A total synthesis of bruceantin (1) using 15-deoxybruceolides 9 and 43 derived from naturally occurring brusatol as relay compounds was achieved. Previously reported ABCE tetracyclic compound 16 was converted into 11,12-cis-diol 30 bearing a suitable oxygen function at C-7. Ring D (δ-lactone) was formed by oxidation of a hydroxyl group at C-16 and selective removal of a C-7 hydroxyl protecting group to give 36. Inversion of the stereochemistry of the hydroxyl group at C-11 was done by selective oxidation and reduction to give 12. Enolate oxidation of the C-3 carbonyl group of 40, which was derived from 12, followed by bismuth trioxide oxidation yielded (±)-15-deoxybruceolide derivative 42, which was further converted into acetate (±)-43 and TBS ether (±)-9. Authentic specimens of 9,42, and 43 were derived from naturally occurring brusatol (3) by using a radical-mediated deoxygenation of phenyl thiocarbonate 46. Oxygenation at C-15 was achieved by oxidation of vinyl ethers 52 and 67. Esterification of the C-15 hydroxyl group followed by acid-catalyzed hydrolysis of protecting groups at C-3, -11, and -12 gave bruceantin (1).
ASJC Scopus subject areas
- Organic Chemistry