Synthesis of axially chiral bipyridine <em>N</em>,<em>N'</em>‑dioxides and enantioselective allylation of aldehydes

Kotora, Martin

doi:10.1351/PAC-CON-09-10-01

Pure Appl. Chem., 2010, Vol. 82, No. 9, pp. 1813-1826

http://dx.doi.org/10.1351/PAC-CON-09-10-01

Published online 2010-06-07

Synthesis of axially chiral bipyridine N,N'‑dioxides and enantioselective allylation of aldehydes

Martin Kotora^1,2

¹ Department of Organic and Nuclear Chemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 128 43 Praha 2, Czech Republic
² Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo n. 2, 166 10 Praha 6, Czech Republic

Abstract: N-oxides possessing the pyridine framework are strong Lewis bases that can activate the C–Si bond of allylhalosilanes to such an extent that they catalyze reactions with aldehydes. N-oxides embedded in chiral scaffolds are usually capable of highly selective chirality transfer to the derived products. Our goal was to develop a general synthetic method allowing the preparation of structurally varied N,N'-dioxides suitable for enantioselective organocatalysis. The underlying synthetic strategy was based on [2 + 2 + 2]-cyclotrimerization of suitably substituted diynes with nitriles catalyzed by Co-complexes to generate the desired bipyridines, their further oxidation and resolution of which furnished the corresponding chiral N,N'-dioxides. The prepared compounds were used in catalytic allylation of aromatic aldehydes to homoallyl alcohols with high enantioselectivity (up to 96 % ee). Enantioselectivity, enantiodiscrimination, and the reaction mechanism are controlled by the choice of solvent.