Palladium chemistry leaving groups

The invention of the triflate (trifluoromethylsulfonyl) group — one of the world s best leaving groups — has led to its use in palladium chemistry [42]. Conway and Gribble described the synthesis of 3-indolyl triflate 34 [12] and 2-indolyl triflate 35 from oxindole [43]. Mdrour synthesized the N-phenylsulfonyl derivative 36 by employing a Baeyer-Villiger oxidation of the appropriate indolecarboxaldehyde [44],... 

Leaving groups in the Tsuji-Trost reaction include acetates, halides, ethers, carbonates, sulfones, carbamates, epoxides, and phosphates. Reviews (a) Tsuji, J. In Handbook of Organopalladium Chemistry for Organic Synthesis, Negishi, E. deMeijere, A., Eds. Wiley-lnterscience New York, 2002 Vol II, Palladium-Catalyzed Nucleophile Substitution Involving Allyl Palladium, Propargyl-palladium and Related Derivatives, pp. 1669-1687. (b) Frost C. G. Howarth, J. Williams, J. M. J. Tetrahedron Asymmetry 1992, 3, 1089-1122. 

A different approach to the cephalotaxine ring system also used tf-allyl palladium chemistry (Scheme 9.49). " Tetramethylguanidine (TMG), which is a stronger base than triethylamine by at least two orders of magnitude, was found to be the base of choice for the cyclization of allylic sulfone 9.171. The sulfone leaving group was also essential to the synthesis of the earlier intermediate 9.170 by allowing alkylation to introduce the aminopropyl side chain. ... 

After it had been shown that the chemistry of preformed enolates is compatible with that of catalytically generated allylpalladium complexes, the question of the stereochemical course of these transformations came up. For the attack of a carbon nucleophile to a it-allylpalladium complex 57, two paths have to be discussed the outer-sphere mechanism involves the approach of the nucleophile from the face opposite of the transition metal. The inner-sphere mechanism postulates a precoordination of palladium and the nucleophile leading to 59, followed by a bond-forming reaction by reductive elimination. As a consequence, the nucleophile approaches from the face that is occupied by palladium. Given that, in the precedent step, the leaving group of the allylic substrate 56 has been replaced by the transition metal under inversion, the outer-sphere mechanism leads to a net retention (product 58), whereas the inner-sphere path results in net inversion (product ent-58) (Scheme 5.20). It was generally accepted that soft nucleophiles... 

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