Thiourea derived catalysts bifunctional

Modified Cinchona alkaloids catalysts have been developed in the last two decades to enhance further the bifunctional mode of the catalyst. Derivations at the C(9)-OH group, replacement of quinoline C(6 )-OCH3 with a hydroxyl group to enhance hydrogen bonding, syntheses of bis-Cinchona alkaloids, and development of thiourea-derived Cinchona alkaloids are most notable. 

Scheme 8.19 Supported thiourea derivative as chiral bifunctional catalyst.

Some bifunctional hydrogen-bond donor/Brpnsted base catalysts are shown in Figures 2.39 and 2.40. They comprise chiral amino alcohols and amino phenols, chiral amine-thiourea derivatives, and chiral guanidines, among others. In the absence of detailed experimental NMR or kinetic studies [179], most of our... 

Miao, Chen, and coworkers have reported an efficient enantioselective Biginelli reaction catalyzed by a chiral bifunctional primary amine-thiourea derivative 43 with a carbohydrate in the catalyst skeleton and using an external Brpnsted acid in a cooperative way, with t-BuNH TFA as additive (Scheme 9.15) [54]. This protocol renders a wide range of optically active DHPMs 44 in high yields and with good to excellent enantioselectivities (up to 99% ee). 

Furthermore, Jacobsen s group reported the development of a new thiourea catalyst for the enantioselective bicycliza-tion of hydroxylactams [54]. The enantioselective cationic polycyclization reactions catalyzed by bifunctional thiourea derivatives appear to engage stabilizing jt-cadon interactions as a principal element of enantioselectivity (Scheme 9.41). 

Using the addition of dimethyl malonate to nitro-olefms as the model reaction, Connon et al. [72] in 2(X)5 reported a highly functionahzed Cinchona alkaloid-derived chiral thiourea. Key functional groups were identified to enhance the catalyst s stereodirecting properties. Aside from the advantage of a bifunctional Cinchona alkaloid... 

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