Donor-Acceptor Cyclopropane Ring Opening with 6-Amino-1,3-dimethyluracil and Its Use in Pyrimido[4,5-b]azepines Synthesis

Concise approach to γ-(het)aryl- and γ-alkenyl-γ-aminobutyric acids. Synthesis of vigabatrin

γ-Aminobutyric acid (GABA) and GABA derivatives have attracted increased attention over the years in the fields of medicinal chemistry and chemical biology due to their interesting biological properties and synthetic relevance. Here, we report a short synthetic route to γ-(het)aryl- and γ-alkenyl-γ-aminobutyric acids, including the antiepileptic drug vigabatrin, from readily available donor-acceptor cyclopropanes and ammonia or methylamine. This protocol includes a facile synthesis of 2-oxopyrrolidine-3-carboxamides and their acid hydrolysis to γ-aryl- or γ-alkenyl-substituted GABAs, which can serve as perspective building blocks for the synthesis of various GABA-based N-heterocycles and bioactive compounds.

Benzotriazole-Triggered Three-Component Lewis Acid-Catalyzed Ring-Opening 1,3-Aminofunctionalization of Donor-Acceptor Cyclopropanes

The use of benzotriazoles as nucleophilic triggers in the three-component Yb(OTf)₃-catalyzed ring-opening 1,3-aminofunctionalization of donor-acceptor (D-A) cyclopropanes is presented. Using N-halo succinimide (NXS) as the third component, the reaction afforded the 1,3-aminohalogenation product in up to an 84% yield. Moreover, using alkyl halides or Michael acceptors as the third components, the 3,1-carboaminated products are formed in up to a 96% yield in a one-pot operation. Employing Selectfluor as the electrophile, the reaction furnished the 1,3-aminofluorinated product in a 61% yield.

Synthesis of 1,5-Substituted Pyrrolidin-2-ones from Donor-Acceptor Cyclopropanes and Anilines/Benzylamines

We developed a straightforward synthetic route to pharmacologically important 1,5-substituted pyrrolidin-2-ones from donor-acceptor cyclopropanes bearing an ester group as one of the acceptor substituents. This method includes a Lewis acid-catalyzed opening of the donor-acceptor cyclopropane with primary amines (anilines, benzylamines, etc.) to γ-amino esters, followed by in situ lactamization and dealkoxycarbonylation. The reaction has a broad scope of applicability; a variety of substituted anilines, benzylamines, and other primary amines as well as a wide range of donor-acceptor cyclopropanes bearing (hetero)aromatic or alkenyl donor groups and various acceptor substituents can be involved in this transformation. In this process, donor-acceptor cyclopropanes react as 1,4-C,C-dielectrophiles, and amines react as 1,1-dinucleophiles. The resulting di- and trisubstituted pyrrolidin-2-ones can be also used in subsequent chemistry to obtain various nitrogen-containing polycyclic compounds of interest to medicinal chemistry and pharmacology, such as benz[g]indolizidine derivatives.

Ambident reactivity of 5-aminopyrazoles towards donor-acceptor cyclopropanes

Lewis acid-catalysed reactions of donor-acceptor cyclopropanes with 1,3-disubstituted 5-aminopyrazoles were investigated. Under catalysis with gallium(III) chloride, products of the three-membered ring opening via a nucleophilic attack of the exocyclic amino group were obtained in a chemoselective manner. Oppositely, in the presence of scandium(III) triflate, products of either N-alkylation or C(4)-alkylation, or a mixture of both were formed. The products of the C(4) alkylation were transformed in one step into tetrahydropyrazolo[3,4-b]azepines that are attractive for medicinal chemistry and pharmacology.

MgI2-Catalyzed Nucleophilic Ring-Opening Reactions of Donor-Acceptor Cyclopropanes with Indoline-2-thiones

MgI₂-catalyzed nucleophilic ring-opening reactions of donor-acceptor cyclopropanes with indoline-2-thiones as easy-to-handle sulfur nucleophiles were investigated. A series of functionalized γ-indolylthio butyric acid derivatives were synthesized in good to excellent yields under mild reaction conditions. Furthermore, the thioether functionalized ring-opening products could be transformed to sulfone and methionine analogues.

Expedient Ni(OTf)2/visible light photoredox-catalyzed annulation of donor-acceptor cyclopropanes with cyclic secondary amines

The annulative coupling of donor-acceptor cyclopropanes with cyclic secondary amines is reported using the combination of Ni(OTf)₂ and visible light assisted eosin Y catalysis for tandem C-N and C-C bond formation. The reaction sequence provides a potential synthetic tool for the construction of pyrrolotetrahydroisoquinolines.

Ring-Opening 1,3-Carbothiolation of Donor-Acceptor Cyclopropanes Using Alkyl Halides and In Situ Generated Dithiocarbamates

Two-step, ring-opening 1,3-carbothiolation of donor-acceptor (D-A) cyclopropanes employing alkyl halides and in situ generated dithiocarbamates (from amines and CS2) has been demonstrated under mild conditions. The reaction is operationally simple and works with good functional group compatibility. Three new bonds including C-N, C-S, and C-C are formed in this 1,3-bifunctionalization strategy. Electron-poor olefins can also be used as electrophiles instead of alkyl halides. The use of enantiomerically pure D-A cyclopropane afforded enantiopure 1,3-carbothiolated product, thus demonstrating the stereospecificity of the reaction.

Lewis acid triggered N-alkylation of sulfoximines through nucleophilic ring-opening of donor-acceptor cyclopropanes: synthesis of γ-sulfoximino malonic diesters

Scandium triflate (Sc(OTf)₃) catalyzed, mild, and regioselective ring-opening reaction of donor-acceptor (D-A) cyclopropanes has been developed using sulfoximines for the synthesis of γ-sulfoximino malonic diesters. This protocol allows the synthesis of different N-alkyl sulfoximines in good to excellent yields (up to 94%) with broad functional group tolerance. In this process, N-H and C-C bonds are cleaved to form new C-N and C-H bonds. The feasibility of this method is supported by a gram-scale reaction and synthetic elaboration of the obtained product.