Total synthesis of (+)-perrottetianal A

The total synthesis of (+)-perrottetianal A, one of the sacculatane-type diterpenes isolated from liverworts, has been achieved starting from an optically active Wieland–Miescher ketone analogue. The ethylene glycol monoacetal of the starting material was converted into the trans-decalone containing the required C-5 and -8a reactant groups via an eight-step reaction sequence. After introduction of a methyl group and then transformation of the angular hydroxymethyl functionality to the protected aldehyde group, an additional α,β-unsaturated formyl group was introduced by Nozaki and Yamamoto's method to give the corresponding C-8a monoacetal. Finally, hydrolysis of the acetal furnished (+)-perrottetianal A, which established the absolute configuration as (4aS, 5S, 8aR).