A Novel Aldol Condensation Alternative:α,β-Unsaturated Aldehydes from 3-Hydroxy-1-alkynes via Dihydrodioxepins
摘要:
The controlled aldol condensation between an aliphatic ketone and an acetaldehyde equivalent remains a challenge. One solution to this evergreen problem consists of the nucleophilic addition of acetylene to the ketone and the subsequent isomerization of the resulting 3-hydroxy-1-alkyne to the corresponding 2-alkenal. So far, however, the latter step could only be executed with acid-insensitive substrates. We now present a milder, three-step method which extends the scope of the procedure considerably. In the first step, the 3-hydroxy-1-alkynes are converted into 2-propynyl ethylene glycol monoethers; these then undergo base-catalyzed cyclization to give the dihydro-1,4-dioxepins, which are hydrolyzed in acidic medium in the third and final step.
The first total synthesis of (-)-graminin A is described. Key features of our synthetic approach involve a palladium-catalyzed asymmetric cyclization carbonylation of prochiral propargylic acetate, conversion of the orthoester product into methyl 4-oxo-3-furancarboxylate, and copper complex-mediated aldol condensation of (+)-gregatin B bearing a diene moiety. A new synthesis of (+)-gregatin B and the
Here, we present a new strategy for the totalsynthesis based upon a skipped diyne as central building block. This was transformed so far into an advanced intermediate related to the pharmacophore of the jerangolids.
hydrogenation of numerous structurally diverse alkynes proceeded in moderate to excellent yield under mild conditions. The high selectivity toward the industrially important alkene substrates, functional group tolerance, and the high recyclability makes the catalytic system unique. Both high activity and selectivity are correlated with a frustratedLewispairs interface formed by the combination of gold
1,10-菲咯啉在TiO 2上热解Au(OAc)3提供了一种高活性和选择性的Au纳米颗粒(NP)催化剂,该催化剂嵌入氮掺杂的碳载体中,[受电子邮件保护]碳/ TiO 2催化剂。系统研究了热解温度,载体类型和氮配体以及Au /配体摩尔比等参数。在温和条件下,许多结构多样的炔烃的高选择性加氢以中等至极好的收率进行。对工业上重要的烯烃底物的高选择性,官能团耐受性和高可回收性使催化体系独树一帜。高活性和选择性都与由N掺杂碳的金和氮原子的组合形成的沮丧的Lewis对界面有关,根据密度泛函理论计算,该界面可以充当促进H 2杂化活化的基本位点在非常温和的条件下。这种“完全非均相”且可循环利用的金催化剂使选择性加氢工艺在环境和经济上都具有吸引力。
Synthesis and Rearrangement of 3-Methyl-1,4-pentadiyne-3-ol
An efficient synthesis and rearrangement of 3-methyl-1,4-pentadiyne-3-ol (1) using perrhenate- and Mo(VI)-catalysts is reported. The by-products 3,6-dimethyl-1,4,7-octatriyne-3,6-diol (2) and 3-ethynyl-5-methyl-1,6-heptadiyne-3,5-diol (3) were isolated and spectroscopically characterized. A possible reaction mechanism for the formation of the byproducts is discussed.