Amidation of deltacyclene and hexacyclic norbornadiene dimers with acetonitrile and water catalyzed by FeCl3·6H2O

Abstract

FeCl₃·6H₂O-catalyzed Ritter amidation of deltacyclene and hexacyclic norbornadiene dimers containing both a double bond and a three-carbon ring in the molecule with acetonitrile and water was performed. Depending on the hydrocarbon structure, the reaction proceeds via C-C bond cleavage in the three-carbon ring or at the double bond to form the corresponding N-acetamides.     

Bonding Properties of Cyclopropane and Their Chemical Consequences

Among the cyclic compounds of carbon, cyclopropane and its derivatives are outstanding by virtue of their unusual structural, spectroscopic, and chemical properties. The cyclopropane ring more closely resembles the C?C double bond than the cyclobutane ring: it is a small ring with “double bond character”. Cyclopropyl and vinyl groups interact with neighbouring π-electron systems and p-electron centers; both cyclopropane derivatives and olefins form metal complexes, and add strong acids, halogens, and ozone; they both undergo catalytic hydrogenation and cycloadditions. While distinct differences in reactivity do exist–the double bond usually being more reactive than the three-membered ring–there are no fundamental differences in behavior.–Although cyclopropane derivatives have been known for more than 90 years, intensive studies have been limited to the past 25 years. The development of carbene chemistry has rendered cyclopropane derivatives far more readily accessible. In recent years, the synthetic potential of the small-ring function has been increasingly exploited. A considerable number of newly developed methods utilizing this approach clearly demonstrates that the reactivity of the cyclopropene ring, like that of the C?C double bond, qualify it as a “functional carbon group”. This development is in full swing; we may therefore justifiably devote considerable effort to the study of cyclopropane chemistry.     

The ab initio charge deformation density of bicyclobutane from an extended gaussian basis

The charge deformation density of bicyclobutane has been derived from SCF wavefunctions computed with two contracted gaussian bases, of double-zeta and double-zeta-plus-polarization quality. Carbon—carbon bond peaks are displaced to the outside of the three-carbon rings, the peak in the bridge bond being flatter and further from the CC line than those in the non-fused bonds. Inclusion of polarization functions broadens these peaks so that they merge in a flat plateau inside each cyclopropane triangle. The side bonds are also bent slightly out of the ring plane, evidently by non-bonded repulsion between the methylene carbon atoms. Partitioning into atomic fragments produces almost neutral atoms but the CH dipoles add up to give a molecular moment of 0.685 D, in excellent agreement with experiment. They also contribute to a net charge contraction towards the center of mass, whose calculated anisotropy agrees satisfactorily with the measured quadrupole moments. Multipole moments of the atomic deformation densities and inner moments of the total molecular charge about the atomic centers provide a detailed quantitative characterization of the charge distribution.     

Catalytic regioselectivity control in ring-opening cycloisomerization of methylene- or alkylidenecyclopropyl ketones

2-Methylene- or alkylidenecyclopropanyl ketones were easily prepared by the regioselective cyclopropanation of allenes or the reaction of methylene-/alkylidenecyclopropanyllithium with N,N-dimethyl carboxylic acid amides. Due to the presence of the exo-cyclic C=C bond and the strained cyclopropane, their highly selective ring-opening cycloisomerization using PdCl(2)(CH(3)CN)(2), NaI (or PdCl(2)(CH(3)CN)(2) + NaI), and Pd(PPh(3))(4) as catalysts provided five different products, i.e., 4H-pyrans, 2,3,4-trisubstituted furans (or 4,5-disubstituted-3-alkylidene-2,3-dihydrofurans), and 2,3,4,5-tetrasubtituted furans (or 2,4,5-trisubstituted-3-alkylidene-2,3-dihydrofurans) in good yields, respectively, depending on the nature of the catalyst and reaction conditions. The less-substituted C=C bonds in these products can be highly selectively hydrogenated or hydroborated to afford new heterocyclic products stereoselectively. These three types of different reactions may proceed through a highly regioselective cleavage of a carbon-carbon single bond in the cyclopropane ring triggered by regioselective halometalation of the C=C bond and beta-decarbopalladation, halogen anion attack on the nonsubstituted carbon atom of the cyclopropane ring, or the direct oxidative addition of the distal carbon-carbon single bond of the cyclopropane ring with Pd(0). In some cases substituent effects were successfully applied to synthesize 2H-pyrans 8 and 3-alkylidene-2,3-dihydrofurans 5, which also provided some mechanistic information.     

