Synthesis
The general procedure for the synthesis of 6-nitro-3,4-dihydrochromanone from 3-(4-nitrophenoxy)propionic acid is as follows: 3-(4-nitrophenoxy)propionic acid (6.5 g, 30 mmol), concentrated sulfuric acid (30 mL), and phosphorus pentoxide (5.2 g, 37 mmol) were mixed, and the reaction was stirred for 3 hours at 60 °C. After the reaction was completed, the mixture was poured into ice and stirring was continued for 15 minutes. Subsequently, extraction was carried out with ethyl acetate and the organic phase was washed with saturated aqueous sodium bicarbonate and dried over anhydrous magnesium sulfate. Finally, the organic phase was concentrated in vacuum to afford 6-nitro-3,4-dihydrochromanone as a beige solid (5.5 g, 94% yield) with a melting point of 171-173 °C. The structure of the product was confirmed by NMR and mass spectrometry.
References
[1] Patent: WO2005/37830, 2005, A1. Location in patent: Page/Page column 18
[2] Patent: EP2487171, 2012, A1. Location in patent: Page/Page column 9
[3] Patent: WO2014/418, 2014, A1. Location in patent: Page/Page column 97
[4] Patent: US2015/197511, 2015, A1. Location in patent: Paragraph 0450; 0451
[5] Patent: CN108440404, 2018, A. Location in patent: Paragraph 0075; 0079; 0080; 0081
