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Most Requested Journal Articles 2Q05-Chemistry and Related
Following is one of the journal articles most requested by researchers using CAS online services.
CAPLUS COPYRIGHT 2005 ACS on STN
A review. Eighteen years ago in Angewandte Chemie John K. Stille reviewed a novel methodol., which eventually became known by his name, for the coupling of organostannanes with org. electrophiles. The mechanism of the consecutive steps of the reaction, oxidative addn. of org. electrophile to Pd(0) complex, transmetalation, reductive elimination of biaryls are reviewed. Role of side reactions, such as scrambling of substituents and homocoupling is also considered. Effects of bidentate ligands, anions and palladium precursors is illustrated with several examples. Mechanism of transmetalation, including isolation of stable diorganopalladium species, enhancement of stannane reactivity by fluoride and hydroxide anions, is described in details. Very recent modifications are making synthetic wishes come true that were only dreamed of a few years ago. So-called "copper effect" ascribes the acceleration of the coupling reaction either to free phosphine scavenging by added CuI, or Sn-Cu transmetalation prior to formation of diorganopalladium intermediate. Use of N-heterocyclic carbenes as ligands allows substantial improvement in chemoselectivity and activity of palladium catalysts, suppressing undesired homocoupling and accelerating the reductive elimination step. In some cases, the Stille coupling proceeds via oxidative addn. of alkynylstannanes with Pd(0) complexes, with subsequent substitution of Pd-bound organotin group by aryl ligand. Moreover, as important advances are being made in the understanding of the mechanistic details of the process, it is becoming increasingly possible to apply this essential reaction and its new variants in a less empirical way.
Updated 5/8/2007 10:43:43 AM
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