Total Synthesis of (±)-Ramariolides C and D

Abstract

Ramariolides A–D (1–4) were isolated from the coral mushroom Ramaria cystidiophora, out of which 1 showed in vitro antimicrobial activity. The structural features of 1–4 are attractive synthetic targets. Here, we report the total synthesis of ramariolides C (3) and D (4). The vinylogous Mukaiyama aldol reaction was employed to construct the carbon skeletons of 3 and 4. The key precursors for the reaction were α-hydroxyaldehydes, which were prepared from cyanohydrins via reduction with diisobutylaluminum hydride (DIBAL). Successive acetylation of the aldol adducts and an elimination reaction of the resulting acetates yielded 3 and 4 upon treatment with tetra-n-butylammonium fluoride (TBAF) and acetic acid.