Dinitrogen ligands, chiral

For attempts to use chiral dinitrogen ligands in these reactions, see G. 

Figures 8E.3-8E.6 show a selection of some ligands that have been successfully used in the palladium-catalyzed AAA reaction. They are classified into four categories 1) chiral phosphines, 2) dinitrogen ligands, 3) P,N-chelate ligands, and 4) mixed chelate ligands. Although this...

Figure 3 Chiral dinitrogen ligands with fused hetero spiro backbone...

Significant recent interest in the transition metal catalyzed reactions of imidoiodanes was initiated in the 1990s by the pioneering works of Evans [586, 763, 764] and Jacobsen [765,766] on the asymmetric aziridination of olefins using copper catalysts (2-10 mol%) with chiral dinitrogen ligands and PhD JTs as the nitrene precursor. Since these initial publications, research activity in this area has surged and the copper-catalyzed aziridination of alkenes has been utilized in numerous syntheses. For example, Dodd and coworkers applied the Evans aziridination procedure to 2-substituted acrylates and cinnamates 649 [767] and to steroids 650 (Scheme 3.257) [768]. 

Particularly important are enantioselecUve aziridinations of alkenes using PhINTs and copper catalysts with chiral dinitrogen ligands [777-781]. In a representative example, the PhINTs-promoted asymmetric aziridination of alkene 655 affords chiral aziridine 656 with excellent enantioselectivity (Scheme 3.260) [777]. 

Chiral Rh(II) oxazolidinones Rh2(BNOX)4 and Rh2(IPOX)4 (25a,b) were not as effective as Rh2(MEPY)4 for enantioselective intramolecular cyclopropanation, even though the steric bulk of their chiral ligand attachments (COOMe versus i-Pr or CH2Ph) are similar. Significantly lower yields and lower enantioselectivides resulted from dinitrogen extrusion from prenyl diazoacetate catalyzed by either Rh2(4.S -lPOX)4 or Rh2(4S-BNOX)4. This difference, and those associated with butenolide formation [91], can be attributed to the ability of the carboxylate substituents to stabilize the carbocation form of the intermediate metal carbene (3b), thus limiting the Rh2(MEPY)4-catalyzed reaction to concerted carbene addition onto both carbon atoms of the C-C double bond. 

The use of chiral dirhodium carboxylate, 17 or 18, is preferred over chiral dirhodium carboxamidates for chemical transformations of a-diazo-p-ketocarbonyl compounds primarily because of reactivity considerations, that is, these diazo compounds do not undergo dinitrogen loss with the carboxamidate catalysts even at elevated temperatures. In addition, the orientation of the chiral ligands in 17 and 18 provides closer access to bulky diazo compounds. When the two attachments to the di azomethane unit are vastly unequal in size, high levels of enantiocontrol can result. 

Other procedures for carbonyl hydrosilylation of aldehydes and ketones are using [bis(imino)pyridine]iron dinitrogen and dialkyl complexes as precatalysts. Only 0.1-1.0 mol% catalyst are required to achieve this transformation. The reductants are either phenylsilane or diphenylsilane in this case. A number of enantioselective versions of the hydrosilylation reaction is described. This includes the application of 1,2-bis[(25, 55)-2,5-dimethylphospholano]benzene [(S,5)-Me-DuPhos] (Scheme 4-328) as chiral ligand, iron(II) acetate as a precatalyst and polymethylhydrosiloxane as hydride source. A large variety of ketones can be transformed into the corresponding alcohols in excellent yield and up to 99% enantiomeric excess. Catalytic ketone hydrosilylation is also achieved with the dialkyliron complexes (S,S)-... 

Dinitrogen-fused heterocycles have been formed in high yield by thermal 3-1-2-cycloadditions of two types of azomethine imines with allenoates. Rhodium-catalysed formal 3 -l- 2-cycloadditions of racemic butadiene monoxide with imines in the presence of a chiral sulfur-alkene hybrid ligand have furnished spirooxindole oxazolidines and 1,3-oxazolidines stereoselectively. ° Formation of 1,2-disubstimted benzimidazoles on reaction of o-phenylenediamine with aldehydes is promoted by fluorous alcohols that enable initial bisimine formation through electrophilic activation of the aldehyde. 

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