Lao Wenjian, S. Xuejun, You Jinmao
2000
Citations
0
Influential Citations
2
Citations
Journal
Heterocyclic Communications
Abstract
Introduction Numerous carbazole derivatives exhibit a significant biological activities, such as anticonvulsant. antimicrobial, antiviral, anti inflammatory, and analgesic. Some copolymers containing carbazole chromophores express high excitation energy transport eff ic iency; and their photophysical processes have been the subject of many investigations . A m o n g these carbazole derivatives, carbazole-9-carboxylic acids were important intermediates. Synthetic efforts directed at this class of compounds has been limited. These conventional heating reactions are multi-steps, t ime-consuming and with low ultimate yields. Due to limitations in synthetic methods for these compounds, coupled with our interests in the microwave-assisted reactions , an alternate approach to these compounds was needed. Microwave-assisted treatment of liquid and solid samples has been a very helpful method for organic and inorganic synthesis and its application in rapid synthetic organic chemistry has received much attention in recent years . In this communica t ion , we describes a methodology for preparation some substituted carbazole-9acetic/propionic acid assisted by microwave irradiation. Results and discussion Synthesis of substituted carbazole-9acetic/propionic acid. The starting material. 1,4-dimethyl-carbazole, was prepared according to the reported methods, and obtained in * corresponding author 81 Vol. 6, No. 1, 2000 Microwave-assisted preparation of substituted carbazole-9-acetic/propionic acid and their absorption and fluorescence spectroscopic characteristics satisfactory yields . A mixture of 1.4-diinethyl-carbazoIe with bromo-esters and potassium hydroxide in N.Ndimethylformamide ( DMF ) was irradiated in an open vessel in a domestic microwave oven for 6 minute, and treated with water and hydrochloric acid to afford 1.4-dimethyl-carbazole-9-acetic/propionic acid in 85%/83% yield. The helogented-carbazoles were syntheticed according to the literature ". Similarly, their reaction with bromo-ester was carried out. and the results are summarized in table 1 (Scheme 1) Scheme 1 1a Xi,3=CH3 X2,4=H 2a Xi.3=CH3 X2 ,4=H n=0 1b X 2 = l Xi,3,4=H 2b X i , 3 = C H 3 X 2 , 4 =H n=1 1c X2,4=CI X i , 3 = h 2c X 2 =l Xi ,3 ,4 = h n = 0 1d X2i4=Br Xi,3=H 2 d 2,4=CI Xi , 3 =H n=0 1f Xi,2,4=Br X3=H 2f X2,4 = B r X i , 3 = h n=0 2 e Xi , 2 ,4=Br X 3 = H n=1 Table 1 The microwave-assisted reaction of the substituted carbazole with bromo-ester product Bromo-ester Microwave Irradiation Yield mp/°C a power(w) time (min) (%) 2a BrCH2COOC2H5 375 6 67 165-166 2b BrCH2CH2COOC2H5 375 6 65 175-177 2c BrCH2COOC2H5 375 4 85 162-164 2d BrCH2COOC2H5 375 5 81 224-225 2e BrCH2COOC2H5 375 5 78 245-246 2f BrCH2CH2COOC2H5 375 8 45 185-186 a: 2a, lit 164-166"C. 2c, lit '162-163 °C. 2e, lit243-247 When the vicinal positions of the N-H bond have substituted group, like compound la and le, the irradiated time was resulted in longer under microwave power at 375W so as to give the good yields. To increase the irradiating time under this microwave power gave more tar as well as lower yield. In case of microwave power at 225W. the desired yield would not been obtained owing to more substrate no reacted. Whereas higher microwave power above 525 W leaded to give more tar. The amount of KOH to the yield was also important. The range of mole ratio L. Wenjian et al. Heterocyclic Communications of KOH and substituted carbazole within 3-5 was suitable for the reaction. In contrast to the ' w e t ' reaction, we tried to perform the reaction in absent of solvent, so-called ' d ry ' condit ion, but only little product was obtained. Thus, it is worthy to note that the reactivity of the compounds ( l a l e ) toward microwaveinduced reaction, to a large extent, on the sort of reaction media, the strength of microwave power, the time of irradiation, the position of the substituted group on the mother ring of the carbazole, and the ratio of the starting material. u υ c CO L* c V) -C CO 1