Stille couphng

On the other hand, the stereoselective synthesis of the masked half of the disorazole Al involved the Stille couphng of oxazole-dibromoolefine 62 with diene 63 and the expected key intermediate, bromotriene 64, was assembled in excellent yield [15],... 

Some Stille couphngs have been accelerated by Cu co-catalysis. The role of the copper herein is to scavenge 16-electron tin species [191] formed after dissociation of strong ligands such as phosphines [192], Mechanishc studies by Casado et al. 

Palladium black precipitates on the resin during Stille coupHng. After removal of the reaction solution and rinsing of the resin, a brief treatment with dilute KCN in DMSO clears the precipitate from the resin. 

A similar method has been used for boronic acid couplings of 3-methylthio-l,2,4-triazine, using Cu(I) 3-methylsaUcylate as the additive and for Stille couphngs of a wider range of heterocyclic substrates." ... 

Pattenden and co-workers reported the total synthesis of 14,15-anhydro-pristinamycin 11b 1219. Retrosynthetically, the authors proposed a late-stage construction of the macrocyle via an sp -sp Stille couphng of the vinyl stannane 1220... 

Prakash and Thompson used monodisperse poly(4- and poly(2-vinylpyridine) nanospheres as stabilisers to support 1-4 nm Pd nanoparticles in a study concerning the Heck, Suzuki and Stille couphng reactions [14]. The material was found to be very active. However, the reactions were Umited to the couphng of the highly reactive 4-bromo-nitrobenzene with, respectively, butyl acrylate, phenylboronic acid and phenyl-trimethylstannane. No noticeable influence of the nature of the stabilisers was reported in this study. The authors argue that the material was stable under the reaction conditions, but this conclusion is only based on macroscopic TEM analyses. In view of the low Pd concentration which was required to perform effective Heck, Suzuki or Stille coupling reactions, it is not surprising that no major variation of the Pd particle size was observed. 

Scheme 1.8). The Stille coupHng of alkenylstannanes with alkyl bromides that possess P-hydrogens is possible at room temperature, with [Pd(P(tBu)2Me)2] as the catalyst [133]. In this case, the addition of fluoride was required to enhance the reactivity of the stannane. 

Verkade etal. usedproazaphosphatranes (Scheme 6.13) for the Stille coupHngs of aryl chlorides under mild reaction conditions. These unusually electron-rich Hgands are also suitable for reactions of sterically congested substrates, and crossaryl bromides can be achieved at room temperature [31b,c]. 

Reactions Catalytic in Tin Maleczka and Terstiege [72] have published several papers in this area. They first developed a one-pot hydrostannylation/Stille couphng protocol for reactions between 1-alkynes and bromostyrene to give 1,3-dienes. A mixture of BUjSnCl (catalytic amount), polymethylhydrosiloxane (PMHS) and aqueous sodium carbonate (to convert the chloride to bis(tri-n-butyltin)oxide that reacts with PMHS to give BUjSnH in situ) in combination with Pd2(dba)j and trifurylphosphine leads to diene formation. Use of MejSnCl instead of the tributyltin chloride [73] improves yields drastically (to up to 90%). Further improvement is obtained in the third protocol reported [74a,b], which was used to prepare... 

Not many intramolecular reactions of this type have been reported, but Piers et al. [139] have shown that the Stille couphngs can be used to form five-membered rings that link a bicyclic system and in doing so convert it to a tricychc system (Scheme 6.35). 

The Stille-coupHng-based polycondensations and copolymerizations are still among the most important methodologies for the synthesis of functional materials. The high level of functional group tolerance and the applied mild reaction conditions for the StiUe coupHng are very important features for the synthesis of functional oHgomers and polymers. This particular research area has recently been reviewed... 

A particularly nice application of the hydrostannylation is the Stille coupling (for reviews on the Stille couphng see [ 119-123]) that becomes catalytic in tin, as introduced by Maleczka and coworkers [124,125]. Terminal alkynes and organobromides can be coupled in the presence of catalytic amounts of tributyltinchloride and Pd(ll) and Pd(0) catalysts and stoichiometric amounts of PMHS (polymethylhydrosiloxane) to give the alkene derivatives 166-173 in good to excellent yields (Scheme 64). 

---