Two chiral quaternary carbon-containing fragments suitable for elaboration to the briaran diterpenes were obtained by regioselective methylation of functionalized 3, 3-disubstituted 2, 3-epoxy-1-ols. The factors which favor methylation at the more hindered position of a trisubstituted 2, 3-epoxy alcohol were determined.
![(R)-3-(((1R,3R,3aS,3bR,5aS,6aR,8S,10aR,11aS,11bS,13aR)-3,3a-dihydroxy-11a,13a-dimethyl-9-oxo-1-(5-oxo-2,5-dihydrofuran-3-yl)octadecahydro-1H-cyclopenta[7,8]phenanthro[2,3-b][1,4]dioxin-8-yl)oxy)butanal结构式](https://image.chemsrc.com/caspic/059/77356-33-3.png)