Bromination of exo-Tricyclo[3.2.2.0(2,4)]non-6-ene

In carbon tetrachloride reaction of 1 with bromine occurs at the double bond and is favored from the less hindered face, anti to the cyclopropane ring, to give 2 and 3 (2:1) over reaction from the syn face or at the corner of the cyclopropane to give 5. In the solvent methanol, corner attack of bromine at the cycloproane to give 30, 16, 17, and 37 competes with reaction at the double bond anti to the cyclopropane to give 18, 19, and 2.     

One pot synthesis of chrysanthemic esters analogs

Chrysanthemic esters analogues diversely substituted on the cyclopropane ring and on the carbon-carbon double bond can be conveniently prepared in one pot from methyl 4-oxobutenoate by delayed addition of two differently substituted phosphorus ylides.     

Dynamic equilibrium between dissociation and regeneration of the C-C bond in trispiro-conjoined cyclopropane compound

-The oxidation of 2,2-di(3,5-di-t-butyl-4-hydroxyphenyl)indan-1,3-dione by potassium hexacyanoferrate(III) afforded a trispiro-conjoined cyclopropane compound due to the bond formation between the ipso-carbons. Its cyclopropane ring was found to exist in solution in dynamic equilibrium with biradical species by the dissociation of the C-C bond, which is as long as 1.595 Å as revealed by X-ray crystal analysis.     

Cyclopropane formation from 4,5-unsaturated thiophenylethers: Conversion of limonene into car-2-ene

Strong bases can abstract a proton α to double bond. A phenylthio group ψ to that double bond can be eliminated at the same time leading to a cyclopropane ring. The procedure is illustrated by a conversion of limonene into car-2-ene.     

Halonium-initiated C-O bond formation via umpolung of α-carbon to the carbonyl: efficient access to 5-amino-3(2H)-furanones

Highly efficient C-O bond formation has been developed via carboxylic acid catalyzed reaction of 1-acetylcyclopropanecarboxamides with N-halosuccinimide (NXS), which provides strategically novel and atom-economic access to biologically important 5-amino-3(2H)-furanones. The mechanism of halonium-initiated tandem oxa-cyclization and ring opening of cyclopropane was proposed. A variety of nucleophiles were found to open the cyclopropane.     

Reactions of methylated cyclopropanes and olefins with chloroplatinic acid. I. Diacylation and pyrylium ion formation

In contrast to cyclopropane itself, simple methyl-substituted cyclopropanes do not produce platinum insertion products upon reaction with chloroplatinic acid in acetic anhydride. Instead, the major products are aromatic heterocyclic cations, the pyrylium ions, which are formed as the result of diacylation of the cyclopropane ring and subsequent dehydration and ring closure to the aromatic heterocycle. Similar products are formed from the diacylation of certain olefins in the presence of chloroplatinic acid in anhydride solvents. The combination of solvent and substrate variations has led to a proposed mechanism for these reactions which demonstrates the essential and unique mole of platinum. In particular, the specific pyrylium ions produced are formed as a consequence of initial activation of the least-substituted cyclopropane ring bond by insertion of platinum, followed by acylation of platinum-bonded carbon, proton loss to a β,γ-unsaturated carbonyl, a second acylation, and, finally, ring closure.     

Stereochemistry modulates the catalytic hydrogenolysis of nitrile-substituted cyclopropanes

The study of Raney-Ni catalyzed chemo- and regioselective hydrogenolysis of diastereomeric nitrile-substituted spirocyclopropyloxindoles is presented. The chemoselectivity outcome of the reaction is remarkably influenced by the relative stereochemistry of the nitrile-substituted spirocyclopropyloxindoles. Chemo- and high regioselective cyclopropane ring-opening occurs from the syn diastereomers to give the corresponding 3-propylacetamide derivatives. X-ray crystallographic studies together with DFT model chemistry calculations indicate that chemo- and regioselectivity are directly dependent on the bond length asymmetry of the cyclopropane ring.     

Molecular complexes of cyclopropane with hydrogen halides and water studied by matrix-isolation vibrational spectroscopy

Infrared spectra of cyclopropane-hydrogen halide and cyclopropane-water complexes show similar perturbations of the cyclopropane modes, suggesting that all have the proton donor “hydrogen-bonded” to the ring edge. The spectrum of the cyclopropane-water complex is consistent with water forming a bifurcated hydrogen bond to the ring.     

Nitrile anion cyclization with epoxysilanes followed by Brook rearrangement/ring-opening of cyclopropane nitriles/alkylation

[reactions: see text] The reaction of delta-silyl-gamma,delta-epoxypentanenitrile derivatives 9-12 with a base and an alkylating agent affords (Z)-delta-siloxy-gamma,delta-unsaturated pentanenitrile derivatives via a tandem process that involves the formation of a cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring. Exclusive formation of a (Z)-derivative from trans-epoxides is explained by the reaction pathway that involves a backside displacement of the epoxide by the alpha-nitrile carbanion and the O-Si bond formation followed by concerted processes involving Brook rearrangement and the anti-mode of eliminative ring fission of the cyclopropane from the rotamer 19. The fact that (E)-isomers are exclusively obtained from cis-epoxides and alpha-cyclopropyl-alpha-silylcarbinol derivative 26 provides experimental support for the proposed pathway.     

