Elektrohemijsko bromovanje estrogena i zaštićenig glikala
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U ovom radu ispitane su mogućnosti primene elektrohemijskog generisanja halogena u organskoj sintezi. Kako se elementarnim halogenima organska jedinjenja mogu halogenovati na dva načina – elektrofilnim supstitucijama (aromati) i adicijama (nezasićena jedinjenja) – kao supstrati su odabrani estron (1) i estradiol (2)(za izučavanje prve reakcije) i peracetilovani glikali: 3,4,6-tri-O-acetil-D-glukal(9), 3,4,6-tri-O-acetil-D-galaktal (10) i 3,4-di-O-acetil-6-deoksi-L-glukal (11) (za izučavanje druge reakcije).
In this work the possibilities of the application of an electrochemical generation of halogens in organic synthesis were investigated. Since organic compounds can be halogenated by free halogens in two ways – by electrophilic substitutions (aromatics) and additions (unsaturated compounds) – estrone (1) and estradiol (2), as well as peracetylated glycals 3,4,6-tri-O-acetyl-D-glucal (9), 3,4,6-tri-O-acetyl-D-galactal (10) and 3,4-di-O-acetyl-6-deoxy-L-glucal (11), were chosen as the substrate in order to study both reaction types. The monobromination of the A-rings of estrone and estradiol has been successfully achieved by simple constant current electrolysis of these compounds and tetraethylammonium bromide in acetic acid, dichloromethane and dimethylsulfoxide as the solvents. With the 2 Fmol−1 charge consumption electrolysis both estrogens gave two regioisomers (2- and 4-bromoestrone (4a and 4b), i.e. 2- and 4-bromoestradiol (6a and 6b))in all three solvents. The ratio of the regioisom...eric bromides obtained in acetic acid and dichloromethane was 1:1.09 - 1:1.50, and the addition of water or acetanhydride to acetic acid did not affect this ratio. The bromination of estrogens by conventional methods described in the literature, that were also been conducted in the course of this study (for comparison of purposes), gave the same result and the presence of bromides during the brominations did not influence the ratio of the two regioisomers. However, both the chemical and electrochemical brominations in dimethyl sulfoxide resulted in the same product 1:2,5 -2,6. The overall yield of the both regioisomers electrochemical monobromination was very high (up to 97%).
Faculty:University of Kragujevac, Faculty of Science
- Novel Electrochemical and Chemical Methods in Synthesis of Organic Compounds of Interest for Medicine and Material Chemistry (RS-172034)