Collect. Czech. Chem. Commun.
1991, 56, 2917-2935
https://doi.org/10.1135/cccc19912917
An unusual reaction of a bridged triterpenoid α-diketone with acetic anhydride
Eva Klinotováa, Václav Křečeka, Jiří Klinota, Miloš Buděšínskýb, Jaroslav Podlahaa, Jana Podlahováa and Jiří Ječnýc
a Department of Chemistry, Charles University, 128 40 Prague 2
b Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6
c Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6
Abstract
3β-Acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) reacts with acetic anhydride in pyridine under very mild conditions affording β-lactone IVa and γ-lactones Va and VIIa as condensation products. On reaction with pyridine, lactones Va and VIIa undergo elimination of acetic acid to give unsaturated lactones VIIIa and IXa, respectively. Similarly, the condensation of 20β,28-epoxy-21,22-dioxo-18α,19βH-ursan-3β-yl acetate (IIIb) with acetic anhydride leads to β-lactone IVb and γ-lactone Vb; the latter on heating with pyridine affords unsaturated lactone VIIIb and 21-methylene-22-ketone Xb. The structure of the obtained compounds was derived using spectral methods, particularly 1H and 13C NMR spectroscopy; structure of lactone IVa was confirmed by X-ray diffraction.
