Radical chlorination of bicyclo[1.1.1]pentane-1,3-dicarboxylic acid is highly selective, and up to four chlorine atoms can be introduced relatively easily without damage to the strained bicyclic cage. Combined with hydrodechlorination with TMS₃SiH, direct chlorination provides access to five of the 15 possible chlorinated diacids. Their configuration has been established by X-ray diffraction. Their pK_a values have been measured by capillary electrophoresis and calculated at the B3LYP-D3BJ/6-311+G(d,p)-level. The results are in good agreement and reflect the expected trend, from 2.78 ± 0.08 and 4.14 ± 0.10 in the parent to 1.07 ± 0.03 and 2.31 ± 0.03 in the tetrachlorinated diacid. Strain energy relative to the parent diacid was calculated for all 15 chlorinated diacids and shows a dramatic increase with successive chlorination, due to nonbonded Cl–Cl repulsions.

中文翻译：

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桥氯化双环[1.1.1]戊烷-1,3-二羧酸

双环[1.1.1]戊烷-1,3-二羧酸的自由基氯化反应具有很高的选择性，可以相对容易地引入多达四个氯原子，而不会损坏应变的双环笼。与TMS ₃ SiH加氢脱氯相结合，直接氯化可提供15种可能的氯化二酸中的5种。通过X射线衍射已经确定了它们的构型。他们的p K _a通过毛细管电泳测量值，并以B3LYP-D3BJ / 6-311 + G（d，p）水平计算。结果吻合良好，反映了预期的趋势，从母体的2.78±0.08和4.14±0.10到四氯二酸的1.07±0.03和2.31±0.03。计算了所有15种氯化二酸相对于母体二酸的应变能，并且由于未键合的Cl-Cl排斥作用，其随连续氯化反应而显着增加。