47 (±)-Sanadaolの全合成

概要

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The first total synthesis of (±)-sanadaol, structurally unique marine diterpene isolated from brown algae Pachydictyon coriaceum and Dictyota crenurata, is described. The key step of this fully stereocontrolled synthesis involves the fragmentation reaction of tricyclic compound 15 forming bicyclic compound 16 having suitably functionalised framework of sanadaol as shown in the synthetic strategy (Fig 1). Synthesis of the key intermediate 15 was accomplished by the route shown in Scheme 1. Sequential Michael reaction of the kinetic enolate of enone 3 with ethyl solvate gave bicyclo[2.2.2]octane 4 which was then converted into keto ester 7 by 9-step sequence. Intramolecular Michael reaction of 7 with catalytic amount of t-BuOK afforded tricyclic ketone 8 having correct configuration at C(3). Stereoselective α-methylation of the ester group in 8 was achieved through lactone 11. The methylated lactone 12 was transformed into the key intermediate 15 via diol ester 13 and diol 14. Conversion of the key intermediate into (±)-sanadaol was done by the process shown in Scheme 2. Cleavage of C(1)-C(5) bond in 15 using sodium hydride and small amount of 15-crown-5 gave keto olefin 16 having bicyclo[4.3.1]decane ring system. Elaborative adjustment of functionality in 16 led to (±)-sanadaol.
天然有機化合物討論会の論文
1986-09-09