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- Zincke aldehydes, or 5-aminopenta-2,4-dienals, are the product of the reaction of a pyridinium salt with two equivalents of any secondary amine, followed by basic hydrolysis. Using secondary amines (as opposed to primary amines) the Zincke reaction takes on a different shape forming Zincke aldehydes in which the pyridine ring is ring-opened with the terminal iminium group hydrolyzed to an aldehyde. The use of the dinitrophenyl group for pyridine activation was first reported by Theodor Zincke. The use of cyanogen bromide for pyridine activation was independently reported by W. König: The synthesis and utility of Zincke aldehydes has been reviewed. A variation of the Zincke reaction has been applied in the synthesis of novel indoles: with cyanogen bromide mediated pyridine activation (König method). More recently, an interesting rearrangement of Zincke aldehydes to Z-unsaturated amides was discovered serendipitously while trying to do an intramolecular Diels-Alder reaction. The rearrangement gives the Z-product stereospecifically. In a follow-up paper, allylic amines were used and gave products of a rearrangement / intramolecular Diels-Alder cascade. Mechanistic details were also discussed, however further investigations in collaboration with the Houk group revealed an unusual and unexpected mechanism based on computational studies. The new mechanism involves formation of a vinyl ketene. The Vanderwal group has also reported the synthesis of 4-stannyldienals from Zincke aldehydes by addition of tributylstannyl anion and quenching with acetyl chloride. The products are useful substrates for Stille cross-coupling reactions to give interesting polyene structures. In 2009, the Vanderwal group reported another interesting rearrangement of Zincke aldehydes. Tryptamine-derived Zincke aldehydes are heated with strong base to give the rearranged enal as shown below. This reaction was the key step in their total synthesis of norfluorocurarine, a Strychnos alkaloid. This strategy was also employed in a short synthesis of strychnine, becoming the shortest synthesis of strychnine reported to date at only six linear steps. This works has been highlighted on the blog Totally Synthetic. Also in 2009, the first reports of Zincke aldehydes undergoing a Pictet-Spengler reaction appeared from the group of Christian Marazano. This reaction provided the tetrahydro-β-carboline or tetrahydroisoquinoline core present in many alkaloid natural products, and was applied to the construction of a known intermediate in a previous total synthesis. One drawback of the Zincke Aldehyde synthesis is the need for 2 equivalents of the amine in the initial pyridine ring opening reaction. This is of particular concern for the case of complex secondary amines required for natural product synthesis. The group of Marazano recently found an alternative synthesis by condensation onto a variety of glutaconaldehyde derivatives using TFA. This solution has greatly simplified the production and purification of complex Zincke aldehydes. (en)
- Zincke醛（Zincke aldehydes）即5-氨基-2,4-戊二烯醛类，属于供体-受体双烯类（donor-acceptor dienes），是与两分子仲胺发生作用然后水解得到的产物。此反应与 Zincke 反应类似，不过仲胺的使用令吡啶发生开环，而且端位的亚胺离子基团被水解为醛，最终得到非环取代氨基烯醛。 使用二硝基苯基以活化吡啶环的技术最早是由 Theodor Zincke 报道的。 以溴化氰活化吡啶环的方法则是由 W. König 分别报道。 相关综述： Zincke 反应的一个变体最近（Vanderwal 2006）被用于新颖吲哚衍生物的合成。其中以溴化氰作为吡啶环的活化试剂。 2008年，Steinhardt 等在试图作时，偶然发现 Zincke 醛可在加热的条件下，以较高的立体选择性重排为相应的 Z-α,β,γ,δ-不饱和酰胺类。 次年，Steinhardt 又实现 Zincke 醛热重排-分子内 Diels-Alder 串联反应，成功构建产物中的多环内酰胺骨架。 2008年，Vanderwal 等又报道了利用 Zincke 醛与三丁基锡负离子作用、并用乙酰氯终止反应以合成4-锡基二烯醛类的反应。 这个反应的产物可用作 Stille 反应合成新颖多烯结构的原料。 2009年，Vanderwal 等 （页面存档备份，存于互联网档案馆）报道了由色胺衍生出的 Zincke 醛，在以强碱处理时重排为环合的反应(表环加成)。此反应被用于 norfluorocurarine 的全合成中。 (zh)
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- Zincke aldehydes, or 5-aminopenta-2,4-dienals, are the product of the reaction of a pyridinium salt with two equivalents of any secondary amine, followed by basic hydrolysis. Using secondary amines (as opposed to primary amines) the Zincke reaction takes on a different shape forming Zincke aldehydes in which the pyridine ring is ring-opened with the terminal iminium group hydrolyzed to an aldehyde. The use of the dinitrophenyl group for pyridine activation was first reported by Theodor Zincke. The use of cyanogen bromide for pyridine activation was independently reported by W. König: (en)
- Zincke醛（Zincke aldehydes）即5-氨基-2,4-戊二烯醛类，属于供体-受体双烯类（donor-acceptor dienes），是与两分子仲胺发生作用然后水解得到的产物。此反应与 Zincke 反应类似，不过仲胺的使用令吡啶发生开环，而且端位的亚胺离子基团被水解为醛，最终得到非环取代氨基烯醛。 使用二硝基苯基以活化吡啶环的技术最早是由 Theodor Zincke 报道的。 以溴化氰活化吡啶环的方法则是由 W. König 分别报道。 相关综述： Zincke 反应的一个变体最近（Vanderwal 2006）被用于新颖吲哚衍生物的合成。其中以溴化氰作为吡啶环的活化试剂。 2008年，Steinhardt 等在试图作时，偶然发现 Zincke 醛可在加热的条件下，以较高的立体选择性重排为相应的 Z-α,β,γ,δ-不饱和酰胺类。 次年，Steinhardt 又实现 Zincke 醛热重排-分子内 Diels-Alder 串联反应，成功构建产物中的多环内酰胺骨架。 2008年，Vanderwal 等又报道了利用 Zincke 醛与三丁基锡负离子作用、并用乙酰氯终止反应以合成4-锡基二烯醛类的反应。 这个反应的产物可用作 Stille 反应合成新颖多烯结构的原料。 (zh)
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- Zincke aldehyde (en)
- Zincke醛 (zh)
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