Studies On Organocatalyzed Asymmetric Aldol And Other Reactions

Asymmetric organic synthesis is one of the most attractive research areas in organic synthesis. As a new method for asymmetric synthesis, enantioselective organocatalysis has become more and more popular. In this context, the design and synthesis of multifunctional chiral organocatalysts are of great importance. Accordingly, we have prepared a series of bifunctional chiral secondary amine-amides in which one catalyst molecule possesses two reaction-promoting functionalities. Thus, the activity and selectivity can be tuned by a simple modification in the structural motif of the catalyst. The basic structure units of the catalysts are outlined as below.In order to examine the catalytic activity of the new catalysts, we have carried out the direct asymmetric Aldol reaction of tetrahydro-4H-thiopyran-4-one with aldehydes. It has been found that the above catalysts have remarkable activities for this particular reaction. The reactions of aromatic aldehydes with tetrahydro-4H-thiopyran-4-one afford the Aldol adducts in good to excellent yield, with enantioselectivities ranging from 97% to 99% ee.There have been considerable efforts to develop organic reactions using water as an additive or a solvent instead of conventional organic solvents with respect to environmental concerns, safety, and cost. In contrast, there have been relatively few investigations using brine as the reaction media, although the reaction efficiency in brine may be superior to that in water. We examine the asymmetric Aldol reaction with cyclohexanone and aldehyde using tunable and bifunctional organocatalysts in aqueous media. To our delight, we obtain high diastereo- and enantioselectivities in brine with these chiral diamide organocatalysts.α-Substituted phosphonates are particularly important in connection with their remarkable biological activities. They have been found widespread use as enzyme inhibitors, antibacterial agents, anti-HIV agents, botryticides, and haptens for catalytic antibodies. For these reasons, the synthesis ofα-substituted phosphonates and their functionalized derivatives is an important objective. We have initially examined organocatalytic enantioselective synthesis ofα-Hydroxy phosphonates through the reaction of dialkyl phosphates and aldehydes.A series ofα,β-unsaturated aldehydes have been prepared in high yields through Ru-catalyzed cross metathesis reactions of various substituted allyloxy-benzene with (E)-but-2-enal.