Enantioselective Copper-Catalyzed Synthesis of Trifluoromethyl-Cyclopropylboronates

Nitrogen-Based Organofluorine Functional Molecules: Synthesis and Applications

Fluorine and nitrogen form a successful partnership in organic synthesis, medicinal chemistry, and material sciences. Although fluorine-nitrogen chemistry has a long and rich history, this field has received increasing interest and made remarkable progress over the past two decades, driven by recent advancements in transition metal and organocatalysis and photochemistry. This review, emphasizing contributions from 2015 to 2023, aims to update the state of the art of the synthesis and applications of nitrogen-based organofluorine functional molecules in organic synthesis and medicinal chemistry. In dedicated sections, we first focus on fluorine-containing reagents organized according to the type of fluorine-containing groups attached to nitrogen, including N-F, N-RF, N-SRF, and N-ORF. This review also covers nitrogen-linked fluorine-containing building blocks, catalysts, pharmaceuticals, and agrochemicals, underlining these components' broad applicability and growing importance in modern chemistry.

Fluorohydrins and where to find them: recent asymmetric syntheses of β-fluoro alcohols and their derivatives

Fluorohydrins - or β-fluorinated alcohols - and their fluorinated group derivatives are a biologically relevant class of compounds, with applications ranging from PET tracers to cancer therapeutics. Recent efforts have unlocked asymmetric access to these related motifs through reactions of carbonyls, alkenes, organoboranes, and epoxides or transformations such as cyclizations or ring expansions. The present work provides an overview of synthetic approaches to various fluorohydrins that have been explored in the past decade, as well as selected examples of these syntheses applied to medicinal chemistry.

Advances in the Synthesis of Cyclopropylamines

Cyclopropylamines are an important subclass of substituted cyclopropanes that combine the unique electronic and steric properties of cyclopropanes with the presence of a donor nitrogen atom. In addition to their presence in a diverse array of biologically active compounds, cyclopropylamines are utilized as important synthetic intermediates, particularly in ring-opening or cycloaddition reactions. Consequently, the synthesis of these compounds has constituted a significant research topic, as evidenced by the abundant published synthetic methods. In addition to the widely used Curtius rearrangement, classical cyclopropanation methods have been adapted to integrate a nitrogen function (Simmons-Smith reaction, metal-catalyzed reaction of diazo compounds on olefins, Michael-initiated ring-closure reactions) with significant advances in enantioselective synthesis. More recently, specific methods have been developed for the preparation of the aminocyclopropane moiety (Kulinkovich reactions applied to amides and nitriles, addition to cyclopropenes, metal-catalyzed reactions involving C-H functionalization, ...). The topic of this review is to present the different methods for the preparation of cyclopropylamine derivatives, with the aim of covering the methodological advances as best as possible, highlighting their scope, their stereochemical aspects and future trends.

Recent advances in asymmetric synthesis via cyclopropanol intermediates

Cyclopropanols have attracted significant attention in organic synthesis as versatile three-carbon synthons, as this readily available class of donor-activated cyclopropanes undergoes miscellaneous transformations, either via ring-opening or with retention of the cyclopropane ring. This review summarizes stereoselective and stereoretentive transformations suitable for asymmetric synthesis. The utility of cyclopropanols is discussed for two main strategies: (i) substrate-controlled transformations using enantiomerically enriched cyclopropanol intermediates through a traditional approach, and (ii) the use of nonchiral or racemic cyclopropanols, where asymmetric induction is achieved through a chiral catalyst, representing a direction that has recently emerged.

Cu-Catalyzed Diastereo- and Enantioselective Synthesis of Borylated Cyclopropanes with Three Contiguous Stereocenters

Direct synthesis of enantioenriched scaffolds with multiple adjacent stereocenters remains an important yet challenging task. Herein, we describe a highly diastereo- and enantioselective Cu-catalyzed alkylboration of cyclopropenes, with less reactive alkyl iodides as electrophiles, for the efficient synthesis of tetra-substituted borylated cyclopropanes bearing three consecutive stereocenters. This protocol features mild conditions, a broad substrate scope, and good functional group tolerance, affording an array of chiral borylated cyclopropanes in good to high yields with excellent diastereo- and enantioselectivities. Detailed mechanistic experiments and kinetic studies were conducted to elucidate the reaction pathway and the rate-determining step of the reaction. DFT calculations revealed that the π···π stacking interaction between the phenyl groups on the substrate and the phosphorus ligand, along with the smaller distortion in the CuL-Bpin part, contributed to the high diastereo- and enantioselectivities. The synthetic utility of the protocol was showcased by the facile synthesis of some valuable chiral cyclopropanes with multiple chiral centers.

Iron(III)-based metalloradical catalysis for asymmetric cyclopropanation via a stepwise radical mechanism

Metalloradical catalysis (MRC) exploits the metal-centred radicals present in open-shell metal complexes as one-electron catalysts for the generation of metal-stabilized organic radicals-key intermediates that control subsequent one-electron homolytic reactions. Cobalt(II) complexes of porphyrins, as stable 15e-metalloradicals with a well-defined low-spin d7 configuration, have dominated the ongoing development of MRC. Here, to broaden MRC beyond the use of Co(II)-based metalloradical catalysts, we describe systematic studies that establish the operation of Fe(III)-based MRC and demonstrate an initial application for asymmetric radical transformations. Specifically, we report that five-coordinate iron(III) complexes of porphyrins with an axial ligand, which represent another family of stable 15e-metalloradicals with a d5 configuration, are potent metalloradical catalysts for olefin cyclopropanation with different classes of diazo compounds via a stepwise radical mechanism. This work lays a foundation and mechanistic blueprint for future exploration of Fe(III)-based MRC towards the discovery of diverse stereoselective radical reactions.

Synthesis of di/trifluoromethyl cyclopropane-dicarbonitriles via [2+1] annulation of fluoro-based diazoethanes with (alkylidene)malononitriles

Herein, we describe a [2+1] annulation reaction of di/trifluorodiazoethane with (alkylidene)malononitriles. This protocol offers a streamlined synthesis of a wide range of stereospecific and densely functionalized difluoromethyl and trifluoromethyl cyclopropane-1,1-dicarbonitriles. Further functional group interconversions or skeletal elaborations afford structurally distinct cyclopropyl variants.

Pentafluorocyclopropanation of (Hetero)arenes Using Sulfonium Salts: Applications in Late-Stage Functionalization

The evaluation of the pentafluorocyclopropyl group as a chemotype in crop protection and medicinal chemistry has been hampered in the past by the lack of suitable methodologies that enable the practical incorporation of this moiety into advanced synthetic intermediates. Herein, we report the gram-scale synthesis of an unprecedented sulfonium salt, 5-(pentafluorocyclopropyl)dibenzothiophenium triflate, and its use as a versatile reagent for the photoinduced C-H pentafluorocyclopropylation of a broad series of non-previously functionalized (hetero)arenes through a radical mediated mechanism. The scope and potential benefits of the protocol developed are further demonstrated by the late-stage introduction of the pentafluorocyclopropyl unit into biologically relevant molecules and widely used pharmaceuticals.

Asymmetric Synthesis of Tertiary and Secondary Cyclopropyl Boronates via Cyclopropanation of Enantioenriched Alkenyl Boronic Esters

The cyclopropanation of alkenyl boronates and subsequent derivatization of the boronate handle are a convenient strategy to quickly build molecular complexity and access diverse compounds with a high sp³ fraction. Herein, we describe the asymmetric cyclopropanation of enantioenriched hydrobenzoin-derived alkenyl boronic esters toward the synthesis of tertiary and secondary cyclopropyl boronates.