Vicinal diamino functionalities as privileged structural elements in biologically active compounds and exploitation of their synthetic chemistry

Guanidine-Amide-Catalyzed Aza-Henry Reaction of Isatin-Derived Ketimines: Origin of Selectivity and New Catalyst Design

Density functional theory (DFT) calculations were performed to investigate the mechanism and the enantioselectivity of the aza-Henry reaction of isatin-derived ketimine catalyzed by chiral guanidine–amide catalysts at the M06-2X-D3/6-311+G(d,p)//M06-2X-D3/6-31G(d,p) (toluene, SMD) theoretical level. The catalytic reaction occurred via a three-step mechanism: (i) the deprotonation of nitromethane by a chiral guanidine–amide catalyst; (ii) formation of C–C bonds; (iii) H-transfer from guanidine to ketimine, accompanied with the regeneration of the catalyst. A dual activation model was proposed, in which the protonated guanidine activated the nitronate, and the amide moiety simultaneously interacted with the ketimine substrate by intermolecular hydrogen bonding. The repulsion of CPh₃ group in guanidine as well as N-Boc group in ketimine raised the Pauli repulsion energy (∆E_Pauli) and the strain energy (∆E_strain) of reacting species in the unfavorable si-face pathway, contributing to a high level of stereoselectivity. A new catalyst with cyclopropenimine and 1,2-diphenylethylcarbamoyl as well as sulfonamide substituent was designed. The strong basicity of cyclopropenimine moiety accelerated the activation of CH₃NO₂ by decreasing the energy barrier in the deprotonation step. The repulsion between the N-Boc group in ketimine and cyclohexyl group as well as chiral backbone in the new catalyst raised the energy barrier in C–C bond formation along the si-face attack pathway, leading to the formation of R-configuration product. A possible synthetic route for the new catalyst is also suggested.

Photoredox-Catalyzed Decarboxylative Cross-Coupling of α-Amino Acids with Nitrones

A decarboxylative cross-coupling reaction of α-amino acids with nitrones via visible-light-induced photoredox catalysis has been established for easy access to β-amino hydroxylamines and vicinal diamines with structural diversity, which is featured with simple operation, mild conditions, readily available α-amino acids, and a broad scope of nitrone substrates. The application of this protocol can furnish efficient synthetic strategies for some valuable vicinal diamine-containing molecules.

Highly diastereoselective synthesis of vicinal diamines via a Rh-catalyzed three-component reaction of diazo compounds with diarylmethanimines and ketimines

A Rh-catalyzed selective three-component reaction of diazo compounds with diarylmethanimines and ketimines is reported that offers an efficient and convenient access to vicinal diamine derivatives with two tertiary stereocenters in high yields.

Dirhodium(ii)-catalyzed diamination reaction via a free radical pathway

Unlike C–N bond formation through the well-known dirhodium(ii)-nitrenoid pathway, dirhodium(ii)-catalyzed 1,2- and 1,3-diamination reactions are realized by a free radical mechanism.

Vicinal difunctionalization of carbon-carbon double bond for the platform synthesis of trifluoroalkyl amines

Regioselective vicinal diamination of carbon-carbon double bonds with two different amines is a synthetic challenge under transition metal-free conditions, especially for the synthesis of trifluoromethylated amines. However, the synthesis of ethylene diamines and fluorinated amine compounds is demanded, especially in the pharmaceutical sector. Herein, we demonstrate that the controllable double nucleophilic functionalization of an activated alkene synthon, originated from a trifluoropropenyliodonium salt with two distinct nucleophiles, enables the selective synthesis of trifluoromethylated ethylene amines and diamines on broad scale with high efficiency under mild reaction conditions. Considering the chemical nature of the reactants, our synthetic approach brings forth an efficient methodology and provides versatile access to highly fluorinated amines.

