255828-88-7Relevant articles and documents
Asymmetric Acylation of sec-Alcohols with Twisted Amides Possessing Axial Chirality Induced by the Adjacent Asymmetric Center
Yamada, Shinji,Katsumata, Hiroko
, p. 9365 - 9373 (2007/10/03)
This paper reports that axially chiral twisted amides serve as asymmetric acylating agents for sec-alcohols under neutral conditions. Kinetic resolution of various racemic sec-alcohols and desymmetrization of 1,2-, 1,3-, and 1,4-meso-diols were performed by using the twisted amides. The utility of this desymmetrization method was shown by the preparation of the synthetic intermediate 28 for macrolide antibiotic nodusmicin and 18-deoxynargenicin. The stereoselectivity of the acylation reactions is significantly dependent on the bulkiness of both the acyl group and the C-4 substituent of the chiral auxiliary. When an amide possessing an imidazolyl group at C-4 was employed, the stereoselectivity was reversed to give R esters. A possible working model of the acylation reaction is also described on the basis of the structural studies of the twisted amides by IR and 1H and 13C NMR spectroscopies and AMI calculations. These studies suggested that rotamer II is thermodynamically more stable than the others. The rotamer II has an axial chirality about its C(O)-N linkage that is induced by the adjacent chiral center. This would enable discrimination of the two enantiomeric hydroxy groups of the racemic alcohols or meso-diols.
