Facile Synthesis of Regioisomeric N‐Alkyl Substituted 3‐Methylene‐3,4‐dihydroquinoxalin‐2(1H)‐ones

Abstract

Facile and convenient synthetic approaches towards pharmaceutically important regioisomeric N‐alkyl substituted 3‐methylene‐3,4‐dihydroquinoxalin‐2(1H)‐ones have been developed. Various approaches to the target compounds were tested and compared. Products having bulky N4‐propyl substituent were found to exist in two forms in solutions due to solvent‐dependent rotational processes in 2‐oxoethylidene moiety, which is of interest for construction of optical, electronic, and other functional materials. The proposed procedures proceed in a highly regioselective manner under mild conditions, and the products are isolated without usage of column chromatography.

Synthesis of 1,4-benzothiazinones from acylpyruvic acids or furan-2,3-diones and o-aminothiophenol

“…To develop an approach to target the BTAs III, we analyzed the general synthetic methods to enaminones I and II, which involve the reaction of the acylpyruvic acids or their esters IV, 5-arylfuran-2,3-diones V, and acetylenedicarboxylates VI with o-aminophenols or o-phenylenediamines (Scheme 3) [1][2][3][4][5][6].…”

“…Product 3a was formed when the o-aminothiophenol's SH group attacked the compound 5a at the lactone carbonyl group, and the product 4a, when o-aminothiophenol's NH 2 group attacked compound 5a at the lactone carbonyl group. The in situ formation of 5-phenylfuran-2,3-dione (5a) was indicated by the appearance of bright yellow color (characteristic for the 5-arylfuran-2,3-diones 5 [6]) after mixing the suspension of acid 2a with a carbodiimide. In addition, after mixing the suspension of acid 2a in acetonitrile with DIC, the formation of the yellow precipitate of 5-phenylfuran-2,3-dione (5a) was observed, and compound 5a could be isolated by simple filtration.…”

“…Enaminones fused to the 1,4-benzoxazine-2-one I or quinoxaline-2(1H)-one II moiety ( Figure 1) represent an intensively investigated class of enamines. Undying interest in these compounds is due to the simplicity of their synthesis and purification, the availability of starting materials and the possibility of their synthesis under mild green conditions [1][2][3][4][5][6]. Because of their availability in gram-scale quantities, these compounds were thoroughly investigated for the possibility of practical use.…”

2-Imidazolidinone benzofurans as unexpected outcome of the Lewis acid mediated Nenitzescu reaction

“…Herein we report the Lewis acid mediated regioselective metal-free synthesis of 2-imidazolidinone benzofurans from easily accessible piperazinone enaminoesters 5a-i. [41][42][43] It was hypothesized that changing the solvent of the reaction of BQ 1a and 5a to trifluoroacetic acid (TFA), with reduced nucleophilicity compared to AcOH, would lead to the unsubstituted 5-hydroxyindole 6. Surprisingly, compound 7a was obtained in 46% yield, which structure was verified by X-ray diffraction (XRD) (Table 1, entry 1, XRD: Fig.…”