Semisynthesis of (−)-Barbatusol, (+)-Demethylsalvicanol, and (+)-Rosmaridiphenol from (+)-Pisiferic Acid

Abstract

(+)-Pisiferic acid (1) was converted into (+)-12-O-methoxymethylpisiferol (5c) in 3 steps. The rearrangement of 5c with trifluoromethanesulfonic anhydride in pyridine provided (−)-12-O-methoxymethylpisiferin (6c), which was converted into icetexane phenols 6a, 11, and 14. The ortho-selective oxygenation of 6a and 14 with stabilized 2-iodoxybenzoic acid (SIBX), followed by the reduction of intermediary quinones afforded (−)-barbatusol (2) and (+)-rosmaridiphenol (4) in 49% and 35%, respectively. The oxygenation of 11 using potassium 5-methyl-2-iodobenzenesulfonate (pre-MIBS) with Oxone® followed by reduction gave (+)-demethylsalvicanol (3) in 59% yield.