α-Indolyl-β-nitroacrylates. Synthesis and structure

A one-pot procedure has been developed for the synthesis of α-indolyl-β-nitroacrylates by reaction of β-bromo-β-nitroacrilates with indole and substituted indoles. All indolylnitroacrilates thus obtained have Z configuration of the double bond. According to the X-ray diffraction data, ethyl 2-(1-methyl-1H-indol-3-yl)-3-nitroacrylate is characterized by s-trans conformation of the double C=C bond and indole ring; its crystal packing involves intermolecular hydrogen bonds C-H…O and C-H…π with formation of centrosymmetric dimers which give rise to bilayer supramolecular structures.     

(tBu2MeSi)2Sn=Sn(SiMetBu2)2: a distannene with a >Sn=Sn< double bond that is stable both in the solid state and in solution

((t)Bu(2)MeSi)(2)Sn=Sn(SiMe(t)Bu(2))(2) 1, prepared by the reaction of (t)Bu(2)MeSiNa with SnCl(2)-diox in THF and isolated as dark-green crystals, represents the first example of acyclic distannene with a Sn=Sn double bond that is stable both in the crystalline form and in solution. This was proved by the crystal and NMR spectral data of 1. Distannene 1 has these peculiar structural features: a shortest among all acyclic distannenes Sn=Sn double bond of 2.6683(10) A, a nearly planar geometry around both Sn atoms, and a highly twisted Sn=Sn double bond. The reactions of 1 toward carbon tetrachloride and phenylacetylene also correspond to the reactivity anticipated for the Sn=Sn double bond. The one-electron reduction of 1 with potassium produced the distannene anion radical, the heavy analogue of alkene ion radicals, for which the particular crystal structure and low-temperature EPR behavior are also discussed.     

Alkyl 2-(2-benzothiazolylsulfinyl)acetates as useful synthetic reagents for alkyl 4-hydroxyalk-2-enoates by sulfinyl-Knoevenagel reaction

Isopropyl, ethyl, and methyl 2-(2-benzothiazolylsulfinyl)acetates have been found to be useful synthetic reagents for sulfinyl-Knoevenagel reaction with various aldehydes to give directly the corresponding 4-hydroxyalk-2-enoates [R′CH(OH)CHCHCO₂R], which are ubiquitous structures in biologically active natural products and useful building blocks for organic synthesis of chiral compounds. From the optically pure (R)-2-(2-benzothiazolylsulfinyl)acetates (>99% ee) prepared by the enzymatic kinetic resolution of (±)-2-(2-benzothiazolylsulfinyl)acetates, optically active 4-hydroxyalk-2-enoates (up to 91% ee) have been obtained in good yields.     

[2 + 2] Cycloaddition reactions of unsymmetrically substituted carbodiimides

N-Alkyl-N′-arylcarbodiimides add alkyl and aryl isocyanates to the N-alkyl substituted CN double bond to yield 4-arylimino-1,3-diazetidine-2-ones 3. In the case of bulky alkyl substituents the reaction still proceeds across the sterically hindered CN double bond. N-Aryl-N′-[(4-dimethylamino)phenyl]carbodiimides form [2 + 2] cycloadducts with aryl isocyanates preferentially across the CN double bond not attached to the electron-rich aryl groups. However, steric crowding on this CN double bond directs the reaction to the adjacent double bond of the heterocumulative system. The rate of the [2 + 2] cycloaddition reaction of N'-methyl-N′-phenylcarbodiimide with 4-nitrophenylisocyanate is about 2.5 times faster in acetonitrile than in benzene.     

Convenient synthesis of 2-(het)arylpyrrolidines via stable 1-pyrrolinium salts

The efficient method for the synthesis of 2-(het)aryl-substituted pyrrolidines possessing exocyclic carbon-carbon double bond via the Mannich-type reaction of stable 3-arylidene-1-pyrrolinium salts with different heterocyclic C-nucleophiles is proposed.     

