SYNTHESIS OF 15-DEOXY-16-BETA-ETHOXYBRUCEANTIN AND SYNTHETIC EFFORTS TOWARD BRUCEANTIN

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.