The synthesis of (S)-(−)-rosmarinic acid (30) in 9% overall yield is described. The synthesis was achieved by a convergent route in which 3-(3′,4′-dihydroxyphenyl)-(S)-lactic acid (23) and caffeic acid (25), both appropriately protected, were coupled to produce a pentaallyl precursor 29, which was then deprotected to give (S)-(−)-rosmarinic acid (30). A triallyl derivative 35 was similarly prepared and converted to (+)-rabdosiin (41) and its (1R,2S) isomer (42) via a biomimetic oxidative free radical coupling–cyclization followed by deallylation. The coupling–cyclization gave a ratio of rabdosiin diastereomers unlike that found in nature. A preliminary study showed that methyl (R)-mandelyl sinapate (15) could be dimerized diastereoselectively to give a 1,2-trans thomasidioate diester (16). Keywords: rabdosiin, rosmarinic acid, lignan, oxidative coupling.

中文翻译：

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(S)-(-)-迷迭香酸的非酶法合成和对(+)-rabdosiin的仿生途径的研究

描述了以 9% 总产率合成 (S)-(-)-迷迭香酸 (30)。该合成是通过收敛途径实现的，其中 3-(3',4'-二羟基苯基)-(S)-乳酸 (23) 和咖啡酸 (25)，两者均得到适当保护，偶联产生五烯丙基前体 29 ，然后将其脱保护以得到 (S)-(-)-迷迭香酸 (30)。类似地制备了三烯丙基衍生物 35，并通过仿生氧化自由基偶联-环化，然后去烯丙基化转化为 (+)-rabdosiin (41) 及其 (1R,2S) 异构体 (42)。偶联-环化产生了不同于自然界中发现的 rabdosiin 非对映异构体的比例。初步研究表明，(R)-扁桃酸甲酯 (15) 可以非对映选择性地二聚化，得到 1,2-反式 thomasidioate 二酯 (16)。关键词：rabdosiin，迷迭香酸，木脂素，