Ckf. Chiu et al., SYNTHESIS OF 15-DEOXY-16-BETA-ETHOXYBRUCEANTIN AND SYNTHETIC EFFORTS TOWARD BRUCEANTIN, Journal of organic chemistry, 59(2), 1994, pp. 311-323
Utilization of asymmetric Michael addition leads to chiral phenanthren
one (+)-4 suitable for the synthesis of Bruceantin. The D-ring is asse
mbled by means of an intramolecular alkylation of the bromoacetals 25
while only the axial diastereomer 25ax proceeds smoothly. The formatio
n of the cyanohydrin introduces the C-13 carborxyl group and tandem in
tramolecular alkylation provides the furan E-ring. The C-11,12 cis-dio
l 39 is readily transformed to the trans-diol 42 via an unusual Swern-
type oxidation/reduction sequence. The C-2,3 olefin proves to be an ef
ficient progenitor for the A-ring diosphenol function which can be int
roduced at the late stage of the synthesis. 15-Deoxy-16 beta-ethoxybru
ceantin 3 is accordingly prepared. Attempts to elaborate common interm
ediates toward the synthesis of bruceantin are described. The presence
of an oxygen function at C-15 drastically changes the relative reacti
vity of the C-2,3 and C-11,12 olefinic bonds.