Total Synthesis of 3‐Oxo‐ and 3β‐Hydroxytauranin via Negishi Coupling of a Bis(ortho‐oxy)‐Functionalized Benzyl Chloride

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AbstractThe first asymmetric synthesis of the sesquiterpene quinones 3‐oxo‐ and 3β‐hydroxytauranin (1, 2) was achieved and the originally proposed structure of 3α‐hydroxytauranin was revised. The protected benzyl chloride 5 was obtained in six steps starting from 4‐bromo‐3,5‐dihydroxybenzoic acid (8) via a highly scalable approach. The troublesome Negishi coupling of the benzyl chloride 5 with alkenyldimethylalane 6 was optimized to furnish all‐trans‐farnesylarene 14 in very good yield. This prenylated arene was transformed in six additional steps to 3β‐hydroxytauranin (2). Finally, a new convenient access to propargylated terpenes without using dry cryogenic ammonia and gaseous allene or propyne is described.