Bicyclo Pentane Research Articles

Metal- and Photocatalyst-Free Sulfonylcyanation of [1.1.1]Propellane with Sulfonyl Cyanide

Background: Bicyclo[1.1.1]pentanes (BCPs), recognized as bioisosteres for para-disubstituted benzene rings, have gained prominence as valuable bioactive scaffolds in drug research. Methods: This study describes a radical-coupling method for the synthesis of sulfonyl-, cy-ano-substituted BCPs from sulfonyl cyanide and [1.1.1]propellane. In this study, the synthet-ic schemes were designed to show the chemical reactions. Nuclear Magnetic Resonance (NMR) and Mass Spectrometry (MS) were used to identify and characterize the final com-pounds. Results: This method does not require photocatalysts, metals, or light, generating BCP ni-triles as a useful building block. The synthetic potential of this mild protocol was showcased by the diverse transformations. Conclusion: This versatile method significantly expands the range of BCP-type bioisosteres that can be generated.

Halogen Bonding Initiated Difunctionalization of [1.1.1]Propellane via Photoinduced Polarity Match Additions

AbstractBicyclo[1.1.1]pentane (BCP), recognized as a bioisostere for para‐disubstituted benzene, has gained widespread interest in drug development due to its ability to enhance the physicochemical properties of pharmaceuticals. In this work, we introduce a photoinduced, halogen bonding‐initiated, metal‐free strategy for synthesizing various BCP derivatives. This method involves the generation of nucleophilic α‐aminoalkyl radicals via halogen‐bonding adducts. These undergo selective radical addition to [1.1.1]propellane, yielding electrophilic BCP radicals that subsequently participate in polarity‐matched additions, culminating in the difunctionalization of bicyclopentane. The versatility and practicality of this metal‐free approach are underscored by its broad substrate scope, which includes late‐stage functionalization and a series of valuable transformations, all conducted under mild reaction conditions.

Photocatalytic Diheteroarylation of [1.1.1]Propellane for the Construction of 1,3-Diheteroaryl Bicyclo[1.1.1]pentanes.

Herein, we report a visible light-induced diheteroarylation reaction of [1.1.1]propellane to synthesize 1,3-diheteroaryl bicyclo[1.1.1]pentanes (BCPs). In this approach, heteroaryl radicals are generated from heteroaryl halides via photocatalysis and subsequently added to [1.1.1]propellane. The in situ generated BCP radicals are then trapped by various heterocycles to furnish 1,3-diheteroaryl BCPs. Notably, this strategy features metal-free, mild conditions and utilizes inexpensive catalyst. For the first time, the diheteroarylation of [1.1.1]propellane could be achieved via a radical strategy, allowing for the efficient synthesis of 1,3-diheteroaryl BCPs with various applications in organic and medicinal chemistry.

Benzyl Alcohol Functionalization of [1.1.1]Propellane with Alkanes and Aldehydes.

Bicyclo[1.1.1]pentanes (BCPs) play a crucial role in drug discovery research as C(sp3)-rich bioisosteres of benzene rings. However, the preparation of BCPs with strong alkane C(sp3)-H bonds has not been reported to date. In this study, we reported a method for light-induced benzyl alcohol functionalization of [1.1.1]propellane with aliphatic hydrocarbons (which have not previously been explored for this purpose) and aldehydes under metal- and photocatalyst-free conditions. The BCP products could be transformed into various useful derivatives, demonstrating the utility of the method. Notably, we achieved the synthesis of functionalized BCPs with simple alkanes.

Synthesis of SCD3-containing bicyclo[1.1.1]pentanes enabled by photocatalyzed difunctionalization of [1.1.1]propellane

Bicyclo[1.1.1]pentanes (BCPs) have emerged as appealing bioisosteres for para-substituted benzene rings in drug design. In this study, we report an intermolecular photocatalytic addition of [1.1.1]propellane and S-(methyl-d3) arylsulfonothioates to synthesize novel deuterium-containing BCPs derivatives via energy transfer processes (EnT). This efficient and green protocol provides an access to introduce deuterium into BCP scaffolds and enriches the present library of BCPs compounds for drug design.

