Nitrocyclopropanes as Valuable Building Blocks in Organic Synthesis and Biology: Exploring the Origin of the Nitro Group

Cyclopropane derivatives serve as important building blocks in organic synthesis, due to their three-membered stretched ring. Nitro-substituted cyclopropanes (NCPs) represent a special class of donor-acceptor cyclopropanes (DACs) that contain a strong electron-withdrawing nitro group as substituent on the cyclopropyl moiety. Due to the versatile nature of the nitro group, which can be converted into other functional azo groups or heterocyclic scaffolds, NCPs are considered important building blocks in the design of complex organic compounds. Herein, the present review is organized in two main sections focused on the synthesis and application of NCPs. The part containing the synthetic methodologies of NCPs has been further divided into distinct sections based mainly on the nature of the starting materials, such as: a) from nitroalkenes, b) from nitro-bearing diazo compounds, c) from nitroalkanes in combination with alkenes, d) from aminocyclopropanes under oxidative conditions, and e) from various nitro compounds, through miscellaneous processes. In the part concerning the applications and use of NCPs, the categorization includes three main subcategories, concerning their reduction to 1-aminocyclopropane-1-carboxylic acids (ACC), the ring opening of NCPs leading to valuable open-chain heterocycles, and the ring expansion to larger cyclic and heterocyclic compounds.

Asymmetric Synthesis of Chiral Cyclopropanes from Vinyl Sulfoxonium Ylides Catalyzed by a Chiral-at-Metal Rh(III) Complex

A chiral-at-metal Rh(III) complex-mediated [2+1] cyclization of vinyl sulfoxonium ylides with α,β-unsaturated 2,2-acylimidazoles has been demonstrated for the first time. This work provides a practical approach for assembling 1,2,3-trisubstituted chiral cyclopropane with alkyl structural units, which had advantages such as a wide range of substrates, good functional group tolerance, and mild reaction conditions. In addition, further amplification experiments and transformation of cycloaddition products were carried out to highlight the practicality of the method.

Asymmetric Synthesis of Spiro-3,3'-cyclopropyl Oxindoles via Vinylogous Michael Initiated Ring Closure Reaction

A novel organocatalytic cascade approach for the synthesis of spiro-cyclopropyl oxindole derivatives has been developed. The methodology is based on asymmetric vinylogous Michael addition of 4-nitroisoxazole derivatives to N-Boc isatylidene malonates followed by intramolecular alkylation. Its remarkable stereocontrol, wide substrate scope, and scalability highlight this new developed strategy. Moreover, this work represents the first example of vinylogous Michael initiated ring closure (MIRC) reaction for the synthesis of chiral 3,3'-cyclopropyl oxindole.

Synthesis of chiral pyrimidine-substituted diester D-A cyclopropanes via asymmetric cyclopropanation of phenyliodonium ylides

A highly enantioselective cyclopropanation to synthesize pyrimidine-substituted diester D-A cyclopropanes is reported. Various N1-vinylpyrimidines react well with phenyliodonium ylides, delivering chiral cyclopropanes in up to 97% yield with up to 99% ee. Through simple [3+2] annulation with benzaldehyde or ethyl glyoxylate, different chiral pyrimidine nucleoside analogues with a sugar ring could be obtained.

The Synthesis of Hydrobenzoin-Based Monoaza Crown Ethers and Their Application as Recyclable Enantioselective Catalysts

Abstract

New recyclable monoaza-15-crown ethers have been synthesized starting from (R,R)-(+)- and (S,S)-(−)-hydrobenzoin. These macrocycles proved to be efficient and reusable phase transfer catalysts in a few asymmetric reactions under mild conditions. The asymmetric epoxidation of trans-chalcone took place with up to 81% ee, while using other chalcone derivatives, the products were formed with 68–88% ee. The hydrobenzoin-based lariat ethers were also tested in the cyclopropanation of a few electron deficient olefins using diethyl bromomalonate to afford the product with good enantioselectivities (54–75% ee). The catalysts were recovered by salt formation, followed by extraction, and were reused without the loss of the activity and effect on the enantioselectivity.

Graphic Abstract

The synthesis of hydrobenzoin-based monaza crown ethers and their application as recyclable enantioselective catalysts.

Diastereoselective synthesis of α-dicarbonyl cyclopropanes via a lanthanide amide-catalysed reaction

Lanthanide bis(trimethylsilyl)amides, [(Me₃Si)₂N]₃Ln(μ-Cl)Li(THF)₃, were used as efficient catalysts for a one-pot reaction of α-ketoesters, dialkyl phosphite, and activated alkenes to produce α-dicarbonyl cyclopropanes in moderate to high yields. The reaction was stereoselective and the two adjacent carbonyls linked to the cyclopropane were in the cis-configuration. The high efficiency of the lanthanide amide in catalysing the reaction is the result of the cooperation between the lanthanide metal centre and the N(SiMe₃)₂ anion.