Synthesis and stereochemistry of (−)-rosiridol and (−)-rosiridin

The plant-derived monoterpenoids (−)-rosiridol and (−)-rosiridin can be assembled in an enantioselective manner via DIP–Cl reduction of a ketone precursor obtained by BCl3-mediated C–C coupling of prenyl stannane and an α,β-unsaturated C5 aldehyde. On the basis of Mosher analyses, the absolute stereochemistry 4S was assigned to (−)-rosiridol; this was confirmed by X-ray structure analysis of pentaacetylrosiridin. Glucosylation of (4S)-4-acetoxygeraniol proceeds under Koenigs–Knorr conditions in diethyl ether. (−)-Rosiridin was synthesized for the first time.