Etude théorique par la méthode DFT des structures non-classiques des systèmes X2H2F2 (X=Si, Ge, Sn)

The structure and the relative stability of isomers of molecules X₂H₂F₂ (X=Si, Ge, Sn) have been studied using the density functional theory (DFT). We have determined the optimised structures of the substituted isomers. The XX bond have been studied and compared to that of the parent molecules: X₂H₄. It appears that, for the planar and trans ethylenic systems, the double bond character of the XX decreases when the hydrogen atoms are substituted by fluorine atoms. The most stable structure is shown to be the one where the two fluorine atoms are fixed on the same atom. The bridged structures are also studied.     

Controlling degradation and branching reactions of polypropylene by different heteroaromatic ring derivatives

Heteroaromatic ring derivatives with the CC bond conjugated with different five-membered heteroaromatic rings were used to adjust melt reaction of polypropylene (PP). The effect of heteroatoms in the five-membered rings and electron-attracting groups connecting with CC bond on restricting the β-scission of PP macroradicals and promoting the branching reaction between PP and trimethylol propane triacrylate (TMPTA) was studied. From the analysis of the results concerning molecular structures and melt properties, it was found that the electron density of the CC bond determined the reaction rate between PP macroradicals and heteroaromatic ring derivatives. 2-cyano-3-(furan-2-yl)-2-propenoic acid ethyl ester (CFA) and 2-(furan-2-ylmethylene)malononitrile (FN) had CC bonds with lower electron density, therefore they can quickly convert the tertiary PP macroradicals into resonance stabilized macroradicals. As a result, the β-scission of PP macroradicals and the homopolymerisation of TMPTA were restrained to some extent. Modified PP samples containing TMPTA, peroxide and CFA (or FN), which had the lower grafting degree of TMTPA, showed the most obvious change on the relaxation behaviour of polymer chains.     

New domino reaction. One pot synthesis of 4,7-dihydroxythioaurone derivatives from benzaldehydes and 4-acetyl-2-oxo-benz[1,3]oxathiole

A convenient synthesis of 4,7-dihydroxythioaurone derivatives by a one pot reaction of benzaldehydes with 4-acetyl-2-oxo-benz[1,3]oxathioles and piperidine acetate in DMSO is described. The structures of the compounds, including double bond geometry were proved unequivocally by NMR methods. The thioaurone ring system seems to be formed by three consecutive reactions: opening of the oxathiolone ring with piperidine, oxidation of the formed mercapto group with DMSO or/and air to disulfide, and condensation with aldehyde.     

Natural (5-oxoheptene-1E,3E-dienyl)-5,6-dihydro-2H-pyran-2-one: total synthesis and revision of its absolute configuration

The synthesis of (5^′-oxoheptene-1^′E,3^′E-dienyl)-5,6-dihydro-2H-pyran-2-one has been performed in seven steps using four key steps: a ring-closing metathesis reaction to build up the unsaturated lactone, a Wittig reaction to control the C6-C7 (E) double bond, a cross-metathesis reaction to control the (E) double bond at C8-C9, and an enantioselective allyltitanation to control the absolute configuration at C5. Spectroscopic data (IR, MS, ¹H, and ¹³C NMR) were identical to those of the natural compound except for the optical rotation, which led us to re-assign the absolute configuration of the natural product.     

Kinetics and thermochemistry of the [2π+2σ+2σ]-cycloaddition of quadricyclane with 2,3-dicyano-1,4-benzoquinone

Two-stage [2π+2σ+2σ]-cycloaddition of quadricyclane ( 2 ) with 2,3-dicyano-1,4-benzoquinone ( 1 ) with a huge difference in the activity of two reaction centers has been studied. In the first stage (kinetic control), the cycloaddition of 2 takes place on the activated С₂=С₃ bond of 1 to form the monoadduct 3 , and in the second stage the cycloaddition of 2 on the С₅=С₆ bond of the monoadduct 3 occurs by 6 orders of magnitude lower with the formation of bisadduct 4 . The structures of adducts 3 and 4 have been proved by NMR data and the X-Ray method, respectively. The kinetics of the first and second stages, the enthalpy of dissolution of 1 in the π-donor solvents, and the enthalpy of the reaction 1+2→3 have been measured.     

