Combinatorial chemistry hydrogenation

Immobilized catalysts on solid supports inherently have benefits because of their easy separation from the products and the possibility of recycling. They are also expected to be useful for combinatorial chemistry and high-throughput experimentation. The polystyrene-bound BINAP/DPEN-Ru complex (beads) in the presence of (CH3)3COK catalyzes the hydrogenation of l -acetonaphthone with an SCR of 12 300 in a 2-propanol-DMF mixture (1 1, v/v) to afford the chiral alcohol in 97% ee (Fig. 32.35) [113]. This supported complex is separable... 

The Mannich reaction is a three component reaction in which an imine, that was formed from the condensation of an amine with an aldehyde, reacts with a component containing at least one hydrogen atom of pronounced reactivity. It is possible to immobilize every Mannich partner on sohd supports. In combinatorial chemistry the Mannich reaction has been used for the generation of different h-braries (Scheme 3.26). 

While PEG-based supports are widely used for liquid-phase combinatorial chemistry, other non-PEG-based soluble polymers have also been reported for combinatorial applications. A recent review (276) contains an exhaustive list of homo- and copolym-eric soluble supports used in peptide, oligonucleotide, and oligosaccharide synthesis, including combinatorial chemistry. Two of these supports have also been used for small organic molecule synthesis. Homopolymeric polyvinyl alcohol was used in conjunction with PEG for a protection/derivatization strategy in solution (284), and the copolymer between isopropylacrylamide and acrylic acid was used in the catalytic hydrogenation of a Cbz group (285). 

Future trends in reduction of substituted nitrobenzenes will probably be based on novel catalysts. Homogenous transition metal (ruthenium and rhodium) catalysts offer routes to chemospecific reduction of aromatic nitro groups16. Novel catalytic methods involving combinatorial chemistry may offer pathways to new industrial hydrogenation processes, where selective reduction is desired. A number of solution- and solid-phase C /Mo0 redox couple reductions of substituted nitroarenes to the corresponding anilines have been proposed17. 

One object of mathematical chemistry is to associate a unique index to each skeleton (i.e., no hydrogen atoms) molecular diagram (Balaban 1973 King 1977 Randic 1992). The index may be a number, a set of numbers, or a matrix. Hydrogen and other atoms with various valences have since been included and three-dimensional or knotted structures have been treated. In the meantime, however, combinatorial chemistries have accumulated so rapidly that the prospect may be for them to outpace the progress in correlating data to one or another index unless a breakthrough occurs in the latter. 

II.D.3 Photoelectrochemical Hydrogen Production Using New Combinatorial Chemistry Derived Materials... 

Adsorption on silica gel surfaces or silica gels coated with water or thin layers of ionic liquids has been used to immobilize transition metal complexes % ionic interactions and hydrogen bonding. Reversed-phase silica gels were used to retain catalysts by hydrophobic interactions. Support of catalysts on fluorous reversed-phase silica gel by the solvophobic nature of perfluoroalkyl chains is a new and promising approach with potential in catalysis and combinatorial chemistry. 

Other analogs were also prepared from oxomaritidine by hydrogenation to give 24, which on reductive amination with polymer-supported cyanoborohydride afforded a small library of unnatural analogs based on the structure of 25. Obviously, many other derivatives would be possible given the efficiency of this route to the natural products, and clearly many of the intermediates, such as the spirodienone 23, could usefully be diverted to other combinatorial chemistry programs for further elaboration and decoration. 

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