Binaphthyl-Derived Mono-, Bi- and Multi-Functional Lewis and Brønsted Base Organocatalysts: A New Vista for Asymmetric Synthesis

Organocatalytic diastereo- and enantioselective conjugate addition of pyrazol-3-ones to 3-trifluoroethylidene oxindoles with a newly developed squaramide catalyst

“…On the basis of our above experimental observations and previous reported elegant works, 2–4 a proposed reaction mechanism is elucidated in Fig. 1.…”

“…As a comparison, we also examined the known privileged chiral catalysts, such as chiral spirobiindane-derived thioureas ( 9b ), 6 h chiral squaramide catalysts ( 9c and 9d ) 4 and chiral phosphoric acid ( 9e ) 6 a (entries 10–13) in the model reaction to show their effectiveness in terms of reactivity and stereoselectivity. However, no better result was obtained.…”

“… 3 In particular, chiral bifunctional squaramide catalysts with cinchonine and BINOL backbones represent a great achievement in asymmetric synthesis, as they provide excellent stereoselectivity in many organic reactions. 4 Notwithstanding this remarkable progress, there are still many synthetically useful transformations that remain unattainable in an asymmetric manner. 5 The chiral framework of the catalyst plays a crucial role in its performance, thus the development of new and efficient bifunctional squaramide catalysts with different backbones is still highly valuable and desirable for asymmetric transformations.…”

Enantioselective Organocatalyzed Transformations of β-Ketoesters

“…The employment of chiral hydrogen bond donors is a major activation strategy within asymmetric organocatalysis. There are several valuable reviews ,,− that highlight this subject. The most widely employed hydrogen-bonding organocatalysts include chiral-(thio)­ureas, diols, phosphoric acids, and various cinchona alkaloid derivatives.…”