Direct Diazoarylation of [1.1.1]Propellane with Arenediazonium Salts: A Modular Assembly of Arylated Diazo Bicyclo[1.1.1]pentanes.

A mild and concise diazoarylation of [1.1.1]propellane is described, which provides a modular approach to arylated diazo bicyclopentanes (BCPs). This reaction proceeds smoothly under basic conditions without requiring other additives or catalysts. The substrate scope shows that various electron-withdrawing and electron-donating groups are tolerated, and the subsequent modifications provide a novel avenue for assembling arylamino-BCP analogs.

Photocatalytic Decarboxylative Alkylation of Cyclic Imine-BF3 Complexes: A Modular Route to Functionalized Azacycles.

Alkyl radicals generated via an acridine photocatalyzed decarboxylation reaction of feedstock carboxylic acids engage with a range of cyclic imine-BF3 complexes to provide α-functionalized azacycles in an operationally simple process. A three-component variant of this transformation incorporating [1.1.1]propellane as an additional reaction partner enables the synthesis of valuable bicyclopentane (BCP)-containing azacycles. Reactions exhibit good functional group compatibility, enabling late-stage modification of complex bioactive molecules.

Photochemical tandem reaction of nitrogen containing heterocycles, bicyclo[1.1.1]pentane, and difluoroiodane(III) reagents.

A visible light-induced difluoroalkylation/heteroarylation of [1.1.1]propellane with nitrogen containing heterocycles and difluoroiodane(III) reagents was achieved. Various heteroarenes and difluoroiodane(III) reagents exhibited good compatibility, yielding the desired products in moderate to good yields. The accessibility of the reagents and the mild reaction conditions establish this method as an alternative and practical strategy for accessing diverse 1-difluoroalkyl-3-heteroaryl bicyclo[1.1.1]pentanes (BCPs).

Photoinduced C(sp3)-H Bicyclopentylation Enabled by an Electron Donor-Acceptor Complex-Mediated Chemoselective Three-Component Radical Relay.

The photoredox electron donor-acceptor (EDA) complex-mediated radical coupling reaction has gained prominence in the field of organic synthesis, finding widespread application in two-component coupling reactions. However, EDA complex-promoted multi-component reactions are not well developed with only a limited number of examples have been reported. Herein, we report a photoinduced and EDA complex-promoted highly chemoselective three-component radical arylalkylation of [1.1.1]propellane, which allows the direct functionalization of C(sp3)-H with bicyclo[1.1.1]pentanes (BCP)-aryl groups under mild conditions. A variety of unnatural α-amino acids, featuring structurally diversified 1,3-disubstituted BCP moieties, were synthesized in a single-step process. Notably, leveraging the high tension release of [1.1.1]propellane, the highly unstable transient aryl radical undergoes rapid conversion into a relatively stable tertiary alkyl transient radical, and consequently, the competing side-reaction of two-component coupling was entirely suppressed. The strategic use of this transient radical conversion approach would be useful for the design of diverse EDA complex-mediated multi-component reactions. It is noteworthy that the highly chemoselective late-stage incorporation of the 1,3-disubstituted BCP pharmacophores into peptides was achieved both in liquid-phase and solid-phase reactions. This advancement is anticipated to have significant application potential in the future development of peptide drugs.

Photoinduced Multicomponent Heteroarylation of [1.1.1]Propellane with Katritzky Pyridinium Salts.

(Hetero)arylated bicyclo[1.1.1]pentanes (BCPs) are important for the construction of complex druglike target molecules. Herein, we developed a method for light-induced, Cs2CO3-promoted homolytic cleavage of pyridinium C-N bonds for generating alkyl radicals from amino acid-derived Katritzky salts and use of the radicals for functionalization of [1.1.1]propellane to rapidly generate (hetero)arylated BCPs. The method features excellent functional group tolerance and a broad substrate scope and can be used to functionalize structurally complex natural products.

A General Approach for the Synthesis of Cyanoisopropyl Bicyclo[1.1.1]pentane (BCP) Motifs by Energy Transfer Process.

