Scope and Mechanistic Analysis of the Enantioselective Synthesis of Allenes by Rhodium-Catalyzed Tandem Ylide Formation/[2,3]-Sigmatropic Rearrangement between Donor/Acceptor Carbenoids and Propargylic Alcohols,Journal of the American Chemical Society

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Scope and Mechanistic Analysis of the Enantioselective Synthesis of Allenes by Rhodium-Catalyzed Tandem Ylide Formation/[2,3]-Sigmatropic Rearrangement between Donor/Acceptor Carbenoids and Propargylic Alcohols
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2012-09-11 , DOI: 10.1021/ja3061529
Zhanjie Li ₁ , Vyacheslav Boyarskikh , Jørn H Hansen , Jochen Autschbach , Djamaladdin G Musaev , Huw M L Davies

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Rhodium-catalyzed reactions of tertiary propargylic alcohols with methyl aryl- and styryldiazoacetates result in tandem reactions, consisting of oxonium ylide formation followed by [2,3]-sigmatropic rearrangement. This process competes favorably with the standard O-H insertion reaction of carbenoids. The resulting allenes are produced with high enantioselectivity (88-98% ee) when the reaction is catalyzed by the dirhodium tetraprolinate complex, Rh(2)(S-DOSP)(4). Kinetic resolution is possible when racemic tertiary propargylic alcohols are used as substrates. Under the kinetic resolution conditions, the allenes are formed with good diastereoselectivity and enantioselectivity (up to 6.1:1 dr, 88-93% ee), and the unreacted alcohols are enantioenriched to 65-95% ee. Computational studies reveal that the high asymmetric induction is obtained via an organized transition state involving a two-point attachment: ylide formation between the alcohol oxygen and the carbenoid and hydrogen bonding of the alcohol to a carboxylate ligand. The 2,3-sigmatropic rearrangement proceeds through initial cleavage of the O-H bond to generate an intermediate with close-lying open-shell singlet, triplet, and closed-shell singlet electronic states. This intermediate would have significant diradical character, which is consistent with the observation that the 2,3-sigmatropic rearrangement is favored with donor/acceptor carbenoids and more highly functionalized propargylic alcohols.

中文翻译：

通过铑催化串联叶立德形成/[2,3]-供体/受体类卡宾醇和炔丙醇之间的Sigmatropic重排对联烯的对映选择性合成的范围和机理分析

炔丙基叔醇与甲基芳基乙酸酯和苯乙烯基重氮乙酸酯的铑催化反应导致串联反应，包括氧鎓叶立德形成，然后是 [2,3]-σ 重排。该过程与类卡宾的标准 OH 插入反应相得益彰。当反应由四脯氨酸二铑配合物 Rh(2)(S-DOSP)(4) 催化时，生成的丙二烯具有高对映选择性 (88-98% ee)。当外消旋叔炔丙醇用作底物时，可以进行动力学拆分。在动力学拆分条件下，形成的丙二烯具有良好的非对映选择性和对映选择性（高达6.1:1 dr，88-93% ee），未反应的醇被对映体富集到65-95% ee。计算研究表明，高不对称诱导是通过涉及两点连接的有组织的过渡态获得的：醇氧与类卡宾之间的叶立德形成以及醇与羧酸盐配体的氢键合。2,3-sigmatropic 重排通过 OH 键的初始裂解进行，生成具有紧密开壳单线态、三线态和闭壳单线态电子态的中间体。该中间体将具有显着的双自由基特征，这与供体/受体类卡宾和更高度官能化的炔丙醇有利于 2,3-σ 重排的观察结果一致。醇氧和类卡宾之间的叶立德形成以及醇与羧酸盐配体的氢键。2,3-sigmatropic 重排通过 OH 键的初始裂解进行，生成具有紧密开壳单线态、三线态和闭壳单线态电子态的中间体。该中间体将具有显着的双自由基特征，这与供体/受体类卡宾和更高度官能化的炔丙醇有利于 2,3-σ 重排的观察结果一致。醇氧和类卡宾之间的叶立德形成以及醇与羧酸盐配体的氢键。2,3-sigmatropic 重排通过 OH 键的初始裂解进行，生成具有紧密开壳单线态、三线态和闭壳单线态电子态的中间体。该中间体将具有显着的双自由基特征，这与供体/受体类卡宾和更高度官能化的炔丙醇有利于 2,3-σ 重排的观察结果一致。

更新日期：2012-09-11

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