Intermolecular C–H Amination of Complex Molecules: Insights into the Factors Governing the Selectivity

Transition-metal-catalyzed C–H amination via nitrene insertion allows the direct transformation of a C–H into a C–N bond. Given the ubiquity of C–H bonds in organic compounds, such a process raises the problem of regio- and chemoselectivity, a challenging goal even more difficult to tackle as the complexity of the substrate increases. Whereas excellent regiocontrol can be achieved by the use of an appropriate tether securing intramolecular addition of the nitrene, the intermolecular C–H amination remains much less predictable. This study aims at addressing this issue by capitalizing on an efficient stereoselective nitrene transfer involving the combination of a chiral aminating agent <b>1</b> with a chiral rhodium catalyst <b>2</b>. Allylic C–H amination of terpenes and enol ethers occurs with excellent yields as well as with high regio-, chemo-, and diastereoselectivity as a result of the combination of steric and electronic factors. Conjugation of allylic C–H bonds with the π-bond would explain the chemoselectivity observed for cyclic substrates. Alkanes used in stoichiometric amounts are also efficiently functionalized with a net preference for tertiary equatorial C–H bonds. The selectivity, in this case, can be rationalized by steric and hyperconjugative effects. This study, therefore, provides useful information to better predict the site of C–H amination of complex molecules

Improvement of Water Resistance of Hemp Woody Substrates through Deposition of Functionalized Silica Hydrophobic Coating, While Retaining Excellent Moisture Buffering Properties

This paper reports on the development of a novel treatment for hemp shiv that improves resistance to liquid water and protects hemp shiv from biodegradation without impacting the natural ability of the shiv to buffer moisture vapor. The hydrophobic surface was produced by depositing silica nanoparticles, which were prepared by the functionalization of silica nanoparticles with hexamethyldisilazane (HMDS). The surface chemical composition was determined showing replacement of surface silanols on the silica nanoparticles with trimethyl groups. The specific surface area of silica nanoparticles decreased after the trimethylsilyl treatment. The surface modifications reduced the level of hysteresis between absorption and desorption isotherms and also the total amount of moisture absorbed by the silica nanoparticles. The surface of the hemp shiv was initially hydrophilic but became hydrophobic once the material was treated, demonstrating contact angle with water of 120°. The results show the coating layer of functionalized silica on the hemp shiv reduced water absorption from 400% (untreated shiv) to 250%. However, the moisture buffer value results showed that the coating films do not limit the access of moisture to adjacent pores in the hemp shiv, and the functionalized silica coating layer retains the moisture buffering ability of hemp shiv