Asymmetric cooperative catalysis in the conjugate addition of pyrazolones to nitroolefins and subsequent dearomative chlorination

Enantioselective Michael Addition of Pyrazolin-5-ones to Nitroalkenes Catalyzed by Novel Squaramide Organocatalyst

Abstract:

A newly tertiary amine-thiourea organocatalyst has successfully developed and applied into the asymmetric Michael addition of pyrazolin-5-one to nitroalkenes. The catalyst system performed well with a low catalyst loading of 5 mol% under mild reaction conditions. A series of synthetically and pharmaceutically useful chiral pyrazolone derivatives were obtained in high yields (up to 95%) with good enantioselectivities (up to 88 % ee).

Highly enantioselective Michael addition of pyrazolin-5-ones to nitroolefins catalyzed by cinchona alkaloid derived 4-methylbenzoylthioureas

Cinchona alkaloid-derived 4-methyl/nitro benzoylthioureas were synthesized, which smoothly catalyzed the asymmetric Michael addition of pyrazolin-5-ones to nitroolefins. The results showed that electronic effects of substituents in the benzene ring of benzoylthioureas have subtle influences on their catalytic abilities and electron donating methyl group is favored than electron withdrawing nitro group. Preliminary Hartree-Fock calculations revealed that in the catalytic cycle, hydrogen bond energies of the complex formed with 4-methylbenzoylthioureas are about 0.19 to 1.56 kcal/mol higher than with the corresponding 4-nitrobenzoylthioureas. 4-Methylbenzoylthioureas were identified as the most effective catalysts that promoted asymmetric Michael addition of pyrazolin-5-ones to nitroolefins to give the S- or R-products with high enantioselectivities.

Organocatalytic Asymmetric Decarboxylative Mannich Reaction of β-Keto Acids with Cyclic α-Ketiminophosphonates: Access to Quaternary α-Aminophosphonates

An organocatalytic asymmetric decarboxylative Mannich reaction of β-keto acids with cyclic α-ketiminophosphonates has been developed. By using saccharide-derived bifunctional amine-thiourea catalysts bearing an axial chiral binaphthyl scaffold, a wide range of quaternary α-amino-γ-oxophosphonates were obtained in up to 93% yield and >99% ee. Furthermore, two interesting α-aminophosphonate derivatives were synthesized from the corresponding decarboxylative Mannich product via simple transformations.

Pyrazolone: a powerful synthon for asymmetric diverse derivatizations

This feature article reports recent advances in the asymmetric diverse derivatizations of the pyrazolone scaffold.

Asymmetric chlorination of 4-substituted pyrazolones catalyzed by natural cinchona alkaloid

A natural quinidine catalyzed asymmetric chlorination of 4-substituted pyrazolones was revealed in high yield and excellent enantioselectivity.

Combining silver- and organocatalysis: an enantioselective sequential catalytic approach towards pyrano-annulated pyrazoles

A one-pot asymmetric Michael addition/hydroalkoxylation sequence, catalyzed by a sequential catalytic system consisting of a squaramide and a silver salt, provides a new series of chiral pyrano-annulated pyrazole derivatives in excellent yields (up to 95%) and high enantioselectivities (up to 97% ee).

Asymmetric synthesis of pyrazoles and pyrazolones employing the reactivity of pyrazolin-5-one derivatives

The various catalytic asymmetric strategies employing organo- and metal-catalysts utilized pyrazolin-5-one derivatives for the synthesis of potentially bioactive enantiopure pyrazoles and pyrazolones are presented.