Synthesis of trans-3,4-dihydroxy-3,4-dihydrophenanthro[3,2-b ][1]benzothiophene, a potentially carcinogenic metabolite of sulfur heterocycle phenanthro[3,2-b ][1]benzothiophene
作者:Subodh Kumar
DOI:10.1039/b100345n
日期:——
The present study describes the synthesis of trans-3,4-dihydroxy-3,4-dihydrophenanthro[3,2-b][1]benzothiophene (3), which is a potential proximate carcinogen of the environmentally occurring potent carcinogen phenanthro[3,2-b][1]benzothiophene (1). Three approaches were investigated for the synthesis of 3. In the first approach, the diarylalkene 9, which was prepared by the Wittig reaction of ylide 7 and aldehyde 8, was subjected to an oxidative photocyclization reaction to produce a mixture of compounds from which 5, a synthetic precursor to 3, was obtained only in trace amounts. The major cyclized product was 10. The second approach entailed the Suzuki cross-coupling reaction of 2-(dihydroxyboryl)-5-methoxybenzaldehyde (12) with 3-bromodibenzothiophene (11) to produce 13 in 92% yield. The aldehyde function of 13 was elongated with trimethylsulfonium iodide in the presence of KOH to generate the ethylene oxide 14, which, after methanesulfonic acid treatment, produced a 1 ∶ 1 mixture of 3-methoxyphenanthro[3,2-b][1]benzothiophene (6) and 3-methoxyphenanthro[1,2-b][1]benzothiophene (15). Only the undesired compound 15 could be isolated in pure form by extracting the mixture with hot ethanol,
leaving behind a 7 ∶ 3 mixture of 6 and 15. In the third approach, the Wittig reaction of 7 with 2-bromo-5-methoxybenzaldehyde (16) produced 17 predominantly as the Z-isomer in quantitative yield. Cyclodehydrobromination of 17 with KOH–quinoline at elevated temperature produced a mixture from which 6 and 3-methoxyphenanthro[3,4-b][1]benzothiophene (18) were easily separated by column chromatography in 23 and 51% yields, respectively. The intermediate 6 was conveniently processed to 3 following the reaction sequence: methoxy phenol→o-quinone→dihydrodiol.
A relatively polar dihydrodiol obtained by similar processing of the mixture of 6 and 15 was identified as 3.
本研究描述了反式-3,4-二羟基-3,4-二氢菲并[3,2-b][1]苯并噻吩(3)的合成,这是一种环境中的强致癌物菲并[3,2-b][1]苯并噻吩(1)的潜在前致癌物。我们研究了三种合成3的方法。在第一种方法中,通过Wittig反应制备的二芳基烯烃9与醛7反应,经过氧化光环化反应生成一组化合物,其中合成3的前体5仅以微量形式存在。主要的环化产物是10。第二种方法涉及Suzuki交叉偶联反应,将2-(二羟基硼基)-5-甲氧基苯甲醛(12)与3-溴二苯并噻吩(11)反应,以92%的收率生成13。13的醛基在KOH存在下通过三甲基硫鎓碘延长,生成环氧乙烷14,经过甲磺酸处理后,生成3-甲氧基菲并[3,2-b][1]苯并噻吩(6)和3-甲氧基菲并[1,2-b][1]苯并噻吩(15)的1:1混合物。只有不希望的15能够在用热乙醇提取混合物后以纯形式分离出来,留下7:3的6和15混合物。在第三种方法中,7与2-溴-5-甲氧基苯甲醛(16)经过Wittig反应主要生成Z-异构体17,其收率是定量的。17在高温下通过KOH-喹啉进行环脱溴反应,生成一组混合物,其中6和3-甲氧基菲并[3,4-b][1]苯并噻吩(18)能够通过柱层析分别以23%和51%的收率轻易分离。中间体6通过甲氧基酚→邻醌→二氢二醇的反应序列方便地转化为3。通过类似的处理方法获得的相对极性的二氢二醇确定了为3。