Catalytic Conversion of Diazocarbonyl Compounds to Imines: Applications to the Synthesis of Tetrahydropyrimidines and β-Lactams

Csp3-H Imination Using Arylazo Sulfone as a N Source: An Approach to Access Imines

An unprecedented Csp3-H imination reaction using arylazo sulfones as the readily accessible and stable N source is reported. The synthetic virtues are demonstrated through mild conditions, simple operation, good air compatibility, and functional group tolerance, as well as suitability for gram-scale reaction. The resulting imines can be further converted to α-amino acids. The presented results shed light on an unusual usage of arylazo sulfones and will inspire novel experimental design by using arylazo sulfones as the N source.

Sc(OTf)3-Catalyzed [3+2]-Cycloaddition of Diazoacetoacetate Enones and N-Aryl Nitrones: Diastereoselective Synthesis of Functionalized Isoxazolidines with Three Contiguous Stereogenic Centers

A catalytic [3+2]-cycloaddition using Sc(OTf)3 as a Lewis acid catalyst is developed. This catalytic 1,3-dipolar cycloaddition dia­stereoselectively transforms diazoacetoacetate enones and N-aryl nitrones into highly functionalized isoxazolidines bearing three contiguous chiral centers. The feasibility of the uncatalyzed 1,3-dipolar cycloaddition is postulated by DFT calculations and substantiated experimentally.

Diastereoselective formation of β-lactams via a three-component reaction

A highly diastereoselective three-component reaction of N-hydroxyanilines, diazo compounds and cyclobutenones to form densely functionalized β-lactams has been realized.

Visible-Light-Mediated Strategies to Assemble Alkyl 2-Carboxylate-2,3,3-Trisubstituted β-Lactams and 5-Alkoxy-2,2,4-Trisubstituted Furan-3(2H)-ones Using Aryldiazoacetates and Aryldiazoketones

Two new visible-light-mediated strategies are described starting from aryldiazoacetates. The first approach describes their reaction with azides to afford the corresponding imines, and then reaction with aryldiazoketones produces alkyl 2-carboxylate-2,3,3-trisubstituted β-lactams. The second approach describes the reaction with sulfoxides to afford the corresponding sulfoxonium ylides, followed by reaction with aryldiazoketones to produce 5-alkoxy-2,2,4-trisubstituted furan-3(2H)-ones. These protocols take advantage of the photolysis of aryldiazoacetates and the photochemically promoted Wolff rearrangement of aryldiazoketones.

Synthesis of β- and γ-lactam fused dihydropyrazinones from Ugi adducts via a sequential ring construction strategy

A modular approach for the construction of β- and γ-lactam fused dihydropyrazinones from the readily available Ugi adducts has been described. The sequential construction of rings through base-mediated cycloisomerization followed by acid-mediated cyclization yielded β-lactam fused dihydropyrazinones. However, the Ugi-derived dihydropyrazinones afforded γ-lactam fused dihydropyrazinones under base-mediated cycloisomerization. The regioselectivity in the cycloisomerization reactions is explained on the basis of ring-strain. Substrate scope, limitations and mechanistic investigations through DFT-calculations have been explored.

Azetidin-2-ones: structures of anti-mitotic compounds based on the 1-(3,4,5-tri-meth-oxy-phen-yl)azetidin-2-one core

A series of related substituted 1-(3,4,5-tri-meth-oxy-phen-yl)azetidin-2-ones have been characterized: 3-(4-fluoro-phen-yl)-4-(4-meth-oxy-phen-yl)-1-(3,4,5-tri-meth-oxy-phen-yl)azetidin-2-one, C25H24FNO5 (1), 3-(furan-2-yl)-4-(4-meth-oxy-phen-yl)-1-(3,4,5-tri-meth-oxy-phen-yl)azetidin-2-one, C23H23NO6 (2), 4-(4-meth-oxyphen-yl)-3-(naphthalen-1-yl)-1-(3,4,5-tri-meth-oxy-phen-yl)azetidin-2-one, C29H27NO5 (3), 3-(3,4-di-meth-oxy-phen-yl)-4-(4-meth-oxy-phen-yl)-1-(3,4,5-tri-meth-oxy-phen-yl)azetidin-2-one, C27H29NO7 (4) and 4,4-bis-(4-meth-oxy-phen-yl)-3-phenyl-1-(3,4,5-tri-meth-oxy-phen-yl)azetidin-2-one, C32H31NO6 (5). All of the compounds are racemic. The lactam and 3,4,5-tri-meth-oxy-phenyl rings are approximately co-planar and the orientation of the lactam and the 4-meth-oxy-phenyl substituent is approximately orthogonal. The chiral centres, although eclipsed by geometry, have torsion angles ranging from -7.27 to 13.08° for the 3 position, and -8.69 to 13.76° for the 4 position of the β-lactam. The structures display intra-molecular C-H⋯O bonding between the 3,4,5-tri-meth-oxy-phenyl ring and the lactam ketone. Further C-H⋯O inter-actions are observed and form either an opposing meth-oxy 'buckle' to join two mol-ecules together or a cyclic dimer.

Synthesis of biologically relevant steroidal spiro β-lactams from dienamides through the cascade 4-endo N-cyclization/aerobic oxidation sequence

The steroid nucleus and β-lactam are prevalent in natural products and drug molecules, the compounds containing such fragments always possess diverse and interesting biological profiles. Presented here is an unprecedented cascade 4-endo N-cyclization/aerobic oxidation sequence that enables the synthesis of biologically relevant steroidal spiro β-lactams from dienamides. Of note, two continuous quaternary chiral centers were constructed simultaneously in this process, and the title compounds bearing the OH and CN groups are highly functionalized, allowing for late-stage transformations for construction of diverse compound library. The protocol has several advantages such as mild reaction conditions and short reaction time, therefore could serve as a new strategy for synthesizing β-lactams.

