Unsaturated substrates acetophenone

For satisfactory diemo- and stereoselectivity, most catalytic, direct cross-aldol methods are limited to the use of non enolizable (aromatic, a-tert-alkyl) or kineti-cally non enolizable (highly branched, ,/funsaturated) aldehydes as acceptor carbonyls. With aromatic aldehydes, however, enantioselectivity is sometimes moderate, and the dehydration side-product may be important. With regard to the donor counterpart, the best suited pronucleophile substrates for these reactions are symmetric ketones (acetone) and ketones with only one site amenable for enolization (acetophenones). With symmetric cyclic or acyclic ketones superior to acetone, syn/anti mixtures of variable composition are obtained [8b, 11, 19a]. Of particularly broad scope is the reaction of N-propionylthiazolidinethiones with aldehydes, which regularly gives high enantioselectivity of the syn aldol adduct of aromatic, a,fi-unsaturated, branched, and unbranched aldehydes [13]. 

Another complement to enamine catalysis is Br0nsted acid catalysis. Blanche showed that a Hg-BlNOL-derived phosphoric acid catalyzes the aldol reaction to give jy -aldols 162-165 from various ketones [175]. Gratifyingly, the method is suitable for acetophenone, fused cyclic aromatic ketones, and a,(3-unsaturated ketones, substrates that are normally challenging donors in enamine catalysis (Chart 3.22). 

The catalytic properties of the sulfonated diphosphine-stabilized RuNPs and sulfonated diphosphine/cyclodextrin-stabilized RuNPs were compared in the hydrogenation of unsaturated model substrates (styrene, acetophenone, and w-methylanisole) in biphasic liquid-hquid conditions (i.e., ruthenium aqueous colloidal solution and organic substrate no added solvent). Whilst all of these RuNPs displayed suitable performances in catalysis, different activities and selec-tivities were observed. This highhghted that supramolecular interactions on the metallic surface in the presence of a cyclodextrin control the catalytic reactivity of the nanocatalysts. Interestingly the CD acts as a phase-transfer promotor, which... 

The catalytic properties of the sulfonated diphosphine-stabilized Ru NPs and sulfonated diphosphine/CD-stabilized Ru NPs were compared in the hydrogenation of unsaturated model substrates (styrene, acetophenone, and m-methylanisole) in biphasic liquid-liquid conditions (i.e., ruthenium aqueous colloidal solution and organic substrate no added solvent). 

---