A general and practical method for the synthesis of sulfonylated cinchona alkaloids
is presented. The reactions are carried out via Zn-mediated nucleophilic aromatic
substitution of the N-oxides of the quinoline core in cinchona alkaloids with a range of sulfonyl chlorides.
By careful optimization of the reaction parameters and the procedure, both aromatic
and aliphatic sulfonyl chlorides react efficiently with the N-oxides to afford the corresponding sulfonylated products in high yields. In addition,
the reaction can be reliably scaled up to gram level. As a result, this method provides
a practical route for the synthesis of new cinchona alkaloid derivatives that might
be potentially useful compounds, particularly in asymmetric catalysis.
Key words
cinchona alkaloids - quinoline
N-oxides - quinolines - sulfonylation - nucleophilic aromatic substitution