C3‐Functionalized Chromones Synthesis by Tandem C−H Elaboration and Chromone Annulation of Enaminones

Abstract

Chromone is a heterocyclic entity presents in a number of natural products, clinical pharmaceuticals, as well as molecules with enriched biological functions. As cuttingedge area, the synthesis of chromones has seen spectacular progress over the past decade. Among the available synthetic modes toward chromone scaffolds, the annulation of orthohydroxyphenyl functionalized N,N-disubstituted enaminones has turned out to be one of the most reliable and practical ones. By combining this annulation with the featured transformation of the vinyl α-CÀ H bond in the enaminone structure, a large number of tandem reactions providing structurally diverse chromones with C3-functionalization have been recently realized. As a practical strategy in the synthesis of valuable heterocyclic molecules and an important branch in the enaminone-based organic synthesis, such synthetic reactions are highly instructive for organic chemistry and many other disciplines related to this heterocyclic moiety. Herein, we present for the first time the research advances on the synthesis of C3-functionalized chromones via tandem vinyl CÀ H bond elaboration and chromone annulation of ortho-hydroxyphenyl functionalized tertiary enaminones. 2 3 4 5 6 7 8

Transition Metal‐free C−H Sulfonylation and Pyrazole Annulation Cascade for the Synthesis of 4‐Sulfonyl Pyrazoles

“…[15] However, the reaction has been found unpractical when N,N-disubstituted tertiary enaminone is employed to the reported catalytic method using water as medium. While tertiary enaminones have been previously disclosed with highly enriched transformation pathways in different organic reactions, [16] it is desirable that such enaminones may also be used for the synthesis of 3-unsubstituted 4sulfonyl pyrazoles by using these typical N,N-dimethyl enaminones as substrates. Herein, we report the practical domino reactions of N,N-dimethyl enaminones and sulfonyl hydrazines featured with domino metal-free CÀ H elaboration [17] and pyrazole annulation for the synthesis of 4-sulfonyl pyrazoles without substituent in the C3 site.…”

Recent Advances in Organic Synthesis Based on N,N-Dimethyl Enaminones

“…In the first half of 2019, Wan and Fu reviewed the research advances made on the synthesis of 3-substituted chromones by cascade reactions involving C-H bond elaboration of 2-hydroxyphenyl enaminones and chromone cyclization. 63 Therefore, in this section, we exclude those reports on the synthesis of 3-substituted chromones that were reviewed by Wan and Fu. Almost simultaneously in 2019, the groups of Behera, 64a Yang 64b and ours 64c independently developed methods for the synthesis of 3-fluorochromones from o-hydroxy-arylenaminones by using Selectfluor as the fluorine source (Scheme 60). 64 In Yang's method, 64b the enaminone was initially fluorinated by Selectfluor to form an iminium ion, followed by tautomerization to give an enamine.…”

Synthesis of 6,7-Dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles by Azomethine Imine-Alkyne Cycloadditions Using Immobilized Cu(II)-Catalysts

“…Acid-catalyzed reactions with N -, C -, and O -nucleophiles take place under mild conditions by substitution of the dimethylamino group to give β-functionalized propenoates. With ambident nucleophiles, enaminones undergo cyclization into different heterocyclic systems [ 28 , 29 , 30 , 31 , 32 , 33 ]. Enaminones are also used as alkenes in cycloaddition reactions [ 34 , 35 , 36 , 37 , 38 ] and as bidentate N, O ligands [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ] and tetradentate acacen-type ligands [ 27 , 50 , 51 , 52 , 53 , 54 ] to coordinate metal ions.…”