Synthesis of chiral anti-1,2-diamine derivatives through copper(I)-catalyzed asymmetric α-addition of ketimines to aldimines

Chiral 1,2-diamines serve as not only common structure units in bioactive molecules but also useful ligands for a range of catalytic asymmetric reactions. Here, we report a method to access anti-1,2-diamine derivatives. By means of the electron-withdrawing nature of 2- or 4-nitro-phenyl group, a copper(I)-catalyzed asymmetric α-addition of ketimines derived from trifluoroacetophenone and 2- or 4-NO₂-benzylamines to aldimines is achieved, which affords a series of chiral anti-1,2-diamine derivatives in moderate to high yields with moderate to high diastereoselectivity and high to excellent enantioselectivity. Aromatic aldimines, heteroaromatic aldimines, and aliphatic aldimines serve as suitable substrates. The nitro group is demonstrated as a synthetical handle by several transformations, including a particularly interesting Fe(acac)₃-catalyzed radical hydroamination with a trisubstituted olefin. Moreover, the aryl amine moiety obtained by the reduction of the nitro group serves as a synthetically versatile group, which leads to the generation of several functional groups by the powerful Sandmeyer reaction, such as -OH, -Br, -CF₃, and -BPin.

Chiral 1,2-diamines are useful chemicals used as ligands in asymmetric catalysis. Here, the authors report a copper(I)-catalyzed asymmetric α-addition of ketimines derived from trifluoroacetophenone and 2- or 4-NO2-benzylamines to aldimines, affording a series of chiral anti-1,2-diamine derivatives.

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

A simple photocatalytic method was developed for the synthesis of unsymmetrical 1,2-diamines by the unprecedented reductive coupling of N-benzylidene-[1,1'-biphenyl]-2-amines with an aliphatic amine. The presence of a phenyl substituent in the aniline moiety of the substrate was critical for the reactivity. The reaction proceeded via radical–radical cross-coupling of α-amino radicals generated by proton-coupled single-electron transfer in the presence of an Ir photocatalyst. On the other hand, symmetrical 1,2-diamines were selectively produced from the same starting materials by the judicious choice of the reaction conditions, showcasing the distinct reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines. The developed method can be employed for the synthesis of various bulky vicinal diamines, which are potential ligands in stereoselective synthesis.

Catalytic Lewis and Brønsted acid syn-diastereoselective benzylic substitutions of α-hydroxy-β-nitro- and α-hydroxy-β-azido-alkyl arenes

A series of alkyl and alkenyl p-methoxy arenes containing α,β-disubstituted diamino and amino alcohol groups were synthesized from β-nitro and β-azido benzylic alcohols in the presence of AuCl3 as catalyst. The formation of predominantly syn-disubstituted products were rationalized on the basis of mechanistic considerations and transition state models relying on A1,3-allylic strain. The products could have utility in the design of medicinally relevant compounds and as chiral ligands for asymmetric catalysis. A new synthesis of (+)-sertraline (Zoloft) was achieved.

Rhodium(III)-Catalyzed Three-Component 1,2-Diamination of Unactivated Terminal Alkenes

We report a three-component diamination of simple unactivated alkenes using an electrophilic nitrene source and amine nucleophiles. The reaction provides rapid access to 1,2-vicinal diamines from terminal alkenes through a one-pot protocol. The transformation proceeds smoothly with excellent tolerance for a broad array of primary and secondary amines, affording the desired product with good yield and regioselectivity. The mechanism is proposed to proceed through a Rh(III)-catalyzed aziridination of alkenes with subsequent ring opening by primary or secondary amines.

Rhodium(iii)-catalyzed diamidation of olefins via amidorhodation and further amidation

Rh(iii)/Co(iii)-catalyzed diamidation of amide-tethered olefins has been realized using dioxazolones and arylsulfonamides as different classes of amidating reagents.

Cu(ii) salen and 1,2,4-triazole complexes from thiosemicarbazone: synthesis, physicochemical and structural properties and cytotoxic activities

The complexes were synthesized from reaction of salicylaldehydethiosemicarbazone and ethylenediamine in the presence of CuCl₂.