Bicyclo[1.1.1]pentane (BCP) heteroaryls make up an important class of BCP derivatives in drug discovery. Herein, we report the visible-light-mediated synthesis of cyanoisopropyl BCP-heteroaryls motifs from N-containing heterocycles, [1.1.1]propellane, and AIBN (2,2'-azobis(isobutyronitrile)) through three-component cascade reaction. Importantly, this protocol is compatible with pyrazinones, quinoxaline-2(1H)-one, azauracils, quinoline derivatives, and imidazo[1,2-b]pyridazine, as well as various phenyl disulfide derivatives; thus, this operationally simple and general methodology could enable rapid library generation of sought-after BCP derivatives for drug development.

Recent Progress in Accessing Multi-functionalized Caged Hydrocarbons: En Route to Highly Functionalized Saturated (Bio)isosteres of Benzene Rings

AbstractRecently, many saturated bioisosteres of the benzene ring have been developed, and their applications in drug development have been evaluated. Most of these bioisosteres are caged hydrocarbons, which have rigid skeletons and three-dimensional spaces. Recent efforts to synthesize these caged hydrocarbons have enabled access to multi-functionalized congeners that are expected to be (bio)isosteres of multi-functionalized benzenes. This short review summarizes recently reported methods for obtaining multi-functionalized (typically more than disubstituted) caged hydrocarbons.1 Introduction2 Proposed Structures of Caged Hydrocarbons as Saturated (Bio)isosteres of the Benzene Ring: A Brief Summary3 Access to Multi-functionalized Caged Hydrocarbons: De Novo Synthetic Approaches3.1 Bicyclo[1.1.1]pentanes (BCPs)3.2 Bicyclo[2.1.1]hexanes (BCHs)3.3 Bicyclo[3.1.1]heptanes (BCHeps)3.4 Others4 Access to Multi-functionalized Caged Hydrocarbons: C–H Functionalization5 Conclusion

Library‐Friendly Synthesis of Bicyclo[1.1.1]pentane‐Containing Sulfonamides via a Transition Metal‐Free Three‐Component Reaction

AbstractHerein we report the synthesis of bicyclo[1.1.1]pentane (BCP)‐containing sulfonamides via a transition metal‐free process of a three‐component reaction among BCP‐containing N‐tosyl hydrazones, 1,4‐diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO), and amines. Different from existing methods to synthesize BCP‐containing sulfonamides, our method avoids the usage of sulfonyl halides, which could be challenging due to chemical instabilities. We have also demonstrated that this methodology is suitable for library synthesis of such sulfonamides. As a result, we can expect future application in drug discovery.

Difluorocarbene Enables Modular Synthesis of Difluoroalkylated Bicyclopentanes

A straightforward method for the synthesis of difluoroalkylated bicyclopentanes (BCPs) from [1.1.1]propellane (TCP) through a stepwise procedure has been developed. This process involves nucleophilic addition of organozinc or ArMgBr rea‐gents to TCP, followed by reaction with difluorocarbene to generate BCP substituted difluoroalkylzinc species, which subsequently couple with electrophiles, including allyl/propargyl bromides, (hetero)aryl disulfides, and proton, to provide a wide range of difluoroalkylated BCPs that otherwise are difficult to access through conventional methods. The transformations of the resulting products demonstrate the synthetic utility of this modular synthesis.

Synthesis of Azo-Substituted Bicyclo[1.1.1]pentanes (BCPs) via Base-Promoted Halogen Atom Transfer.

Because of the three-dimensional bioisosteric feature, bicyclo[1.1.1]pentylamines (BCPAs) are valuable scaffolds in synthetic chemistry and medicinal chemistry. Here, we report a Halogen Atom Transfer (XAT) mediated radical C-N coupling between C3-iodo-BCPs and diazonium salts in the presence of base. Similarly, a multicomponent reaction (MCR) enables the simultaneous construction of the C-C bond and C-N bond simultaneously. Versatile roles of diazonium salts were also explored.

Enantioselective Synthesis of α-Chiral Bicyclo[1.1.1]pentanes via Multicomponent Asymmetric Allylic Alkylation.

