Intramolecular nucleophilic substitution at an sp carbon: synthesis of substituted thiazoles and imidazole-2-thiones

The nucleophilic substitution reactions of vinylic bromides with intramolecular thioamide or thiourea moieties proceed to give a series of substituted thiazoles and imidazole-2-thiones.     

Vicarious nucleophilic substitution of hydrogen versus vinylic substitution of halogen in the reactions of carbanions of halomethyl aryl sulfones with dialkyl halofumarates and halomaleates

Reaction of halomethyl aryl sulfone carbanions with dialkyl halofumarates and halomaleates results in nucleophilic substitution of hydrogen and/or of the halogen. The reaction with halofumarates proceeds via addition of the carbanions to the vinylic carbon atom connected with hydrogen, followed by base promoted β-elimination of hydrogen halide in which the halogen originates from the carbanion moiety or from the alkene. In the case of halomaleates the reaction proceeds via an elimination-addition sequence.     

Vinylic nucleophilic substitution in functionalized 2-vinylpyrroles: a route to a new family of stable enols

2-(2-Cyano-1-ethylthioethenyl)pyrroles easy exchange their ethylthio group for hydroxyl (NaOH, H₂O-methanol, 40-45 °C, 1 h) to give 2-(2-cyano-1-hydroxyethenyl)pyrroles, a new family of stable enols, in 50-94% yields. The vinylic nucleophilic substitution proceeds at the double bond of both the starting pyrroles and their cyclic isomers, 3-iminopyrrolizines. X-ray structure analysis and NMR spectra show the enols to be stabilized by exceptionally strong intramolecular H-bonding.     

Synthesis of vinylic iodides for incorporation into the C17-C27 fragment of bryostatins

Vinylic iodides were identified as useful intermediates for the synthesis of the C17-C27 fragment of the bryostatins with control of the geometry of the exocyclic methoxycarbonylmethylene group. Following literature precedent, the Piers (E)-stereoselective addition of tributyltin hydride to an alkynoate followed by ester reduction and tin-iodine exchange gave vinylic iodides that could be used to form the C20-C21 bond of the bryostatins. Chelation controlled addition of lithiated 3-silyloxypropynes to 2-alkoxyaldehydes followed by reductive iodination was used to prepare vinylic iodides that could be used in the complementary assembly of the C21-C22 bond of the bryostatins. Initial studies of the synthesis of intermediates for metathesis studies using metal catalysed reactions of a vinylic iodide for C21-C22 bond formation were complicated by cyclisation reactions.     

Synthesis of 1,3-enynes via Suzuki-type reaction of vinylic tellurides and potassium alkynyltrifluoroborate salts

The palladium-catalyzed cross-coupling reaction between potassium alkynyltrifluoroborate salts and vinylic tellurides proceeds readily to afford 1,3-enynes with moderate to good yields.     

Synthesis of polyacetylenic acids isolated from Nanodea muscosa

The first total synthesis of two linear polyacetylenic compounds is described. The synthesis of (E)-octadec-13-en-11-ynoic acid 1 and (E)-octadec-13-en-9,11-diynoic acid 2 by using the vinylic telluride coupling reaction was accomplished.     

Michael addition-elimination mechanism for nucleophilic substitution reaction of cycloalkenyl iodonium salts and selectivity of 1,2-hydrogen shift in cycloalkylidene intermediate

Reactions of cyclohexenyl and cyclopentenyl iodonium salts with cyanide ion in chloroform give cyanide substitution products of allylic and vinylic forms. Deuterium-labeling experiments show that the allylic product is formed via the Michael addition of cyanide to the vinylic iodonium salt, followed by elimination of the iodonio group and 1,2-hydrogen shift in the 2-cyanocycloalkylidene intermediate. The hydrogen shift preferentially occurs from the methylene rather than the methine beta-position of the carbene, and the selectivity is rationalized by the DFT calculations. The Michael reaction was also observed in the reaction of cyclopentenyliodonium salt with acetate ion in chloroform. The vinylic substitution products are ascribed to the ligand-coupling (via lambda3-iodane) and elimination-addition (via cyclohexyne) pathways.     

Synthesis of hetero- and carbocycles by nucleophilic substitution at sp carbon

Vinylic halides having alcohol, sulfonamide, active methine, and thiol moieties as nucleophiles cyclize to hetero- and carbocycles by intramolecular nucleophilic substitution at the sp² carbon centers. The density functional theory calculations suggest that the cyclization proceeds through S_N2-type substitution (the in-plane vinylic nucleophilic substitution, S_NVσ), when vinyl halides are substituted with oxygen, nitrogen, and carbon nucleophiles. The substitution with sulfur nucleophiles, in contrast, proceeds through both routes of S_NVσ and out-of-plane vinylic nucleophilic substitution (S_NVπ).     

