Efficient Total Synthesis of (−)-Ilimaquinone

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Abstract
The total synthesis of (−)-ilimaquinone, a metabolite isolated from sea sponges, is described. The key step of the synthesis is the attachment of the quinone moiety to the drimane skeleton. Alkylation of enone 11 obtained in four steps from the readily available diketone 8, with tetramethoxybenzyl bromide 15 as the alkylating agent, led to addition product 16 in excellent yield. The presence of the tetramethoxybenzyl group induced stereoselective hydrogenation of the exo olefin 18, leading to the required isomer in a 9:1 ratio. Treatment of compound 21 with ceric ammonium nitrate (CAN) afforded formation of the quinone and deprotection of only one methyl ether in one step to furnish the desired ilimaquinone 1.