Solvents enantioselective organic synthesis

The HDA reaction allows for rapid access to chiral six-membered heterocyclic structures that serve as valuable intermediates in organic synthesis. The first highly enantioselective HDA reaction promoted by a chiral hydrogen bond donor was reported from the Rawal laboratory. While investigating the cycloaddition reactions of amino-siloxy diene 115, it was observed that this diene was exceptionally reactive to heterodienophiles, and underwent HDA reactions with various aldehydes at room temperature, even in the absence of any added catalyst (Scheme 6.14). Subsequent treatment of the intermediate cycloadducts (116) with acetyl chloride afforded the corresponding dihydro-4-pyrones (117) in good overall yields [101]. Further studies of this reaction revealed a pronounced solvent effect,... 

Due to their ready availability and the ease with which they can be handled, hydrolytic enzymes have been widely applied in organic synthesis. They do not require coenzymes, are reasonably stable, and often tolerate organic solvents. Their potential for regioselective and especially for enantioselective synthesis makes them valuable tools [10, 14, 16, 19]. 

Okahata, Y, Fujimoto, Y, and Ijiro, K., A lipid-coated lipase as an enantioselective ester synthesis catalyst in homogeneous organic solvents, J. Org. Chem., 60, 2244-2250, 1995. 

Control of selectivity (chemo, regio, stereo, and enantioselectivity) is among the most important objective in organic synthesis. The efficient use of reaction conditions (temperature, time, solvent, etc.), kinetic or thermodynamic control, protecting or activating groups (for example chiral auxiliaries), and catalysts (including chiral catalysts) have all been used to obtain the desired isomer. 

CILs are a subclass of ILs in which the cation or the anion (or both) may be chiral. The chirality can be either central, axial, or planar. It is well established that chirality plays an important role in chemistry. Over the last few years, research for new chiral selectors, solvents, and materials based on CILs has become a topic of increasing interest. A growing number of CILs have been designed, synthesized, and utilized for potential applications in chiral discrimination and separation [24], asymmetric catalysis and synthesis [25], as well as optical resolution of racemates [26]. Because of their high-resolution abilities and liquidus properties, CILs can be used as either chiral agents in regular solvent, or chiral solvents, or both simultaneously. With the rapid development of CILs, these new chiral solvents have the potential to play an important role in enantioselective organic chemistry, chiral separation chemistry, and chiral materials chemistry. Thus, their role in these fields is expected to expand tremendously. 

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