Briarellin diterpenes

During the first total synthesis of briarellin diterpenes, briarellins E and F, L.E. Overman and co-workers utilized the large reactivity difference between a triple and a double bond in peroxyacid oxidations to selectively epoxidize a trisubstituted double bond in the presence of a terminal alkyne." The epoxidation with mCPBA was carried out in DCM in the presence of a base to afford the a-epoxide in a 9 1 diastereomeric ratio. 

The Prins-pinacol rearrangement was utilized during the first enantioselective total synthesis of briarellin diterpenes by L.E. Overman and co-workers. The cyclohexadienyl diol substrate was condensed with a (Z)-a,p-unsaturated aldehyde at low temperature in the presence of catalytic amounts of acid and MgS04 as dehydrating agent. The initially formed acetal was then exposed to 10 mol% of SnCU to afford the desired tetrahydroisobenzofuran as a single stereoisomer that was later converted to briarellin F. 

Corminboeuf, O., Overman, L.E., and Pennington, L.D. (2009) A unified strategy for enantioselective total synthesis of cladiellin and briarellin diterpenes Total synthesis of briarellins E and F and the putative stmcture of alcyonin and revision of its stmcture assignment. J. Org. Chem., 74, 5458-5470. 

Briarellins are a class of eunicellin diterpenes isolated from the gorgonians Pachyclavularia violacea and Briareum polyanthes [88]. 

Briarellins J-P and polyanthellin A New eunicellin-based diterpenes from the gorgonian coral Briareum polyanthes and their antimalarial activity./. Nat. Prod., 66, 357-363. 

---