A safe, convenient, and regioselective synthesis of 3-halo coumarins using a metal halide (CuX2 alone or with ZnX2) promoted halogenation with N-halosuccinimide (NXS) as halide source is reported. The synthesis involved the steady in situ generation of highly reactive positive halogen (X+) by the coordination of copper or zinc with the N-halosuccinimide and subsequent electrophilic aromatic substitution
Benzopyrans. Part 41. Reactions of 2-(2-dimethylaminovinyl)-1-benzopyran-4-ones with various dienophiles
作者:Chandra Kanta Ghosh、Samita Bhattacharyya、Chandreyi Ghosh、Amarendra Patra
DOI:10.1039/a903145f
日期:——
propiolate (EP) ultimately gives xanthenones 33, 34 and 37, respectively, the latter being admixed with flavone 43. Enamine 2, cyclisable to xanthenone 11, gives 33 and 35 with DMAD, and 37 and 44 with EP. Reaction of 3 with DMAD affords 36 exclusively.
Ti/Zn-mediated McMurry coupling of a series of 4-oxo-4H-chromene-2-carbaldehydes afforded unusual chemoselective CH2–CH2 tethered bis-chromones. Studying the reaction parameters and reagents further confirmed that the formation of unexpected coupled products is selective to 4-oxo-4H-chromene-2-carbaldehydes. This methodology demonstrated a simple and efficient route for the synthesis of bis-chromones
Ti / Zn介导的一系列4-oxo-4 H -chromene-2-carbaldehydes的McMurry偶联提供了不同寻常的化学选择性CH 2 -CH 2系双色酮。对反应参数和试剂的研究进一步证实,出乎意料的偶联产物的形成对4-氧代-4 H-亚甲基-2-甲醛具有选择性。该方法论证明了合成双色酮的简单有效途径。
Visible light-enabled regioselective chlorination of coumarins using CuCl<sub>2</sub><i>via</i> LMCT excitation
efficient, regioselectivechlorination of coumarins using Earth-abundant and cost-effective CuCl2 under visible light irradiation is reported. A key feature of this protocol is the photocatalytic dissociation of the copper(II) complex in acetonitrile through ligand-to-metal charge transfer (LMCT) to give the chlorine atom which then selectively chlorinates the coumarin. This method can chlorinate a broad
报道了在可见光照射下使用地球丰富且具有成本效益的 CuCl 2对香豆素进行有效的区域选择性氯化。该协议的一个关键特征是通过配体到金属电荷转移 (LMCT) 将乙腈中的铜 ( II ) 配合物光催化解离,从而产生氯原子,然后选择性地氯化香豆素。该方法可以用吸电子或给电子取代基对范围广泛的香豆素进行氯化,以区域选择性地提供 3-氯香豆素,并以良好至优异的产率进一步扩展到其他缺电子杂环和烯烃,例如黄酮、8-甲氧基补骨脂素和萘醌。
Dike, Suneel Y.; Mahalingam, Murli, Synthetic Communications, 1989, vol. 19, # 20, p. 3443 - 3452