Chiral auxiliaries mediator

Oxazolidones as Chiral Auxiliaries Chiral Auxiliary-Mediated Aldol-Type Reactions... 

Chiral Auxiliary-Mediated Asymmetric Synthesis in the Crystalline State... 

Piskunova and colleagues reported chiral auxiliary mediated asymmetric azirine 538 syntheses in good yields (74-82%) and with a de of 92% (equation 239). 

Asymmetric conjugate addition is a powerful method for the construction of ternary stereogenic centers. Erick Carreria of the ETH-Honggerberg, Zurich reports (Organic Lett. 2004,6,2281) the chiral-auxiliary mediated conjugate addition of alkynes to alkylidene malonate derivatives such as 1, to give, after hydrolysis and decarboxylation, the enantiomerically-enriched acid 3. 

A chiral auxiliary-mediated Reissert reaction has been demonstrated. Though the diastereomeric ratios are not as high as hoped, the conditions are simple and the products are easily separated by flash chromatography (Equation 63) <2005TL2983>. A catalytic version of the asymmetric Reissert reaction with quinolines, isoquinolines, and pyridines has been developed by Shibasaki and co-workers <2005PAC2047, 2004JA11808>. 

SPOS also benefited from other technical improvements such as the on-resin analytical methods [112], the capture-release purification technique [113], and hydrophobically assisted switching phase [114], Recently, chiral auxiliary-mediated 1,2-n.v-glycosylations were introduced to SPOS, allowing for the efficient and stereoselective assembly of oligosaccharides [115] (see Chapter 7). 

Most of the ionic chiral auxiliary-mediated reactions presented in Table 4 occur with very respectable ees, even at quite high conversions. The best of these in terms of overall optical and chemical yield is the reaction shown in entry 4, which gives an essentially quantitative GC yield of the 3-lactam photoproduct with an ee of 99%. For a variety of practical reasons, and because modem methods of analysis do not require large sample sizes, all but one of the reactions in Table 4 were carried out on a microscale (< 10 mg). The lone exception was reaction 4, which could easily be scaled up to the 500 mg level to afford an ee of 99% with an isolated chemical yield of 91 % [21 ]. This was done by irradiating the salt... 

Chiral auxiliary-mediated diastereoselective allylations of a-bromoglycine derivatives 65 have also been established. 8-Phenylmenthol has been successfully employed as a chiral auxiliary in glycine allylations (Eq. (13.19)) [29]. The captoda-tive radical intermediate generated in this reaction benefits from the observation that a-amino acid radicals prefer an s-cis geometry about the single bond, presum-... 

The chiral auxiliary mediated aza-Claisen rearrangement of /V-allylketcnc. V.O-acetals also allows the diastereoselective construction of quaternary carbon centers642. Butyllithium proved to be an unsuitable base for the neutralization step in this case because the increased steric hindrance at C-l causes C-2 nucleophilic addition to become competitive with C-l deprotonation. However, this problem can be overcome by the use of lithium tov-butoxide or lithium isopropoxide. This is shown for the achiral. V-allylketene A. O-aceta] precursor 8. 

Chiral Auxiliary Mediated Reactions. . Chiral Ligand Mediated Reactions. . . Asymmetric Center Mediated Reactions... 

Chiral Auxiliary Mediated Reactions Chiral Ligand Mediated Reactions. ... 

Swindell CS, Tao M (1993) Chiral Auxiliary-Mediated Asymmetric Induction in a Thermal Inverse Electron Demand Hetero-Diels-Alder Reaction - Enantioselective Synthesis of the Taxol A-Ring Side Chain. J Org Chem 58 5889... 

Chiral—auxiliary-mediated asymmetric synthesis of ruthenium polypyr-idyl complexes 13ACR2635. 

Chiral Auxiliary Mediated Asymmetric Ireland-Claisen Rearrangements 4.6.6.1 Chiral Clycolates... 

To date the most general chiral auxiliary mediated asymmetric Ireland-Claisen rearrangement is that of Corey et al. (Scheme 4.44) [47]. They found that treatment of crotyl propionates and related esters afforded good yields, diastereoselectivities and enantioselectivities of the pentenoic acid products. The rearrangements also occurred at significantly lower temperature than the silyl ketene acetals. A key advantage of the chemistry is that the chiral auxiliary attachment, Ireland-Claisen rearrangement, and auxiliary removal all occur in one pot. 

Saito, N., Katayama, T., Sato, Y. (2010). Asymmetric synthesis of y-siloxyenamides via chiral auxiliary-mediated diastereoselective coupling of ynamides, aldehydes, and silane by nickel catalyst. Heterocycles, 82, 1181-1187. 

Sultam-based chiral auxiliaries mediate the stereoselectivity of Diels-Alder reactions, and the reaction of various substituted furans with benzyne provided an insight into the... 

Chiral auxiliary-mediated diastereoselective synthesis is a widely applied alternative to enantioselective synthesis (Section 11.2), biosynthetic methods (Chapter 12) and resolution... 

Figure 11.33 Outline of the chiral auxiliary-mediated diastereoselective process...

Cheung, E., Netherton, M. R., Scheffer, J. R., and Trotter, J., Linearly conjugated benzocyclohexa-dienone photochemistry in the solid state ionic chiral auxiliary mediated asymmetric induction. 

The first, chiral auxiliary mediated, asymmetric synthesis of (+)-luciduline (160) has been accomplished from readily available materials in 14 steps (10% overall) with a high degree of stereocontrol (94). Key steps include an intramolecular Diels-Alder reaction of a chiral dihydropyridine, a subsequent retro-Mannich ring opening, and a novel cationic reductive cyclization reaction. The enantiopure dihydropyridone 164, prepared from the chiral 1-acylpyridinium salt 161, was converted to the 1,2-dihydro-pyridine 166. Intramolecular Diels-Alder reaction and subsequent reduction leads to 168, which, after retro-Mannich ring opening, is converted into the enecarbamate 171. The... 

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