Natural Occurrence, Syntheses, and Applications of Cyclopropyl-Group-Containing α-Amino Acids. 2. 3,4- and 4,5-Methanoamino Acids

Base-promoted highly efficient synthesis of nitrile-substituted cyclopropanes via Michael-initiated ring closure

A convenient and efficient annulation reaction has been developed for the general synthesis of dinitrile-substituted cyclopropanes in moderate to excellent yields. A variety of 2-arylacetonitriles and α-bromoennitriles were compatible under the standard conditions. The reaction was achieved through tandem Michael-type addition followed by intramolecular cyclization. The preliminary application of this method was confirmed by the synthesis of the 2,4-dioxo-3-azabicyclo[3.1.0]hexane scaffold.

Antiviral Cyclopropane Acids from Deep-Sea-Derived Fungus Aspergillus sydowii

Four novel monocyclic cyclopropane acids, namely, sydocyclopropanes A–D (1–4), along with one known congener hamavellone B (5), were isolated from the Aspergillus sydowii MCCC 3A00324 fungus, which was isolated from the deep-sea sediment. The gross structures of novel compounds were established by detailed analyses of the spectroscopic data (HRESIMS and NMR spectra), and their absolute configurations were resolved on the basis of the quantum chemical calculations of ECD and NMR data, in association with DP4+ probability analyses. Sydocyclopropanes A–D, featuring the 1,1,2,3-tetrasubstituted cyclopropane nucleus with different lengthy alkyl side chains, were discovered in nature for the first time. All compounds exhibited antiviral activities against A/WSN/33 (H1N1), with IC₅₀ values ranging from 26.7 to 77.2 μM, of which compound 1 exhibited a moderate inhibitory effect (IC₅₀ = 26.7 μM).

Developments in the Catalytic Asymmetric Synthesis of Agrochemicals and Their Synthetic Importance

Catalytic asymmetric synthesis has become an essential tool for the enantioselective synthesis of pharmaceuticals, natural products, and agrochemicals (mainly fungicides, herbicides, insecticides, and pheromones). With continuous growing interest in both modern agricultural chemistry and catalytic asymmetric synthesis chemistry, this review provides a comprehensive overview of some earlier reports as well as the recent successful applications of various catalytic asymmetric syntheses methodologies, such as enantioselective hydroformylation, enantioselective hydrogenation, asymmetric Sharpless epoxidation and dihydroxylation, asymmetric cyclopropanation or isomerization, organocatalyzed asymmetric synthesis, and so forth, which have been used as key steps in the preparation of chiral agrochemicals (on R&D, piloting, and commercial scales). Chiral agrochemicals can also lead the new generation of such chemicals having specific and novel modes of action for achieving sustainable crop protection and production. Some perspectives and challenges for these catalytic asymmetric methodologies in the synthesis of chiral agrochemicals are also briefly discussed in the final section of the manuscript. This review will provide the insight regarding understanding, development, and evaluation of catalytic asymmetric systems for the synthesis of chiral agrochemicals among the agrochemists.

Biosynthesis of cyclopropane in natural products

Covering: 2012 to 2021Cyclopropane attracts wide interests in the fields of synthetic and pharmaceutical chemistry, and chemical biology because of its unique structural and chemical properties. This structural motif is widespread in natural products, and is usually essential for biological activities. Nature has evolved diverse strategies to access this structural motif, and increasing knowledge of the enzymes forming cyclopropane (i.e., cyclopropanases) has been revealed over the last two decades. Here, the scientific literature from the last two decades relating to cyclopropane biosynthesis is summarized, and the enzymatic cyclopropanations, according to reaction mechanism, which can be grouped into two major pathways according to whether the reaction involves an exogenous C1 unit from S-adenosylmethionine (SAM) or not, is discussed. The reactions can further be classified based on the key intermediates required prior to cyclopropane formation, which can be carbocations, carbanions, or carbon radicals. Besides the general biosynthetic pathways of the cyclopropane-containing natural products, particular emphasis is placed on the mechanism and engineering of the enzymes required for forming this unique structure motif.

Functionalized Cyclopropanes as Versatile Intermediates for the Diversity-Oriented Synthesis of γ-Lactones, γ-Lactams and δ-Lactams

A two-step procedure for the preparation of cyclopropanecarboxaldehyde-1,1-diester from a γ,δ-epoxyester and its synthetic versatility are described herein. The epoxide ring-opening/cyclopropanation process occurs in the presence of Mg(ClO4)2 under heating, resulting in cyclopropanemethanol-1,1-diester in 65% yield. A mild TEMPO-mediated oxidation of this substrate readily generated the corresponding aldehyde in 75% yield, which was applied in the one-pot synthesis of four cyclopropylidene-γ-lactams and three δ-lactams. In addition, vinylcyclopropanes were obtained through the Wittig reaction of the aldehyde with phosphonium salts and used as precursors for tetrahydrofurans.

