Asymmetric organocatalysts alcohols

Alcohols, Phenols and Carboxylic Acids as Asymmetric Organocatalysts... 

Morita-Baylis-Hillman carbonates undergo an hydrolysis in the presence of the asymmetric organocatalyst, hydroquinidine[anthraquinone-l,4-diyl] diether, and Cap2 in aqueous iV,iV-dimethylacetamide, yielding the allylic alcohol Tracer studies using showed that water is the nucleophile in the hydrolysis reaction. It is... 

Carbery et al. also used the DMAP scaffold to develop the first hehcenoidal asymmetric organocatalyst, which proved to be a particularly selective acylation catalyst for the KR of secondary aryl alkyl alcohols [64]. Catalyst 67 offered good to excellent selectivity factors ranging from s = 17 to 116 at catalyst loadings as low as 0.5mol% (Scheme 41.18). 

The product of asymmetric amination, diamine 84, was reported to be able to catalyze asymmetric fluorination of a-branched aldehydes, yielding 1, 2-fluorine alcohols with up to 90% ee (Scheme 5.23) [44], Worthy to note that the chiral center of the catalyst is orientated on the nitrogen atom and it is the first example of asymmetric organocatalyst with enantiomeric nitrogen as the only source of chirality. 

Use of hydroxyacetone as donor in the asymmetric Mannich reaction led to the formation of optically active syn /i-amino alcohols bearing two stereogenic centers [22, 23], In the presence of 35 mol% L-proline as organocatalyst several types of syn / -amino alcohol syn-35 were successfully synthesized with enantioselectivity up to 99% ee and high diastereomeric ratio. For example, a high yield of 92%, a diaster-eomeric ratio of 20 1, and enantioselectivity >99% ee were observed by List et al. for formation of the syn yfi-amino alcohol 35a (Scheme 5.17) [23]. In addition to hydroxyacetone the methylated derivative methoxyacetone was also applied successfully in this reaction (93% yield, d.r. > 39 1, >99% ee). 

Bohn and co-workers also studied diethylzinc addition to benzaldehyde with soluble polymeric catalysts [10]. Dendritic chiral catalysts consisting of poly(benzyl ethers) and chiral pyridyl alcohols (3) were used as organocatalysts for the asymmetric C-C linkage reaction. The enantiocontrol by the dendritic systems was slightly lower than that of the parent pyridyl alcohols (2-3% drop in ee) but the conversion toward the chiral secondary alcohol was actually slightly higher for the largest dendritic catalyst (84% versus 80% yield after 3 h of reaction time). In more... 

The allylation of aldehydes provides a useful route to homoallylic alcohols. The most popular methods for achieving this in an asymmetric fashion are by the use of metal-based Lewis acid catalysts or using Lewis basic organocatalysts. ... 

Since the introduction of the first peptide organocatalyst in the 1980s, a considerable number of new peptide frameworks have been developed that are able to effectively catalyse several important transformations including alcohol esterifications, 1,4-conjugate additions, aldol reactions, Strecker synthesis, asymmetric cyanohydrin synthesis and alkene epoxidation are discussed. A few successful examples of solid-supported peptides and reactions in ball milling under solvent-free conditions have been demonstrated. These methods combine the advantages of being economically and environmentally friendly processes. 

High yields of 2-substituted chromans are readily attained from the asymmetric intramolecular oxa-Michael addition reaction of phenols bearing an (f -a,P-unsaturated ketone or thioester moiety mediated by a cinchona-alkaloid-urea-based bifunctional organocatalyst (140BC119). Molecular iodine-catalyzed reaction of phenols with a,P-unsaturated alcohols affords a wide range of 2,2-disubstituted chromans (14T5221). Chiral derivatives result from the intramolecular allylic alkylation of phenols bearing an... 

Surprisingly, asymmetric inductions became much more modest as soon as the catalyst deviated from these structural features. For example, Frejd et al. reported the synthesis of new organocatalysts based on a dibenzo-bicyclo[3.3.1]nona-2,6-diene framework (Scheme 24.13) that were tested in the same hetero-Diels-Alder reaction shown in Scheme 24.12. Although only modest, the best results were observed in the presence of the hydro g ketone 31 (up to 52% ee), which was more active than 30 or 32 and also than chiral monodentate alcohols (33, 34 and 35). The authors speculated that in the transition state there was the coordination of the aldehyde in a cleft in the... 

Maikov AV, Kabeshov MA, Bella M, Kysilka O, Malyshev DA, Plnhackova K, Kocovsky P (2007) Vicinal Amino Alcohols as Organocatalysts in Asymmetric Cross-Aldol Reactirai of Ketones Application in the Synthesis of Convolutamydine A. Org Lett 9 5473... 

The silyl ether of a elosely related 4-hydroxy-prolinamide alcohol was also successfully applied as an organocatalyst to the asymmetric aldolisation of either cyclic or acyclic ketones with a range of aromatic aldehydes in water. This catalyst was highly efficient and as low as 1 mol % of catalyst loading allowed high yields and excellent diastereo- and enantioselectivities to be obtained, as shown in Scheme 2.14. 

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