Unexpected regioselectivity observed in the bromination and epoxidation reactions of p-benzoquinone-fused norbornadiene: An experimental and computational study

The bromination reaction of p-benzoquinone-fused norbornadiene was studied at various temperatures (?78, ?50, 0, 25, and 77 °C). At room temperature, the double bonds of the p-benzoquinone units were mainly brominated. The double bond of the norbornene unit also underwent a bromination reaction in a yield of only 2%. However, the reaction at ?78 °C resulted in the formation of products derived from the attack of bromine on the norbornene double bond with higher charge density. In contrast to the bromination reaction, the epoxidation reaction of the same compound with m-chloroperbenzoic acid and dimethyldioxirane exclusively resulted in the formation of products derived from the addition to the double bond of norbornadiene. The regioselectivity observed was investigated and the results were supported by theoretical calculations.     

(-)-Menthol as a source of new N,N-diamine ligands for asymmetric transfer hydrogenation

The synthesis of new chiral N-monotosylated-1,2-diamines based on the (-)-menthol skeleton is presented. The elimination of HCl from neomenthyl chloride obtained from an Appel reaction led to p-menth-3-ene in excellent yield. Further functionalization of the double bond in p-menth-3-ene with chloramine-T gave the corresponding N-tosylaziridines, which upon reaction with sodium azide and subsequent reduction of the azide functional group, formed the 1,2-diamine system. The synthesized chiral ligands proved effective in the asymmetric transfer hydrogenation of aromatic ketones and an endocyclic imine.     

A convenient synthesis of 1,2-difluoro-1, 2-dideoxyhexoses using xenon fluoride

A method for the addition of fluorine to the double bond in acetylated glycals using XeF₂ in the presence of BF₃ has been shown to provide a convenient route for the synthesis of acetylated 1, 2-dideoxy-1, 2-difluorosugars. The reagent attacks the double bond predominantly from the least hindered side to give a cis adduct, but the reaction also provided other isomers which have been separated by chromatography and their stereo-chemistry determined by ¹⁹F NMR spectroscopy. The proposed mechanism of the reaction involves an initial electrophilic attack by the reagent on C-2 followed by a nucleophilic attack on C-1. Deacetylation of the adducts gave 1, 2-dideoxyl-1, 2-difluorosaccharides, which are of interest in biochemical studies. A crystalline 2-deoxy-2-l-fucose was prepared by selective hydrolysis of the anomeric fluorine atom of 1, 2-dideoxy-1, 2-difluoro-l-fucose.     

Free-radical cyclization of enantiomerically enriched 2-p-tolylthio derivatives of 2-allylcyclohexanones with Mn(III): asymmetric synthesis of bridged bicyclic ketones and thiochroman-3-ones

Mn(III)-based oxidative intramolecular cyclization of enantiomerically enriched 2-allyl-2-(p-tolylsulfonyl)-cyclohexanone 4 and 2-allyl-2-(p-tolylsulfenyl)cyclohexanone 9 are reported. The observed chemoselectivity (reaction on the allylic double bond yielding bridged bicyclic ketones vs. reaction on the aromatic ring of the p-tolyl group affording thiochroman-3-ones) depends on the sulfur function (sulfone or thioether, respectively), which determines the electronic density of the p-tolyl ring and the conformational preferences of the starting compounds. The nature of the substituent at C-2 is related to the endo/exo selectivity of the cyclization as well as the regioselectivity in the formation of the enones.     

Cyclopropanation of methyl (2<Emphasis Type="Italic">E</Emphasis>)-3-[(1<Emphasis Type="Italic">R</Emphasis>,6<Emphasis Type="Italic">S</Emphasis>)-7,7-dimethyl-2-oxo-3-oxabicyclo[4.1.0]hept-4-en-4-yl]prop-2-enoate with dichlorocarbene and diazomethane

Cyclopropanation of methyl (2E)-3-[(1R,6S)-7,7-dimethyl-2-oxo-3-oxabicyclo[4.1.0]hept-4-en-4-yl]prop-2-enoate with dichlorocarbene occurred at the endocyclic double bond, while its reaction with diazomethane in the presence of Pd(acac)₂ involved the exocyclic double bond. The resulting lactones reacted with sodium methoxide in methanol via opening of one cyclopropane fragment.     

