MAOS of Quinoxalines, Conjugated Pyrazolylquinoxalines and Fused Pyrazoloquinoxalines from <scp>l</scp>‐Ascorbic and <scp>d</scp>‐Isoascorbic Acid
作者:El Sayed H. El Ashry、Kamal F. Atta、Salah Aboul‐Ela、Razika Beldi
DOI:10.1080/07328300701252359
日期:2007.3.1
Microwave‐assisted organic synthesis (MAOS) has been used to accelerate the conversion of L‐ascorbic acid (1) and D‐isoascorbic acid (2) to the title heterocycles by conversion to 3‐(L‐threo‐ or D‐erythro‐glycerol‐1‐yl)quinoxaline‐2‐carboxylic acid o‐aminoanilides (7 and 8), which were transformed to lactones 9 and 10, respectively, under acidic condition. The acetylation of compounds 9 and 10 afforded
Isobutylidenation of 1-C-substituted polyols. Attempted extension of the NMR shift rule via the chemical shift difference of their two methyl groups
作者:El Sayed H. El Ashry、Hamida Abdel Hamid、Mahmoud El Habrouk
DOI:10.1016/0008-6215(94)00297-s
日期:1995.2
acetalation as well as the configuration of the polyol. The structure of the products was deduced by a combination of physical and chemical methods. The shift rule for the isopropylidene group has been extended to include the chemical shift difference of the two methyl groups of the isobutylidene rings.
their structure is investigated by 1H, 13C, and 15N NMRspectroscopy. The restricted rotationabout the partial C, N doublebond of the N-acyl derivatives 7–10 is studied by dynamicNMRspectroscopy and the barriers to rotation are determined. In order to assign unequivocally the 15N chemical shifts of N-4 and N-9, in case of 3-substituted flavazoles, exemplary the 1H, 13C, and 15N NMR chemical shifts