Chiral anionic reagents

NMR. These chiral anionic reagents are diamagnetic, thus avoiding broadening of the peaks in the NMR spectra, which is not the case, as we shall see, with certain chiral lanthanide complexes used as chemical shift agents. 

Likewise, the same BINPHAT anion acts as an efficient NMR shift reagent for quaternary ammonium cations (182-186) including the biologically active methacoline (187). Furthermore, the BINPHAT anion has been shown to be an efficient NMR chiral shift reagent for triphenylphosphonium salts containing stereogenic centres on an aliphatic side chain, e.g. (188ab) and (189). ... 

In a variation on the same theme, a novel C2-symmetric hexacoordinated phosphorus cation (191) was synthesized from tropolone (190), R-BINOL and PCI5 and shown to be an efficient NMR shift reagent for chiral anionic phosphate (e.g. BINPHAT, Figure 2) and borate anions. 

Lanthanide complexes with optically active -diketones have been used to determine the purity of optical isomers see chap. 4, p. 87 of Ref. 2 for a review). The most widely used chiral shift reagents are based on 3-trifiuoroacetyl-d-camphor, the anion of which is designated facam. The crystal structure determination of the DMF adduct of tris(3-tri-fiuoroacetyl-d-camphorato) praseodymium (III), the first of a chiral shift reagent, has been completed (31). The asymmetric unit contains the dimer, (facam)sPr(DMF)3Pr(facam)3, with the DMF oxygen atoms forming bridges between the two Pr(facam)3 moieties. Therefore, each Pr(III) ion is nine-coordinate with a geometry best described as a capped... 

Ge(CH3)3CD(OH)CgH5 (Table 24, No. 29). The anionic rearrangement after metallation proceeds with 98% inversion of configuration at carbon. The isotope ratio k(H)/k(D) is over 25. The NMR spectrum of the compound in the presence of a chiral shift reagent showed four CH3Ge resonances [43]. 

Hanessian resolved alkylqrclohexanones by benzylidenation with a chiral olefination reagent arising from R,R)-103 [71]. Treatment of ( )-2-methylcyclohexanone 104 with 0.5 Molar equiv of the anion of 103 gave ( ,2S)-(2-methylcyclohexane)-benzylidene 105 (together with <2% of the Z-isomer), in 34% yield, based on the ketone (63% based on the chiral reagent). Analogously, ( )-cts-2,4-dimethylcyclohexanone 106 afforded the 3-hydroxyphosphonamide 107, then the ( ,2R,4i )-(2,4-dimethylcyclohexane)-benzylidene 108 in 30% yield and over 99% ee. 

In a similar way, racemic 3-substituted cyclohexanones 121 were reacted with the anion of the chiral phosphoamidate reagent 18a to give two isomeric optically active alkenes, that is (S, ) and (i , Z)-alkenes possessing the opposite absolute configuration at the homoallylic carbon centers, with high enantiomeric excess [55]. 

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