Stereoselective Rhodium‐Catalysed [2+2+2] Cycloaddition of Linear Allene–Ene/Yne–Allene Substrates: Reactivity and Theoretical Mechanistic Studies

Allene–ene–allene ( 2 and 5 ) and allene–yne–allene ( 3 and 7 ) N‐tosyl and O‐linked substrates were satisfactorily synthesised. The [2+2+2] cycloaddition reaction catalysed by the Wilkinson catalyst [RhCl(PPh₃)₃] was evaluated. Substrates 2 and 5 , which bear a double bond in the central position, gave a tricyclic structure in a reaction in which four contiguous stereogenic centres were formed as a single diastereomer. The reaction of substrates 3 and 7 , which bear a triple bond in the central position, gave a tricyclic structure with a cyclohexenic ring core, again in a diastereoselective manner. All cycloadducts were formed by a regioselective reaction of the inner allene double bond and, therefore, feature an exocyclic diene motif. A Diels–Alder reaction on N‐tosyl linked cycloadducts 8 and 10 allowed pentacyclic scaffolds to be diastereoselectively constructed. The reactivity of the allenes on [2+2+2] cycloaddition reactions was studied for the first time by density functional theory calculations. This mechanistic study rationalizes the order in which the unsaturations take part in the catalytic cycle, the reactivity of the two double bonds of the allene towards the [2+2+2] cycloaddition reaction, and the diastereoselectivity of the reaction.     

Novel synthesis of 2-aminopentanedinitriles from 2-(bromomethyl)aziridines and their transformation into 2-imino-5-methoxypyrrolidines and 5-methoxypyrrolidin-2-ones

1-Arylmethyl-2-(bromomethyl)aziridines were transformed into 2-[N-(arylmethyl)amino]pentanedinitriles upon treatment with an excess of potassium cyanide in DMSO through an unprecedented and peculiar reaction mechanism, involving base-induced ring opening of intermediate 2-(cyanomethyl)aziridines into allylamines, followed by migration of the double bond out of the conjugation towards aldimines via enamine intermediates. The resulting aminopentanedinitriles served as substrates for the synthesis of novel 2-imino-5-methoxypyrrolidines upon treatment with sodium methoxide in methanol, which were either acetylated at the free imino group to afford the more stable N-acetylimino derivatives or hydrolyzed towards the corresponding synthetically relevant 5-methoxypyrrolidin-2-ones.     

Effects of N-substitution on the fragmentations of some cyclohexene-fused 2-N-phenyliminoperhydro-3,1-oxazines and related thiazines

Six cyclohexene-fused 2-N-phenyliminoperhydro-3,1-oxazines and four related thiazines were prepared and their mass spectrometric behavior was studied by means of metastable ion analysis and exact mass measurement. In most of the fragmentations, extensive rearrangements took place. The decompositions through the retro-Diels-Alder reaction initiated by the double bond dominated in the case of the unsubstituted compounds. The effect of the double bond, however, was greatly outweighed by the effect of the substituent on the ring nitrogen atom. In comparison with the unsubstituted compounds, both electron-releasing (methyl) and electron-withdrawing (benzyl) substituents increased the contribution of the ring cleavage reactions in the heterocyclic part of the molecule; in the case of the benzyl group the loss of the substituent also became important. For isomeric compounds, the relative peak intensities were so different that such compounds were easy to differentiate.     

Methyl (E)-2-(2-phenylcyclopropylidene)acetate: Synthesis, isomerization, and reaction with 1,3-diphenyl-2-benzofuran

Treatment of 3-methyl-2-phenylcycloprop-2-ene-1-carboxylic acid with potassium tert-butoxide induced its isomerization into trans-2-methylidene-3-phenylcyclopropane-1-carboxylic acid which was converted into methyl ester, and heating of the latter for 1 h in toluene gave methyl (E)-2-(2-phenylcyclopropylidene)acetate. Thermal isomerization of methyl (E)-2-(2-phenylcyclopropylidene)acetate on prolonged heating in toluene afforded 5-methoxy-3-methyl-2-phenylfuran, and the reaction with 1,3-diphenyl-2-benzofuran resulted in [4 + 2]-cycloaddition at the exocyclic double bond.