Palladium-Catalyzed Amination/Dearomatization Reaction of Indoles and Benzofurans

This report describes a palladium-catalyzed dearomatization and amination tandem reaction of 2,3-disubstituted indoles and benzofurans via the Catellani strategy. This reaction provides a new method for the construction of amino-substituted indoline-fused cyclic and benzofuran spiro compounds in good yields. The reaction has broad functional group compatibility and substrate scope.

Enantioselective construction of dispirotriheterocycles featuring a 4-aminopyrazolone motif through a cascade Michael/cyclization process

A highly asymmetric approach to multicyclic dispiro [pyrazolone-pyrrolidinethione-oxindole] core structures bearing three contiguous stereogenic centers through a cascade Michael addition/cyclization reaction of 4-isothiocyanato pyrazolones with 3-ylideneoxindoles was developed.

Efficient trifluoromethylation via the cyclopropanation of allenes and subsequent C–C bond cleavage

Trifluoromethyl has been efficiently incorporated into organic skeletons via allene cyclization and C–C bond cleavage.

Cascade assembling of pyrazolin-5-ones and benzylidenemalononitriles: the facile and efficient approach to medicinally relevant spirocyclopropylpyrazolone scaffold

A new cascade reaction provides a direct transformation of pyrazolin-5-ones and benzylidene-malononitriles by the action of bromine into substituted spirocyclopropylpyrazolones in 60–88% yields. This process can be realized in two variants, namely, (1) by treatment with bromine in the presence of base and (2) by treatment with bromine only with heating. These facile and efficient one-step cascade processes lead to the spirocyclopropylpyrazolone framework, which is present in a perspective class of compounds with prominent pharmacological and physiological activity.

Electrocatalytic stereoselective transformation of aldehydes and two molecules of pyrazolin-5-one into (R*,R*)-bis(spiro-2,4-dihydro-3H-pyrazol-3-one)cyclopropanes

The electrocatalytic transformation of aldehydes and pyrazolin-5-one stereoselectively leads to (R*,R*)-bis(spiro-2,4-dihydro-3H-pyrazol-3-one)cyclopropanes in 65–80% yields.

symm-Tetramethylenecyclooctane: en route to polyspirocycles

A straightforward gram-scale synthesis of 1,3,5,7-tetrakis(methylidene)cyclooctane (TMCO) from commercial adamantane-1,3-dicarboxylic acid has been developed. TMCO exhibits high reactivity toward a number of carbenes and epoxidizing reagents, undergoing multiple cyclopropanations, dihalocyclopropanations, or epoxidations of four double bonds to yield polyspirocyclic products. Stereochemical features of polyspirocyclopropanated compounds have been thoroughly examined in experimental (NMR) and theoretical (DFT) studies. Comprehensive stereochemical assignment of TMCO adducts with dihalocarbenes and spiroepoxy products was achieved. The conditions of the formation of 1-methyl-3,7-bis(methylidene)bicyclo[3.3.1]nonane from the adamantane derivative were optimized, and diadducts of this diene with dihalocarbenes were isolated and characterized.

Cyclization and annulation reactions of nitrogen-substituted cyclopropanes and cyclobutanes

This feature article covers recent progress in cyclization and annulation reactions of aminocyclopropanes and aminocyclobutanes to access nitrogen-rich building blocks.

Concise Synthesis of Enantiomerically Pure (1'S,2'R)- and (1'R,2'S)-2S-Amino-3-(2'-aminomethyl-cyclopropyl)propionic Acid: Two E-Diastereoisomers of 4,5-Methano-L-lysine

A concise synthesis of both E-isomers of 2S-amino-3-(2′-aminomethyl-cyclopropyl)propionic acid, new methano-l-lysines, is described. The synthetic route includes nine steps from l-methionine, with a key step involving the cyclopropanation of an intermediate E-allylic alcohol. The resultant hydroxymethylcyclopropanes were readily separated and converted into the title α-amino acids. The stereochemistry around the cyclopropane rings was deduced by conducting the cyclopropanation in the presence of N,N,N′,N′-tetramethyl-d-tartaric acid diamide butylboronate, a chiral controller which is known to favour the production of S-hydroxymethyl cyclopropanes from allylic alcohols.

Gold(I)-catalysed cycloisomerisation of 1,6-cyclopropene-enes

The gold(I)-catalysed cycloisomerisation of appropriately substituted 1,6-cyclopropene-enes proceeds through regioselective electrophilic ring opening of the three-membered ring to generate an alkenyl gold carbenoid that achieves the intramolecular cyclopropanation of the remote olefin. This strategy allows straightforward, highly efficient and diastereoselective access to a variety of substituted 3-oxa- and 3-azabicyclo[4.1.0]heptanes, as well as to bicyclo[4.1.0]heptan-3-ol derivatives. Since the isopropylidene group in the resulting cycloisomerisation products can be subjected to ozonolysis, 3,3-dimethylcyclopropenes behave as interesting surrogates for α-diazoketones.