially di-arylated pyrrole systems... 

Reaction of 6-iodo-9-(2,3,5-tri-0-acetyl-/3-D-ribofurano.syl)purine with tetramethyltin in the presence of tetrakis(triphenylphosphane)palladium(0) gives, after deprolection, 6-methyl-9-(/(-D-ribofurano.syl)purine 22 (Stille cross coupling). This is the most straightforward synthesis for this type of compound described in the literature. 

Pd-catalyzed C-C-coupling reactions of the Heck type, e. g., Suzuki [48c] and Stille [49c] cross-coupling, are excellent tools for the preparation of biaryls (see also Section 3.1.9). The activity and stability of the catalyst is highly dependent on the steric and electronic properties of the ligands. Sterically demanding basic alkylphosphines e. g., tri(/-butyl)phosphine, have proven to be very effective ligands in the Heck reaction [50] as well as in the Suzuki cross-coupling [51]. NHCs resemble those basic phosphines (see above) and therefore were tested... 

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