Bicyclo[1.1.1]pentanes (BCPs) have emerged as important structural motifs in drug design. However, asymmetric transformations that provide chiral BCPs bearing an adjacent stereocenter are still scarce. Here, we report a catalytic methodology for the enantioselective synthesis of α-chiral 1,3-difunctionalized BCPs from a three-component coupling of [1.1.1]propellane, a Grignard reagent, and an allylic phosphate. The reaction proceeds via the addition of the Grignard reagent to [1.1.1]propellane followed by an asymmetric N-heterocyclic carbene (NHC)-catalyzed allylic substitution of the resulting BCP-Grignard, providing a broad range of α-chiral BCPs with excellent levels of regioselectivity and enantioselectivity.

Synthesis of a Bicyclo[1.1.1]pentane‐Containing Aromatic Lipoxin B4 Analogue and Heteroaromatic Congeners

AbstractLipoxins are pro‐resolving mediators that play an important role in the resolution phase of the innate inflammatory response. However, because of their chemical and metabolic instability, the design of more stable synthetic analogues of lipoxin A4 and lipoxin B4 is an ongoing area of study. Herein we report the asymmetric synthesis of an aromatic lipoxin B4 analogue containing a conformationally rigid and potentially more metabolically resistant bicyclo[1.1.1]pentane (BCP) ring incorporated into the upper alkyl chain. This was achieved by the development of a 9‐step chiral‐pool synthesis of a novel BCP‐containing boronic ester coupling partner which could serve as a common precursor to the target analogue as well as other analogues with further modifications to the aromatic core.

Photoinduced C(sp3)‐H Bicyclopentylation Enabled by an Electron Donor–Acceptor Complex‐Mediated Chemoselective Three‐Component Radical Relay

The photoredox electron donor–acceptor (EDA) complex‐mediated radical coupling reaction has gained prominence in the field of organic synthesis, finding widespread application in two‐component coupling reactions. However, EDA complex‐promoted multi‐component reactions are not well developed with only a limited number of examples have been reported. Herein, we report a photoinduced and EDA complex‐promoted highly chemoselective three‐component radical arylalkylation of [1.1.1]propellane, which allows the direct functionalization of C(sp3)–H with bicyclo[1.1.1]pentanes (BCP)‐aryl groups under mild conditions. A variety of unnatural α‐amino acids, featuring structurally diversified 1,3‐disubstituted BCP moieties, were synthesized in a single‐step process. Notably, leveraging the high tension release of [1.1.1]propellane, the highly unstable transient aryl radical undergoes rapid conversion into a relatively stable tertiary alkyl transient radical, and consequently, the competing side‐reaction of two‐component coupling was entirely suppressed. The strategic use of this transient radical conversion approach would be useful for the design of diverse EDA complex‐mediated multi‐component reactions. It is noteworthy that the highly chemoselective late‐stage incorporation of the 1,3‐disubstituted BCP pharmacophores into peptides was achieved both in liquid‐phase and solid‐phase reactions. This advancement is anticipated to have significant application potential in the future development of peptide drugs.

Iodosulfonylation of [1.1.1]Propellane

AbstractAn efficient disubstituted functionalization of [1.1.1]propellane has been developed. The protocol utilizes sulfonyl hydrazides and N-iodosuccinimide, enabling the introduction of iodine and sulfonyl groups into bicyclo[1.1.1]pentane (BCP) in moderate to excellent yields. It has the advantages of simple operation, mild conditions, and broad substrate scope.

Reaction Paradigms that Leverage Cycloaddition and Ring Strain to Construction Bicyclic Aryl Bioisosteres from Bicyclo[1.1.0]butanes

AbstractWithin a medicinal chemist's toolbox, one of the most effective strategies to improve the overall properties of a biologically active compound is bioisosteric replacement. Ever since the first example of replacing benzene with a bicyclo[1.1.1]pentane (BCP) group was published in the late 1990s,[1] the medicinal chemistry community has continually been expanding the scope of such phenyl bioisosteric replacements. Recent interest from academia has focused on novel synthetic strategies to access C(sp3)‐rich bicyclic hydrocarbons with expanded ring sizes. Herein, we summarize some of these transformations and reveal that most rely on strain releasing cycloadditions with bicyclo[1.1.0]butane (BCB) and bicyclo[2.1.0]pentane (housane). We have organized this review based on the mechanism of such strain release strategies, namely, carbene cycloadditions, energy transfer photocatalyzed cycloadditions, electron transfer catalyzed cycloadditions, and polar cycloadditions.