2-Unsubstituted Imidazole N-Oxides as Novel Precursors of Chiral 3-Alkoxyimidazol-2-ylidenes Derived from trans-1,2-Diaminocyclohexane and Other Chiral Amino Compounds

‘Desymmetrization’ of trans-1,2-diaminocyclohexane by treatment with α,ω-dihalogenated alkylation reagents leads to mono-NH₂ derivatives (‘primary-tertiary diamines’). Upon reaction with formaldehyde, these products formed monomeric formaldimines. Subsequently, reactions of the formaldimines with α-hydroxyiminoketones led to the corresponding 2-unsubstituted imidazole N-oxide derivatives, which were used here as new substrates for the in situ generation of chiral imidazol-2-ylidenes. Upon O-selective benzylation, new chiral imidazolium salts were obtained, which were deprotonated by treatment with triethylamine in the presence of elemental sulfur. Under these conditions, the intermediate imidazol-2-ylidenes were trapped by elemental sulfur, yielding the corresponding chiral non-enolizable imidazole-2-thiones in good yields. Analogous reaction sequences, starting with imidazole N-oxides derived from enantiopure primary amines, amino alcohols, and amino acids, leading to the corresponding 3-alkoxyimidazole-2-thiones were also studied.

New cinnamic acid-pregenolone hybrids as potential antiproliferative agents: Design, synthesis and biological evaluation

A series of new cinnamic acid-pregenolone hybrids (5a-5o) was designed, synthesized and evaluated for their in vitro antiproliferative activity. Some of them showed potential antiproliferative activity and selectivity towards a panel of cancer cell lines, including A549, H157, HepG2, MCF-7, and HL-60. Among these analogs, compound 5f showed the most promising activity with IC₅₀ values ranging from 3.2 to 6.8 μM, and it was taken as a model compound in the following antiproliferative mechanism study. In Hoechst 33258 staining assay, 5f-treated A549 cells displayed significant apoptosis characteristics. Flow cytometry analysis revealed that 5f showed the antiproliferative activity against A549 via G1 cell cycle arrest and inducing apoptosis. Western blotting analysis demonstrated that 5f enhanced apoptosis of A549 cells by down-regulating Bcl-2 and up-regulating Bax protein expression. The present study highlighted this series of cinnamic acid-pregenolone hybrids as a new antiproliferative lead prototype.

Stereoselective Addition of a Lithium Anion of 1,1-Diphenyl-2-aza-pentadiene to Sulfinimines: Application to the Synthesis of (-)-Epiquinamide

The addition of a lithium anion of diphenylallylimine to nonracemic sulfinimines was investigated. It was found that the reaction with sulfinimines derived from aliphatic aldehydes afforded the products with excellent diastereoselectivity (>99:1), furnishing the product vicinal diamines in very good yields. Application of the formed product vicinal diamines was demonstrated in the total synthesis of the natural product (-)-epiquinamide.

2-Azadienes as Enamine Umpolung Synthons for the Preparation of Chiral Amines

The development of new strategies for the preparation of chiral amines is an important objective in organic synthesis. In this Synpacts, we summarize our approach for catalytically accessing nucleophilic aminoalkyl metal species from 2-azadienes, and its application in generating a number of important but elusive chiral amine scaffolds. Reductive couplings with ketones and imines afford 1,2-amino tertiary alcohols and 1,2-diamines, respectively, whereas fluoroarylations of gem-difluoro-2-azadienes deliver α-trifluoromethylated benzylic amines.

Regio- and Enantioselective Formal Hydroamination of Enamines for the Synthesis of 1,2-Diamines

The asymmetric formal hydroamination of enamines using a CuH catalyst is reported. The method provides a straightforward and efficient approach to the synthesis of chiral 1,2-dialkyl amines in good yields with high levels of enantioselectivities for a broad range of substrates, and should have significant value for the preparation of molecules bearing a 1,2-diamine motif.

Iodine-promoted Intermolecular Dehydrogenation Diamination: Synthesis of Unsymmetrical α,β-Diamido Ketones

Iodine-promoted direct diamination of α,β-unsaturated ketone to form two C-N bonds has been developed starting from chalcone and secondary amine. This reaction was performed in THF at 50 °C in the presence of I₂ and K₂ CO_3. The protocol is metal-free, operationally simple and carried out under mild conditions, providing an effective new way for directing diamination reactions.

