Quantitative analysis of deuterium using the isotopic effect on quaternary C NMR chemical shifts

Quantitative analysis of specifically deuterated compounds can be achieved by a number of conventional methods, such as mass spectroscopy, or by quantifying the residual ¹H NMR signals compared to signals from internal standards. However, site specific quantification using these methods becomes challenging when dealing with non-specifically or randomly deuterated compounds that are produced by metal catalyzed hydrothermal reactions in D₂O, one of the most convenient deuteration methods. In this study, deuterium-induced NMR isotope shifts of quaternary ¹³C resonances neighboring deuterated sites have been utilized to quantify the degree of isotope labeling of molecular sites in non-specifically deuterated molecules. By probing ¹³C NMR signals while decoupling both proton and deuterium nuclei, it is possible to resolve ¹³C resonances of the different isotopologues based on the isotopic shifts and the degree of deuteration of the carbon atoms. We demonstrate that in different isotopologues, the same quaternary carbon, neighboring partially deuterated carbon atoms, are affected to an equal extent by relaxation. Decoupling both nuclei (¹H, ²H) resolves closely separated quaternary ¹³C signals of the different isotopologues, and allows their accurate integration and quantification under short relaxation delays (D1 = 1 s) and hence fast accumulative spectral acquisition. We have performed a number of approaches to quantify the deuterium content at different specific sites to demonstrate a convenient and generic analysis method for use in randomly deuterated molecules, or in cases of specifically deuterated molecules where back-exchange processes may take place during work up.     

Conversion of methyl ketones and methyl sulfones into α-deutero-α,α-difluoromethyl ketones and α-deutero-α,α-difluoromethyl sulfones in three synthetic steps

Deuterodifluoromethyl ketones and sulfones were assembled in three synthetic steps from methyl ketones and sulfones, respectively. The key synthetic transformation is the deuteration of the difluorocarbanion generated by the release of trifluoroacetate from highly α-fluorinated gem-diols. High levels of deuterium on the “CF₂D” group were routinely observed. This strategy is mild and versatile and it can be applied to both ketones and sulfones without additional concerns of over- or under-fluorination. Additional examples address issues of over-deuteration when compounds with other acidic protons are subjected to the reaction conditions. This process not only demonstrates a new method to install a “CF₂D” group but also extends the scope of trifluoroacetate release to sulfones.     

Recent advances in the electrochemical hydrogenation of unsaturated hydrocarbons

Electrochemical hydrogenation of unsaturated organic compounds is emerging as a very promising alternative to the conventional transition-metal-catalyzed transformation as it avoids the preparation, transportation, and storage of pressured molecule hydrogen (H₂). Besides the direct usage of the on-site-generated H₂ on the cathode surface, the electrochemical means also provide opportunities for novel hydrogenation reactions of unsaturated hydrocarbons, especially electrochemical Birch reduction. Another attractive aspect of such an approach is the possibility of highly selective deuteration of unsaturated hydrocarbons with the readily available, cost-effective deuterium source, D₂O.     

芳胺基硫脲类化合物的红外光谱研究

利用烃基异硫氰酸酯分别与邻肼基苯甲酸，５－溴邻肼基苯甲酸，３，５－二溴邻肼基苯甲酸的加成反应，合成了１１种未见文献报道的芳胺基硫脲烃化合物，通过对这些化合物的红外光谱的分析和比较，归属了它们的主要红外吸收峰，考察了主要吸收峰随取代基变化规律。     

Synthesis of Deuterated and Protiated Triacylglycerides by Using 1,1’-Carbonyldiimidazole Activated Fatty Acids

Synthetic model triacylglyceride oils are important compounds for applications in pharmaceutical and food chemistry. Herein, a practical and highly efficient methodology for the synthesis of saturated and unsaturated triacylglycerides utilizing saturated and unsaturated fatty acids activated by 1,1’-carbonyldiimidazole (CDI) has been developed and applied in the synthesis of deuterated medium chain triglyceride (MCT) oil for studies of plant-based and diary food emulsions. The deuterium labelled compounds were used to gain new insight into the mechanism of the reaction, which was confirmed by density-functional theory (DFT) calculations.     

嵌段聚酯型聚脲氨酯弹性体的红外光谱研究

用红外光谱法对基于4,4′－二苯基甲烷二异氰酸酯（MDI）、乙二胺（ED）和聚己二酸丁二醇酯（PBA）（分子量分别为1975和1228）的嵌段聚脲氨酸（PUU）弹性体进行了研究。首先归属了PUU的红外吸收谱带,并对前人已经归属过的1600、1317、1520和1230cm^-1谱带提出了新的看法。氚化和变温技术的使用为上述红外谱带的归属和氢键化研究提供了可靠的理论依据。研究结果表明氢键化主要发生在硬段聚集区中,少量的氢键在软、硬段之间的界面上形成,由此推断PUU材料是相分离的。     

氘化聚酯型聚脲氨酯弹性体的红外光谱研究

用红外光谱法对基于4,4′－二苯基甲烷二异氰酸酯（MDI）、乙二胺（ED）和聚己二酸丁二醇酯（PBA）的嵌段聚酯型聚脲氨酯（PUU）弹性体及其氚化产物进行了研究。结果表明氚化反应对PUU中涉及PUU中涉及氢键化N－H振动红外吸收光谱带的影响较大,受氚化影响较大的那些谱带分别在3332,3190,1600,1539,1317,1257和1230cm^-1附近。另外也发现不同硬段含量和不同聚酯软段分子量的PUU受氚化影响的程度基本相似。     

Chemoselective 1,2-Reduction and Regiodivergent Deuteration of Chromium-Bound Arenes

Herein, a general strategy for chemo- and regioselective 1,2-reduction of chromium-bound arenes was developed, thus providing rapid access to 1,3-cyclohexadienes. Selective arene activation via π-complexation along with the use of mild hydride Ph₃SiH can overcome the inherently low reactivity of arene π-bonds while tolerating various reduction-sensitive functional groups. Its versatility further enables a regiodivergent deuteration. Using different sequences of (non)deuterated hydride and acid reagents, the deuterated positions as well as the degrees of deuterium incorporation can be controlled precisely, which leads to a large and previously inaccessible chemical space for 1,3-cyclohexadiene isotopologues. A reasonable mechanism was proposed based on intermediate capture and control experiments. The synthetic value of this selective 1,2-reduction was demonstrated in the formal total synthesis of (±)-galanthamine and (±)-lycoramine.     

eHydrogenation: Hydrogen-free Electrochemical Hydrogenation

Hydrogenation reactions are staple transformations commonly used across scientific fields to synthesise pharmaceuticals, natural products, and various functional materials. However, the vast majority of these reactions require the use of a toxic and costly catalyst leading to unpractical, hazardous and often functionally limited conditions. Herein, we report a new, general, practical, efficient, mild and high-yielding hydrogen-free electrochemical method for the reduction of alkene, alkyne, nitro and azido groups. Finally, this method has been applied to deuterium labelling.