Chiral azacrown ether

The asymmetric Darzens condensation, which involves both carbon-carbon and carbon-oxygen bond constructions, was realized by use of the chiral azacrown ether 75als2,s ,ss and the quaternary ammonium salts derived from cinchona alka-loids159"621 under phase transfer catalyzed conditions. The a,p-epoxy ketone 80 (R=Ph) was obtained with reasonable enantioselectivity by the reaction of... 

Asymmetric a-hydroxylation of ketones 97 through phase transfer catalysis under alkaline conditions was realized by use of the Merck catalyst 7 (R=4-CF3, X=Br)[721 as well as the chiral azacrown ether 98[731 in conjunction with molecular oxygen, as shown in Scheme 30. The highest enantioselectivity of 79% ee was attained in the a-hydroxylation of the tetralone 100 by use of the Merck cata-... 

P. Bako, T. Kiss, L. Toke, Chiral Azacrown Ethers derived from D-Glucose as Catalysts for Enantioselective Michael Addition , Tetrahedron Lett. 1997, 38, 7259-7262. 

Scheme 2.60 Enantioselective Michael addition of 2-nitropropane to chalcone catalyzed by chiral azacrown ethers...

Hori, K., Tamura, M., Tani, K., Nishiwaki, N., Ariga, M. and Tohda, Y. Asymmetric Epoxidation Catalyzed by Novel Azacrown Ether-type Chiral Quaternary Ammonium Salts under Phase-transfer Catalytic Conditions. Tetrahedron Lett. 2006, 47, 3115-3118. 

Asymmetric epoxidation catalyzed by novel azacrown ether-type chiral... 

ASYMMETRIC EPOXIDATION CATALYZED BY NOVEL AZACROWN ETHER-TYPE CHIRAL QUATERNARY AMMONIUM SALTS UNDER PHASE-TRANSFER CATALYTIC CONDITIONS... 

ASYMMETRIC EPOXIDATION OF (E)-CHALCONE CATALYZED BY THE AZACROWN ETHER-TYPE QUATERNARY AMMONIUM SALT AS CHIRAL PTC... 

The azacrown ether-type chiral quaternary ammonium salts as chiral PTCs are easily prepared from BINOL in four steps. Remarkably, Table 6.10 shows that the good efficiency of asymmetric epoxidation of various chalcones can be achieved by adjustment of the length of the carbon chains on the nitrogen atom in the quaternary ammonium salts. 

Table 6.10 Asymmetric epoxidation of chalcones catalyzed by the azacrown ether-type quaternary ammonium salts as Chiral PTCs (see Figure 6.8).

Unsaturated acetals undergo a similar process when NiClj and a chiral phosphine 58 are added." The reaction of enones with diethylzinc is catalyzed by CuCOTf) which is coordinated to 59. Rubidium prolinate acts both as a base and chirality elicitor in reactions involving nitroalkanes, and an azacrown ether constructed out of sugar also induces the... 

Several, novel (R)-BINOL-based azacrown ethers (649) with donor side-arms were synthesised and applied for the first time as chiral catalysts in the asymmetric Michael addition of an A-protected iminemethylphosphonate (646) onto acrylonitriles, esters and amides (647), resulting in substituted... 

Besides the use of chiral ammonium salts as phase transfer catalyst, different azacrown ethers 51a-e derived from different sugars has been proposed as an alternative [52], For all systems the influence of the length of the chain on nitrogen atom was evaluated. For compounds 51a, b (glucose derivatives) the best results were obtained when was 2-hydroxyethyl. Whereas for compounds 51c-e, the best results were obtained for the corresponding 3-hydroxypropyl derivative. In neither case the enantiomeric excess was higher than 74%. 

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