Synthesis of a bipyridine-derived achiral thiourea trifluoromethanesulfonic acid salt and its application as an additive in organocatalytic asymmetric reactions

Asymmetric Supramolecular Organocatalysis: A Complementary Upgrade to Organocatalysis

“…Subsequently, Demir and Basceken explored the combination of proline and thiourea–bipyridine trifluoromethanesulfonic acid salt 20b and tested its effectiveness in supramolecular organocatalytic asymmetric reactions such as the aldol, Michael, and Mannich reactions in polar protic media, because there were great interest and potential advantages in carrying out organic reactions in water or other aqueous media (Scheme ) . Unlike in the case of the aldol reaction, attempted Michael addition between aldehydes 10 and nitroalkenes 2 in the presence of this water‐soluble catalyst did not afford any product in water.…”

“…Because there were great interest and potential advantages in carrying out organic reactions in water and other aqueous media, the authors extended their work and explored bipyridine‐derived achiral thiourea 20d in its water‐soluble form, salt 20b , and tested its effectiveness for LLB‐A reactions in water without any organic solvent (Scheme ) , . Various examples were studied, and the aldol products 53 were obtained in comparably good yields (60–85 %) and with very high selectivity (up to 99 % ee ).…”

“…Basceken's method involving l ‐proline ( 7a ) and thiourea–bipyridinium trifluoromethanesulfonate salt 20b as a supramolecular organocatalyst system for asymmetric LLB‐A reaction in water. Reprinted from ref . with permission from Elsevier.…”

Asymmetric Aldol Reaction Catalyzed by l‐Proline and Achiral Thiourea Fluoroboric Acid Salt

“…Acid additives can influence the outcome of enamine‐mediated reactions; however, only a few screening studies of acid additions to thiourea organocatalysts are available in the literature 4e,11 . The reaction between cyclohexanone and 4‐nitrobenzaldehyde was selected as a standard model reaction for screening of more effective acid additives to thiourea.…”

L-proline/cholesterol and diosgenin based thiourea cooperative system for the direct asymmetric aldol reaction in the presence of water

“…We have successfully investigated and determined that the self-assembled prolinethioureasupramolecular complex was an efficient organocatalyst for a direct enantioselective aldol reaction in nonpolar solvents such as hexane [7]. Also, researchers have shown that the use of suitable additives, such as water [8][9][10], chiral alcohols [11,12], thioureas [13][14][15][16][17], thiouronium salts [18], imidazolium salts [19], and guanidinium salts [20] has been documented as a powerful method to accelerate the rate of reaction and improve the stereoselectivity of aldol reactions.…”