4H-Chromenes were synthesized from 2-bromobenzylidenemalonates and 1,3-dicarbonyls undermild and simple reaction conditions via copper-catalysed domino reactions involving Michael addition and intramolecular Ullmann-type C(aryl)–O bondformation. Although a competitive elimination affected these reactions, this catalytic system readily provided chromenes with functionality at the C-4 position.
Catalyst-free transfer hydrogenation of activated alkenes exploiting isopropanol as the sole and traceless reductant
作者:Tamal Kanti Das、Agustin M. Rodriguez Treviño、Sanjay Pandiri、Sini Irvankoski、Juha H. Siitonen、Sara M. Rodriguez、Muhammed Yousufuddin、László Kürti
DOI:10.1039/d2gc04315g
日期:——
Both metal-catalyzed and organocatalytic transfer hydrogenation reactions are widely employed for the reduction of CO and CN bonds. However, selectivetransfer hydrogenation reactions of CC bonds remain challenging. Therefore, the chemoselective transfer hydrogenation of olefins under mild conditions and in the absence of metal catalysts, using readily available and inexpensive reducing agents (i.e
金属催化和有机催化转移加氢反应都广泛用于还原 C O 和 C N 键。然而,C C 键的选择性转移氢化反应仍然具有挑战性。因此,在温和条件下和在没有金属催化剂的情况下,使用容易获得且廉价的还原剂(即伯醇和仲醇)对烯烃进行化学选择性转移加氢,将标志着绿色转移加氢策略的发展取得了重大进展。本文描述的是活性烯烃的非常规无催化剂转移氢化反应,使用异丙醇作为环保还原剂和溶剂。该反应以中等至良好的收率方便地合成了多种取代的丙二酸半氧酯 (SMAHO)。机理研究指出了一种前所未有的氢键辅助转移氢化过程。
Alkylidene Meldrum′s Acid as Acceptor‐Donor‐Acceptor with Azomethine Ylide for Organocatalytic Asymmetric (3+2) Cycloaddition/Annulation: Synthesis of Chromeno[4,3‐<i>b</i>]pyrrolidine
作者:Yan‐Cheng Liou、Yi‐Ru Chen、Ching‐Wen Hsu、Xuan‐Rui Huang、Heng‐Wei Wang、Wenwei Lin
DOI:10.1002/adsc.202300609
日期:2023.11.7
A quinine-derived thiourea-catalyzed enantioselective double annulation strategy using alkylidene Meldrum′sacid as an acceptor-donor-acceptor with salicylaldehyde-derived azomethine ylide is reported. The methodology is realized via a (3+2) cycloaddition/transesterification/decarboxylation sequence, giving chromeno[4,3-b]pyrrolidines within 15–420 minutes at room temperature in 51–97% yields with
A general and practical preparation of alkylidene Meldrum’s acids
作者:Aaron M. Dumas、Adam Seed、Alexander K. Zorzitto、Eric Fillion
DOI:10.1016/j.tetlet.2007.08.012
日期:2007.10
Although many methods have been reported for the Knoevenagel condensation of aldehydes and Meldrum's acid, most are not general or use unconventional reagents and conditions. We have found that alkylidene Meldrum's acids form readily in benzene solution under mild pyrrolidinium acetate catalysis, and that this reaction is general, highly functional group compatible, and can be scaled-up easily. (c) 2007 Elsevier Ltd. All rights reserved.