Synthesis of 5-alkyl-5-aryl-γ-lactams from 1-aryl-substituted nitroalkanes and methyl acrylate via Michael addition and reductive lactamization

Copper-Catalyzed α-Arylation of Nitroalkanes with (Hetero)aryl Bromides/Iodides

α-Aryl substituted nitroalkanes are valuable synthetic building blocks that can be easily converted into α-aryl substituted aldehydes, ketones, carboxylic acids, as well as amines. Herein, an efficient Cu/oxalamide-catalyzed coupling between nitroalkanes and (hetero)aryl halides (Br, I) was developed to direct access highly diverse α-aryl substituted nitroalkanes. Compared with the current state of art, this protocol is more environmentally friendly and practical for synthetic chemists. This approach is characterized by a broad substrate scope on both nitroalkane part (primary nitroalkanes and nitromethane) and sp2 halide part ((hetero)aryl bromides/iodides and alkenyl bromides/iodides). The excellent functional group tolerance was observed, which would enable real world synthetic applications. More importantly, TON of current transformation reached to 3640, when some aryl iodides were used as coupling partners. This represents currently the highest catalyst turnover for transition-metal catalyzed α-arylation of nitroalkanes. Furthermore, the successful application in late-stage modification of complex molecules and synthesis of a known retinoid X receptor (RXR) antagonist exemplified its synthetic potential.

Organocatalytic Michael Addition of Unactivated α-Branched Nitroalkanes to Afford Optically Active Tertiary Nitrocompounds

The direct, asymmetric conjugate addition of unactivated α-branched nitroalkanes is developed based on the combined use of chiral amine/ureidoaminal bifunctional catalysts and a tunable acrylate template to provide tertiary nitrocompounds in 55-80% isolated yields and high enantioselectivity (e.r. up to 96:4). Elaboration of the ketol moiety in thus obtained adducts allows a fast entry to not only carboxylic and aldehyde derivatives but also nitrile compounds and enantioenriched 5,5-disubstituted γ-lactams.

Comprehension of the α-Arylation of Nitroalkanes

Background:

α-Aryl substituted nitroalkanes are important synthetic intermediates for the preparation of pharmaceutical molecules, natural products, and functional materials. Due to their scare existence in Nature, synthesis of these compounds has attracted the attention of synthetic and medicinal chemists, rendering α-arylation of nitroalkanes of an important research topic. This article summarizes the important advances of α- arylation of nitroalkanes since 1963.

Results:

After a brief introduction of the synthetic application and the reactions of nitroalkanes, this article reviewed the synthetic methods for the α-arylated aliphatic nitro compound. The amount of research on α-arylation of nitroalkanes using various arylation reagents and the discovery of elegant synthetic approaches towards such skeleton have been discussed. This review described these advances in two sections. One is the arylation of non-activated nitroalkanes, with an emphasis on the application of diverse arylation reagents; the other focuses on the arylation of activated nitroalkanes, including dinitroalkanes, trinitroalkanes, α-nitrosulfones, α-nitroesters, α-nitrotoluenes, and α-nitroketones. The synthetic application of these methods has also been presented in some cases.

Conclusion:

In this review, we described the progress of α-arylation of nitroalkanes. Although the immense amount of research on α-arylation of aliphatic nitro compounds has been achieved, many potential issues still need to be addressed, especially the asymmetric transformation and its wide application in organic synthesis.

Catalytic Asymmetric Cycloadditions of Silyl Nitronates Bearing α-Aryl Group

1,3-Dipolar cycloadditions of 2-alkylacroleins or atropaldehyde with triisopropylsilyl nitronates bearing an α-aryl group produced 3-aryl-2-isoxazolines having a chiral quaternary center in up to 94% ee and up to 88% yield with the aid of Corey's oxazaborolidine catalyst. Specifically, the TIPS nitronate with an α-(p-methoxyphenyl) group gave mainly the 2-isoxazolines having an all-carbon quaternary center.