Photolyse von 2, 2, 4, 4-Tetramethylcyclobutanon-Derivaten

The photochemical reactions of the 2, 2, 4, 4-tetramethylcyclobutanones 1–6 carrying various substituents in 3-position were investigated. The major reaction in alcoholic solution or in the presence of other protic compounds was the formation of the semicyclic acetals 7–12 . Parallel to this reaction decarbonylation occurred, leading to stable cyclopropane derivatives in some cases, depending on the substituents present. Cyclopropanes with an exocyclic double bond underwent ring opening easily or, in case of an exocyclic carbon-nitrogen double bond, added alcohol, thus forming cyclopropane O, N-ketals. Alkyl-acyl biradicals are proposed as common intermediates for both photoreactions. Based on analogy to similar photoreactions reported in the literature, the formation of the semicyclic acetals is assumed to involve a carbene intermediate.     

Hybridization in methylenecyclopropane and related molecules having exocyclic double bonds

The hybridization in methylenecyolopropane, dimethylenecyclopropane, bisethanoallene, and related molecules containing double bonds externally attached to a cyclopropane ring is considered by applying the method of maximum overlap. The results show that the bond overlap of an exocyclic double bond is larger than the bond overlap of a normal C=C bond, and double bonds in allenes have even larger overlap than an exocyclic C=C bond. The results of the calculations are correlated with some available experimental data.     

Biomimetic approach to perophoramidine and communesin via an intramolecular cyclopropanation reaction

[reaction: see text] Starting from tryptamine 4 and isatin 5, a biomimetic approach to the pentacyclic substructure 1 of perophoramidine and communesin was developed. The key steps were to create a stable three/six bicyclic system 2 on the 2,3-double bond of an indole derivative 3 by an intramolecular cyclopropanation, followed by ring opening of the resulting cyclopropane ring with the in situ generated amine group of an aniline.     

Local orbital study of bonding in small rings: Cyclopropane,thiirane, oxirane,and aziridine

The nature of the bonding in the three-membered ring molecules cyclopropane, thiirane, oxirane, and aziridine has been investigated throughab initio FSGO calculations. The direct correspondence between floating spherical Gaussian orbitals and specific chemical bonds has been used to study the degree of “bond bending”. In accord with chemical intuition, it is demonstrated that the C-C ring bond becomes progressively more bent as the bond length is reduced. C-C bonds are found to be more flexible than C-N (O, S) bonds. The sizes and locations of carbon-heteroatom bond orbitals and C-H bond orbitals are also discussed.     

Cyclopropane Adsorption on Zeolites Studied by IR Spectroscopy: II. Adsorption and Conversion of Cyclopropane on Na- and Ca-Exchanged Zeolite Y

The adsorption and isomerization of cyclopropane on the calcium- and sodium-exchanged zeolite Y are studied by IR spectroscopy. Cyclopropane is adsorbed on CaY in two different forms. Weaker adsorption is related to residual sodium ions, which were not completely removed from the zeolite by ion exchange. This form can be removed from the surface after evacuation of the samples at room temperature. Stronger adsorption is attributed to the Ca ions. It is stable up to 100°C. The corresponding diffuse-reflectance spectrum indicates the C _2v symmetry of the cyclopropane complex with Ca ions. At 200°C cyclopropane adsorbed on the calcium-exchanged zeolite converts to propylene. On the sodium-exchanged zeolite, this reaction only occurs at 400°C. The reaction coordinate of cyclopropane isomerization on CaY is related to the simultaneous cleavage of the C–C bond in the cyclopropane ring and hydrogen atom transfer from one of the CH₂ fragments to another. The reaction coordinate corresponds to a combination of the stretching vibration of the C–C bond with the fan vibration of the CH₂ group and the stretching vibration of the CH bond. These composite vibrations result in the strong polarization of the C–C and C–H bonds and, hence, exhibit anomalously high molar absorption coefficients in the IR spectrum.     

Ring opening reaction of gem-difluorocyclopropyl ketones with nucleophiles

Syntheses of gem-difluorocyclopropyl ketones (3a–d) and their reactions with nucleophiles are described. Ring opening reactions of 3a,c and d with a methanolate and a thiolate anion took entirely different courses of bond scission of the cyclopropane ring.