Three-Step Telescoped Synthesis of Monosubstituted Vicinal Diamines from Aldehydes

Aldehydes are easily transformed into vicinal diamines and piperazines through a one-pot procedure including a Darzens reaction and treatment with an amine or diamine and then with a reducing agent. Additionally, quinoxalines can be accessed by reaction with 1,2-benzenediamine under oxidative conditions. These transformations are simple methods for the preparation of synthetically interesting monosubstituted diamines, piperazines, and quinoxalines.

Highly efficient biocatalytic desymmetrization of meso carbocyclic 1,3-dicarboxamides: a versatile route for enantiopure 1,3-disubstituted cyclohexanes and cyclopentanes

Highly efficient biocatalytic desymmetrization of meso carbocyclic 1,3-dicarboxamides to enantiopure 1,3-disubstituted cyclohexanes and cyclopentanes was realized.

Enantioselective Organocatalytic Amine-Isocyanate Capture-Cyclization: Regioselective Alkene Iodoamination for the Synthesis of Chiral Cyclic Ureas

Ureas of chiral diamines are prominent features of therapeutics, chiral auxiliaries, and intermediates in complex molecule synthesis. Although many methods for diamine synthesis are available, metal-free enantioselective alkene functionalizations to make protected 1,2- and 1,3-diamines from simple achiral starting materials are rare, and a single reagent that accesses a cross-section of each congener with high enantiomeric excess is not available. We describe a method to synthesize enantioenriched cyclic 5- and 6-membered ureas from allylic amines and an isocyanate using a C2-symmetric BisAmidine (BAM) catalyst that delivers N-selectivity from an ambident sulfonyl imide intermediate, overcoming electronic and steric deactivation at nitrogen. The geometry of 1,2-disubstituted alkenes is correlated to 5-exo and 6-endo cyclizations without altering alkene face selectivity, which is unexpectedly opposite that observed with O-nucleophiles. Straightforward product manipulations to diamine and imidazolidinone derivatives are underscored by the synthesis of an NK1 antagonist.

Aminative Umpolung cyclization for synthesis of chiral exocyclic vicinal diamines

Chiral exocylic vicinal diamines are biologically and chemically important compounds, but they are not easy to make. In this paper, an interesting aminative Umpolung cyclization process has been developed. Aromatic aldehydes 6 bearing an electrophilic chiral sulfinimine group underwent imine formation with 2,2-diphenylglycine (2), decarboxylation, and subsequent Umpolung cyclization, producing various trans-diamines 10 in 84-96% yields with high trans/cis ratios under very mild conditions. This work not only provides an efficient, clean, and mild method for the synthesis of chiral exocyclic vicinal diamines in one step but also represents a new application of aminative Umpolung strategy on intramolecular reactions.

Umpolung Synthesis of Vicinal Diamines: Diastereoselective Addition of 2-Azaallyl Anions to Davis-Ellman's Imines

A highly regioselective and diastereoselective addition of 2-azaallyl anions to N- tert-butanesulfinylimines is reported. This methodology affords the preparation of enantiomerically and diastereomerically pure vicinal diamines bearing two adjacent stereocenters. Reactions proceed efficiently (yield up to 94%), diastereoselectively ( dr values up to 98:2:0:0), and site-selectively to deliver products with differentiated amino groups.

Direct dihalo-alkoxylation of nitroalkenes leading to β,β-dihalo-β-nitroethyl alkyl ethers

A highly efficient one-pot synthesis of β,β-dihalo-β-nitroethyl alkyl ethers is achieved by the treatment of nitroalkenes with alcohols and N-halosuccinimides in the presence of sodium hydride. The notable advantages of this protocol are that it involves simple experimental manipulations and tolerates a wide range of functional groups. Further transformations of the obtained ethers, such as allylation and conversion to β,β-dihalogenated vinyl ethers, are also investigated.