“…9 Its chemical resolution was carried out with (ϩ)-(1-phenylethyloxamoyl)hydrazine 7, a carbonyl derivatizing agent 10-13 (Scheme 1). In contrast to previous findings, [10][11][12][13] where the resolution of chiral ketone derivatives with 7 resulted in the two corresponding diastereomers, which could be separated by fractional crystallization, the condensation of rac-6 with this reagent, monitored by TLC, showed the formation of four products of comparable ratio instead of two. The 1 H NMR spectrum of the crude product clearly indicated that the syn Z-and anti E-isomers of both diastereomers [(Z )-(ϩ)-8/(E )-(ϩ)-8, (Z )-(Ϫ)-8/(E )-(Ϫ) -8] were present in this mixture (Scheme 1).…”
“…9 Its chemical resolution was carried out with (ϩ)-(1-phenylethyloxamoyl)hydrazine 7, a carbonyl derivatizing agent 10-13 (Scheme 1). In contrast to previous findings, [10][11][12][13] where the resolution of chiral ketone derivatives with 7 resulted in the two corresponding diastereomers, which could be separated by fractional crystallization, the condensation of rac-6 with this reagent, monitored by TLC, showed the formation of four products of comparable ratio instead of two. The 1 H NMR spectrum of the crude product clearly indicated that the syn Z-and anti E-isomers of both diastereomers [(Z )-(ϩ)-8/(E )-(ϩ)-8, (Z )-(Ϫ)-8/(E )-(Ϫ) -8] were present in this mixture (Scheme 1).…”
“…To determine the absolute configuration of these 1,4-adducts, the benzyloxycarbonyl group of 2a (98% ee; Table , entry 3) was removed under basic aqueous conditions, obtaining known compound 3 in 82% yield with no erosion of ee (98% ee; eq 2). By comparison of the optical rotation with the literature value, the absolute configuration was determined to be ( R ). …”
[reaction: see text] The first catalytic asymmetric synthesis of 2-aryl-2,3-dihydro-4-quinolones has been developed by way of a rhodium-catalyzed 1,4-addition of arylzinc reagents to 4-quinolones. These 1,4-adducts can be obtained with high enantioselectivity by the use of (R)-binap as a ligand, and high yields are realized by conducting the reactions in the presence of chlorotrimethylsilane.
“…However, only a few methods have been reported for the preparation of 2,3‐dihydroquinolone, limiting the prospects for extensive study of these compounds. Typically, corrosive reagents like orthophosphoric acid, acetic acid, or strong alkalis have been used for catalyzing the isomerization of substituted 2‐aminochalcones to 2,3‐dihydroquinolones, which possibly limits the substrate scope considerably (Scheme a) –. Recently, intramolecular cyclization under milder conditions using transition‐metal catalysts or organocatalysts have emerged as important strategies.…”
In this study, a series of variously substituted 2,3-dihydroquinolin-4-imines (DQIs) were synthesized from N-substituted propargylanilines by copper(I)-catalyzed annulation. The approach adopted in this study under mild, effective conditions exhibited broad substrate tolerance, particularly for functional groups substituted on anilines. Most of the DQI derivatives synthesized under optimal conditions were obtained in good isolated yields of 63-88 %. 2,3-Dihydroquinolinimine thus obtained was easily converted to important structures like 2,3-dihydroquinolone and tetrahydrobenzodiazepin-5-one, confirming the importance of this strategy in constructing various heterocycles. Surprisingly, 2,3-dihydroquinolinimines thus obtained exhibited bright fluorescence with quantum yields up to 66 %. The density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed for understanding the excited-state nature of DQI system. Accordingly, a tailored DQI derivative bearing methoxy group at C-6 position and acetoxy group at C-7 position was designed and synthesized to give emission at 559 nm with redshift compared to the 7-methoxy substituted DQI. A detailed study of DQI structures with their photophysical properties was performed with five control molecules and consequently demonstrated the uniqueness of the chemical structures of DQIs.
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