The dehydrogenation of cholesterol, Î3,5 -cholestadiene, and related unsaturated compounds to afford aromatic hydrocarbons with the skeleton of 17H-cyclopenta-[a]-phenanthrene may be effected by reaction with quinones possessing high redox potentials, e.g., tetrachloro -p-benzoquinone (chloranil), 2,3 -dichloro-5,6-dicyanobenzoquinone (DDQ), etc., in high-boiling solvents such as p-xylene and anisole at reflux temperature. The reaction proceeds stepwise. Angular methyl groups present in the steroid molecule either migrate to the 1,4, or 17 positions, or are eliminated. This dehydrogenation reaction may also be applied to seco-steroids such as vitamin D. With suitable steroids, Diels-Alder additon of the quinone to partially dehydrogenated intermediates possessing a cis-1,3-diene group is the predominant reaction; the addition products are further dehydrogenated to polycyclic aromatic compounds. In the case of some estrone derivatives and related compounds, the dehydrogenation reaction involves opening of ring D. The reaction may serve to prepare certain aromatic compounds, the synthesis of which is difficult by other methods.
胆固醇、3,5-胆甾二烯和相关的不饱和化合物脱氢,生成骨架为17H-环戊并[a]
菲的
芳香烃,可通过与具有高氧化还原电位的
醌类(如四
氯对苯醌(
氯醌)、2,3-二
氯-5,6-二
氰基苯醌(
DDQ)等)在回流温度下在四氢苯和
苯甲醚等高沸点溶剂中反应来实现。反应是逐步进行的。甾体分子中的甲基角基会移动到1,4或17位,或被消除。这种脱氢反应也可用于
维生素D等次甾体。对于合适的甾体,
醌类与部分脱氢中间体(具有顺式-1,3-二烯基)的Diels-Alder加成反应是主要反应;加成产物进一步脱氢生成多环
芳烃。对于某些
雌酮衍
生物和相关化合物,脱氢反应涉及D环的打开。该反应可用于制备某些芳香族化合物,这些化合物的合成很难通过其他方法实现。