Enantioselective synthesis of the tricyclic core of (+)-strigol

An enantioselective synthesis of the tricyclic core structure of (+)-strigol, a potent seed germination stimulant for root parasitic weeds, has been achieved from 2-iodo-4,4-dimethyl-2-cyclohexen-1-one in 14 steps. The key steps include a CBS reduction of an iodo enone to obtain a cyclohexenol derivative of high enantiomeric excess, regioselective epoxide ring opening with a Grignard reagent in a low-polarity solvent, highly diastereoselective addition of vinyllithium to a ketone, and Lewis acid-promoted installation an acetate unit onto a bicyclic allylic acetate intermediate.

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