described using triphenylmethanol in the presence of tris(pentafluorophenyl)borane (3 mol %) in dichloromethane at room temperature. The chemoselectivity of this protocol is demonstrated by studying the tritylation of a primary alcohol in the presence of a secondary alcohol and also the mildness of this catalyst was studied with substrates containing acid labile protecting groups.
Studies aimed at enhancement of reactivity and enantioselectivity of a lithium ester enolate using a chiral tridentate lithium amide
作者:Mostafa Ahmed Hussein、Akira Iida、Kiyoshi Tomioka
DOI:10.1016/s0040-4020(99)00644-4
日期:1999.9
chiral amines 7–13 mediated the asymmetric condensation reaction of lithium ester enolate 2 with benzaldehyde p-anisidine imine 3 giving the corresponding β-lactam 4 in up to 75% ee. It became apparent that coexistence of 2 and chiral lithium amides derived from 7–13 is an important factor for the enhancement of the reactivity and enantioselectivity of 2.
A macrocyclic sulfate (MCS)‐based approach to monodisperse poly(ethyleneglycols) (M‐PEGs) and their monofunctionalized derivatives has been developed. Macrocyclization of oligo(ethyleneglycols) (OEGs) provides MCS (up to a 62‐membered macrocycle) as versatile precursors for a range of monofunctionalized M‐PEGs. Through iterative nucleophilic ring‐opening reactions of MCS without performing group