Stereochemical Control in Palladium‐catalyzed Allylic Etherification

Abstract

Abstract. Two alternative approaches for increasing the stereospecificity of Pd(0)-catalyzed allylic etherification are presented, both of which also suppress product isomerization and elimination. One of them involves addition of chlorotrimethylsilane to a benzene reaction mixture. In the model reaction studied, it increases the ratio of the two stereoisomeric products, arising from either retention or inversion of configuration at the allylic carbon, from 3:l to 9:1, respectively. The second approach involves the employment of both donor-and acceptor-chelating ligands. Essentially 100% stereospecificity (retentionof configuration) was achieved when the reaction was carried out in benzene at 60 O C in the presence of Pd&dba), and bis-1,2-diphenylphosphinoethane.

On the Nature of the Catalytic Palladium-Mediated Elimination of Allylic Carbonates and Acetates To Form 1,3-Dienes

“…The major concern in carrying out such a test of stereospecificity is the potential for palladium to scramble between the diastereomeric faces of the allyl system …”

“…The major concern in carrying out such a test of stereospecificity is the potential for palladium to scramble between the diastereomeric faces of the allyl system. 18 If scrambling were to occur, a mixture of 16 and 17 would be obtained regardless of any stereospecificity in the elimination step. Tsuji's observation that regioisomeric dienes are obtained from the reactions of diastereomeric allylic carbonates in certain rigid polycyclic ring systems 6 suggested that such scrambling is slow relative to elimination with the [Pd(OAc) 2 /PBu 3 ] catalyst system.…”

Palladium-Catalyzed Cross-Coupling between Allyl, Benzyl, or Propargyl Groups and Unsaturated Groups

“…The same stereochemistry has since been repeatedly observed with organozinc. [30], [32] Similar experiments with organotins pointing to the same conclusion were also reported later by Stille and coworkers. [33], [34] All of these investigations relied on diastereochemical relationships.…”

“…The retention of configuration in the C-C bond-forming step was also confirmed subsequently by the determination of absolute configurations, as shown in Scheme 13. [35] [31] Ph HOOC 90% 94% PhZnCl (2 equiv) Pd(0)L n [30], [32] OAc OAc OAc Ph cat. Pd(PPh 3 ) 4…”

Stereoselective Intramolecular Cyclization of Allyl and Homoallyl Benzamide via π-Allylpalladium Complex Catalyzed by Pd(0)

“…The palladium(0)-catalyzed allylation of nucleophiles (the Tsuji−Trost reaction) is a highly accepted synthetic method due to its broad applicability and facile experimental procedure . The catalytic cycle requires the formation of the cationic π-allylpalladium(II) complex, an intermediate which can be attacked by nucleophiles at the allylic system …”