Synthesis of Chiral Tetrasubstituted Azetidines from Donor-Acceptor Azetines via Asymmetric Copper(I)-Catalyzed Imido-Ylide [3+1]-Cycloaddition with Metallo-Enolcarbenes

The all-cis stereoisomers of tetrasubstituted azetidine-2-carboxylic acids and derivatives that possess three chiral centers have been prepared in high yield and stereocontrol from silyl-protected Z-γ-substituted enoldiazoacetates and imido-sulfur ylides by asymmetric [3+1]-cycloaddition using chiral sabox copper(I) catalysis followed by Pd/C catalytic hydrogenation. Hydrogenation of the chiral p-methoxybenzyl azetine-2-carboxylates occurs with both hydrogen addition to the C=C bond and hydrogenolysis of the ester.

Direct α-Imination of N-Acyl Pyrazoles with Nitrosoarenes

Unprecedented α-imino N-acyl pyrazoles were efficiently and selectively prepared through the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed reaction of nitrosoarenes with N-acyl pyrazoles via an N-nitroso aldol reaction/dehydration sequence. The α-imino acyl pyrazoles were demonstrated to be new versatile intermediates for practical one-pot syntheses of α-imino amides, dipeptide precursors, esters, and β-amino alcohols. The synthetic method competes with known protocols in terms of ready availability of the reagents and catalyst, mild and catalytic reaction conditions, gram-scale applicability, and scope of the α-imino acid derivatives achievable.

Synthesis of Isoindoles from Intramolecular Condensation of Benzyl Azides with α-Aryldiazoesters

Rh-catalyzed intramolecular condensation of the benzyl azides with α-aryldiazoesters was explored. The reaction proceeded through the nucleophilic attack of the organic azide onto a rhodium carbenoid, while releasing nitrogen gas, affording the α-imino esters as the primary product. Tautomerization of the imino esters efficiently gave 13 desired isoindoles with good to excellent yields.

Catalyst-free synthesis of tetrahydropyrimidines via formal [3+3]-cycloaddition of imines with 1,3,5-hexahydro-1,3,5-triazines

A practical and environmentally benign synthesis of poly-substituted tetrahydropyrimidines from readily available starting materials has been developed. This process features an unprecedented intermolecular formal [3+3]-annulation of imines and 1,3,5-hexahydro-1,3,5-triazines under catalyst-free conditions. Importantly, differing from previous transformations, the 1,3,5-triazines are firstly utilized as formal 1,3-dipoles in cycloaddition reactions.

A practical and environmentally benign synthesis of poly-substituted tetrahydropyrimidines via formal [3+3]-annulation of imines and 1,3,5-hexahydro-1,3,5-triazines under catalyst-free conditions has been developed.

CN bond formation via palladium-catalyzed carbene insertion into NN bonds: inhibiting the general 1,2-migration process of ylide intermediates

Inhibiting the general 1,2-migration process of ylide intermediates, a new palladium-catalyzed carbene insertion into NN bonds affords various N,N-disubstituted hydrazones.

Asymmetric Intramolecular Desymmetrization of meso-α,α'-Diazido Alcohols with Aryldiazoacetates: Assembly of Chiral C3 Fragments with Three Continuous Stereocenters

The chiral Cu-complex-catalyzed intramolecular interception of meso-α,α'-diazido alcohols with aryldiazoacetates is explored. Most of the enantioenriched α-imino esters with three continuous stereocenters are produced with good to excellent yield and enantioselectivity, and a chiral pocket model is proposed for rationalization of the asymmetric desymmetrization.

Copper-catalyzed condensation of imines and α-diazo-β-dicarbonyl compounds: modular and regiocontrolled synthesis of multisubstituted pyrroles

The Cu-catalyzed condensation of ketimines and diazodicarbonyl compounds enables the rapid and regiocontrolled synthesis of pharmaceutically relevant multisubstituted pyrroles.

In the presence of a copper(ii) catalyst, enolizable imines bearing various N-substituents and α-diazo-β-ketoesters undergo denitrogenative and dehydrative condensation to afford highly substituted pyrroles in moderate to good yields with exclusive regioselectivity. The reaction likely involves nucleophilic addition of the imine nitrogen to a copper carbenoid, tautomerization of the resulting azomethine ylide to an α-enaminoketone, and a subsequent enamine–ketone cyclocondensation. With Yb(OTf)₃ as a unique cocatalyst, α-diazo-β-diketones also participate in the same condensation reaction. The present reaction is applicable to acyclic, exocyclic, and endocyclic imines with tolerance of a broad range of functional groups and heterocyclic moieties, thus opening a new convenient route for the synthesis of the lamellarin family of natural products.

Domino reactions of diazodicarbonyl compounds with α,β-unsaturated δ-amino esters: a convenient way towards 2-oxopiperidines, dihydropyridinones and isoquinolinediones

Thermal decomposition of a series of diazodicarbonyl compounds in the presence of α,β-unsaturated δ-amino esters and sodium hydride gives rise to a variety of nitrogenous heterocycles.

Azide trapping of metallocarbenes: generation of reactive C-acylimines and domino trapping with nucleophiles

Diazocarbonyl compounds react with pendent azides under copper catalysis to generate reactive C-acylimines that can be trapped with carbon π-nucleophiles in situ.