The Regiocontrollable Enantioselective Synthesis of Chiral Trifluoromethyl-Containing Spiro-Pyrrolidine-Pyrazolone Compounds via Amino-Regulated 1,3-Proton Migration Reaction

Developments in Organocatalysis Transformations of Unsaturated Pyrazolones

Unsaturated pyrazolones can participate in organocatalytic reactions with various substrates to form spiro-cyclic pyrazolones, and fuzed-pyrazolone heterocycles. The present review describes progress since 2013 in the organocatalysis transformations of unsaturated pyrazolones. Pyrazolones are prevalent structural motifs in a wide variety of natural products and drug or drug-like molecules. A series of nitrogen-containing pyrazolones exhibits anticancer, antimicrobial, anti-inflammatory, anticonvulsant, antidepressant, antidiabetic, and antipyretic activities. Especially, chiral spiro-cyclic pyrazolones are recognized as targets in natural products and clinical pharmaceuticals. Organocatalytic systems are powerful and reliable approaches that allow us to build structurally complex molecules in an enantioselectively and diastereoselectively manner. Avoiding the use of transition metal catalysts, readily available bifunctional organocatalysts, and the performance of the reaction at ambient temperature are other advantages of these catalytic systems. Despite considerable progress in this field, it is still one of the challenging goals for chemists to make new biologically active heterocyclic molecules.

Synthesis of difluoromethylated spiropyrazolones via [3 + 2] cycloaddition of difluoroacetohydrazonoyl bromides with alkylidene pyrazolones

An effective [3 + 2] cycloaddition reaction of difluoromethyl or trifluoromethyl hydrazonoyl bromides with alkylidene pyrazolones was disclosed. This method provides an efficient approach for accessing a variety of highly functionalized fluoroalkyl spiropyrazolones in good yields. This protocol also features some advantages such as easily available and stable substrates, simple operation procedures, and atom and step economy. The formation of (cis)- and (trans)-products was discussed.

Asymmetric Umpolung (3+2) Cycloadditions of Iminoesters with α,β-Unsaturated-2-acyl Imidazoles for the Synthesis of Substituted Pyrrolidines

An enantioselective (3+2) cycloaddition reaction of iminoesters occurring with opposite regioselectivity is reported. This reaction provides chiral polysubstituted pyrrolidines with high enantioselectivities (up to 97%), diastereoselectivities (>20:1), and yields (up to 99%). Interestingly, changing the alpha-substituents of the iminoesters from an aryl to an aliphatic (benzyl) group or hydrogen resulted in the formation of normal (3+2) cycloaddition products, also in excellent enantioselectivities.

Synthesis of α,γ-Chiral Trifluoromethylated Amines through the Stereospecific Isomerization of α-Chiral Allylic Amines

Chiral γ-branched aliphatic amines are present in a large number of pharmaceuticals and natural products. However, enantioselective methods to access these compounds are scarce and mainly rely on the use of designed chiral transition-metal complexes. Herein, we combined an organocatalytic method for the stereospecific isomerization of chiral allylic amines with a diastereoselective reduction of the chiral imine/enamine intermediates, leading to γ-trifluoromethylated aliphatic amines with two noncontiguous stereogenic centers, in excellent yields and high diastereo- and enantioselectivities. This approach has been used with primary amine substrates. This approach also provides a new synthetic pathway to chiral trifluoromethylated scaffolds, of importance in medicinal chemistry. Additionally, a gram-scale reaction demonstrates the applicability of this synthetic procedure.