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A short and concise asymmetric synthesis of hamigeran B

机译：短而简明的不对称B合成人

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摘要

The interesting biological properties of the hamigerans wherein hamigeran B is a potent antiviral agent with low cytotoxicity to host cells make these deceptively simple looking structures challenging synthetic targets. A strategy to hamigeran B evolved wherein the three contiguous stereo-centers are established ultimately from a Pd catalyzed asymmetric allylic alkylation (AAA). The latter involves an asymmetric allylation of a non-stabilized ketone enolate in 77 % yield and 93 % ee. By using this process, (S)-5- allyl-2-isopropyl-5-methyl-1-trifluoromethanesulfonyloxycyclopentene becomes available in four steps from 2-methylcyclopentanone. Introduction of the aryl unit by cross-coupling proceeded intermolecularly but failed intramolecularly. On the other hand, reductive removal of the triflate permitted a Heck reaction to effect intramolecular introduction of the aryl ring. The unusual conformational properties of this molecular architecture are revealed by the regioselectivity of the beta-hydrogen elimination in the Heck reaction and the diastereoselectivity of the reduction establishing the stereochemistry of the carbon bearing the isopropyl group. The successful route consists of 15 steps from 2-methylcyclopentanone and dimethylorcinol illustrating the efficiency of the route based upon the Pd AAA.
机译：梭菌的有趣的生物学特性，其中梭菌B是对宿主细胞具有低细胞毒性的有效抗病毒剂，使这些看似简单的结构挑战了合成靶标。进化出了一种对人链球菌B的策略，其中三个连续的立体中心最终由Pd催化的不对称烯丙基烷基化（AAA）建立。后者涉及未稳定化的酮烯酸酯的不对称烯丙基化，产率为77％，ee为93％。通过使用该方法，从2-甲基环戊酮分四个步骤得到（S）-5-烯丙基-2-异丙基-5-甲基-1-三氟甲磺酰氧基环戊烯。通过交叉偶联引入芳基单元在分子间进行，但在分子内失败。另一方面，三氟甲磺酸酯的还原去除允许Heck反应实现芳基环的分子内引入。通过Heck反应中β-氢消除的区域选择性和还原的非对映选择性建立了带有异丙基的碳的立体化学，揭示了这种分子结构的不同构象性质。成功的路线由2-甲基环戊酮和二甲基甲酚组成15个步骤，阐明了基于Pd AAA的路线的效率。

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