Reactivity Enhancement for Chiral Dirhodium(II) Tetrakis(Carboxamidates)

Abstract

Difluorinated ligands from azetidinone‐4‐carboxylates and pyrrolidinone‐5‐carboxylate have been prepared, substituted onto dirhodium(II), and the reactivities and selectivities of the resulting catalysts have been examined. The fluorinated catalysts exhibit enhanced reactivity towards diazo decomposition but diminished enantioselectivities for cyclopropanation. Selectivity for ylide formation and rearrangement or Si‐H insertion is enhanced or similar to that with unfluorinated analogues.

Lithium Enolates Derived from Pyroglutaminol: Aggregation, Solvation, and Atropisomerism

“…1,2 These stereochemically rich, nitrogen-based synthons contain critical features that allow for stereocontrolled functionalizations of both the α and the β carbons. Reactions that exploit the chirality of these compounds include alkylations, 3,4 aldol and aza-aldol additions, 5,6 and halogenations 7,8 of enolates as well as 1,4-additions, 9,10 cycloadditions, 11 dihydroxylations, 12 and cyclopropanations 13,14 of the analogous α, β-unsaturated lactam. The stereocontrol is often unremarkable; however, compared with the more popular benzylidene analog 1a , the acetonide-protected variant 1b enhances the preference for functionalization from the convex face.…”

Rhodium(II)‐Catalyzed 1,3‐Dipolar Cycloaddition Reactions

“…In this series, rhodium(II) trifluoroacetamidate [Rh 2 (tfa) 4 ] was the first described [30]. The enhanced reactivity of the perfluorinated carboxamides was also observed by Doyle et al [34]; however, no increase in enantioselectivity was noted with the chiral variants of these catalysts. Subsequent studies using Rh 2 (tfa) 4 and the related rhodium(II) perfluorobutyramidate [Rh 2 (pfbm) 4 ] demonstrated an additional propensity for oxindole [31] and indole formation [32] via C-H insertion, in addition to the formation of isomünchnones [33].…”

“…Despite the potential dissociation of the rhodium(II) metal from newly formed dipoles, a number of the chiral rhodium(II) catalysts have been developed that demonstrated the ability to induce enantioselectivity in 1,3-diploar cycloaddition reactions (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34) [11,35,100,101]. One of the earliest examples of a chiral rhodium(II)-induced enantioselective cycloaddition was described by Pirrung and Zhang [102] using a novel bisnaphtholphosphate ligand-containing catalyst 22 in the construction of the dihydrofuro[2,3-b]furan ring system.…”

Selectivity in Rhodium(II)Catalyzed Reactions of Diazo Compounds: Effects of Catalyst Electrophilicity,Diazo Substitution, and Substrate Substitution. From Chemoselectivityto Enantioselectivity

“…57 Although these catalysts were significantly more reactive toward carbenoid generation, enantioselectivity suffered in the cyclopropanation of styrene. Rh 2 (4S-dFIBAZ) 4 gave more promising results for ylide generation and subsequent [2,3]-sigmatropic rearrangement than its nonfluorinated counterpart.…”