| Recently, "green" chemistry, as defined through its 12 Principles by Paul Anastas and John C. Warner in 1998, has gained increased attention - not only in industry, but also in academia. The majority of waste typically generated to build molecular structures is primarily based on organic solvents. One key development in green chemistry focuses on the use of "greener" solvents, or non-traditional media. Another approach eliminates the use of organic solvents, and, therefore, allows reactions to be carried out neat (no solvent) or to use water as the only reaction medium. Due to limited substrate solubility in water, specifically designed surfactants, which upon exposure to water form self-aggregated nanoreactors (micelles), have been shown to host the desired organic transformations. Moreover, based on significantly increased local concentrations of reaction partners, reaction temperatures can be lowered, which, in turn, leads to an improved impurity profile. This concept of micellar catalysis has successfully been explored in Pd-catalyzed allylic silylations of allylic phenyl ethers and Miyaura-type borylations of aryl bromides. Both methodologies provide access to important and synthetically useful building blocks at room temperature in water. Additionally, a second set of designer surfactants with the ability to covalently attach precious metal catalysts has been synthesized. Rh-Catalyzed asymmetric conjugate additions of arylboronic acids to various enones in water, combined with in-flask recycling of the catalyst, have been realized.;Copper-hydride, as one of the oldest properly characterized metal hydrides, has demonstrated its remarkable role in the reduction of various substrate classes. In particular, if exposed to Michael acceptors, the strong tendency of copper complexes to coordinate to the double bond usually leads to overall conjugate reduction. Fortunately, this tendency can be altered and asymmetric ligated copper-hydride has been shown to unexpectedly reduce enones through an alternative route to provide chiral allylic alcohols---important building blocks in organic synthesis. |