Rare example of nucleophilic substitution at vinylic carbon with inversion: mechanism of methyleneaziridine formation by sodium amide induced ring closure revisited

Intramolecular nucleophilic substitution of the C-Br bond of (E)- and (Z)-2-bromobut-2-enylamines by the pendant nitrogen atom leads to 2-ethyleneaziridines by way of stereochemical inversion at the vinylic carbon atom. The stereochemistry of the products is unambiguously established by X-ray crystallography performed on two derivatives. These cyclizations represent some of the first examples of substitution with inversion in unactivated vinylic substrates. In conjunction with additional deuterium-labeling experiments, the accepted mechanism for this reaction is shown to be flawed.     

Nucleophilic vinylic substitutions on unactivated substrates. : The behaviour of styryl alkyl sulphides and selenides towards sulphur and selenium nucleophiles.

Sodium alkanethiolates or lithium methyl selenide react with styryl alkyl sulphides and selenides, in DMF at 100°C, to give the products of vinylic or aliphatic substitution. The two nucleophilic reagents are extremely selective. In the case of RSNa the attack at the vinylic carbon atom is much faster than that at the aliphatic carbon atom and the (Z)- or (E)- styryl alkyl sulphides are obtained as the result of a stereospecific vinylic substitution which occurs with retention of configuration. On the contrary, in the case of MeSeLi, under the same experimental conditions, the only reaction occurring is the aliphatic substitution which affords the vinyl thiolate anions, as an equilibrium mixture of the (E)- and (Z)- isomers, or the vinyl selenide anions which retain the configuration of the starting styryl alkyl selenides.     

Homologous SNV Reaction: Synthesis of l‐Methyl‐4‐[4′‐phenylsulfonyl‐1′,3′‐butadienyl]pyridinium Iodide and Its Reactivity with Thiol Groups Giving Rise to the Chromophoric Thioether

Thioether 4‐[(1′E,3′E)‐4′‐phenylsulfanyl‐1,3′‐butadienyl]pyridine 8 and sulfone 4‐(4′‐phenylsulfonyl‐1′,3′‐butadienyl)pyridine 14 were prepared by reaction of the carbanions derived from allylic thioether or allylic sulfone with isonicotinaldehyde. The reaction with the sulfonyl carbanion occurred at the α position and on heating the alcolate gave the dienic sulfone 14 . The corresponding pyridinium iodide 10 and 15 were prepared by reaction with methyl iodide, respectively, on pyridine derivates 8 and 14 . The dienic pyridinium thioether 10 showed a long wavelength absorption band centered at 420 nm. The reaction of dienic pyridinium sulfone 15 with thiophenol gave the dienic pyridinium thioether 10 by a nucleophilic vinylic substitution. The reaction of sulfone 15 with glutathione was of second order and the rate constant was 8.5 M^?1s^?1 at 30°C and pH 7, about 500 times smaller than the rate constant observed with (E)‐1‐methyl‐4‐(2‐methylsulfonyl‐1‐ethenyl)pyridinium iodide 1 . The dienic pyridinium thioether 10 was a negative solvatochrome.     

新型PA/PU复合涂料的合成与性能研究

合成了一种高固含量、不含异氰酸根并可在室温固化的新型聚丙烯酸酯－聚氨酯复合涂料（简写为ＰＡ－ＰＵ），其中ＰＡ为侧基含乙酰乙酸基的聚丙烯酸酯，ＰＵ为端烯基聚氨酯。碱催化下，通过具有两个活泼氢的乙酰乙酸基与双键的Ｍｉｃｈａｅｌ加成反应进行交联固化。主要研究了两组份的合成规律及ＰＡ－ＰＵ涂料的性能，结果表明在一定的催化剂用量下，漆膜具有优良的性能     

Electrophilic Substitution of Hydrogen in Betulin and Diacetylbetulin

Betulin and diacetylbetulin, which can be regarded as sterically hindered alkenes, reacted with N-chloro-, N-bromo-, and N-iodosuccinimides to give products of allylic and vinylic substitution in quantitative overall yield. The contribution of allylic substitution increases in the series Cl < Br < I. Quantum chemical simulation of the reactions of diacetylbetulin with N-halosuccinimides showed that, regardless of the electrophile power, all reactions involve open-chain carbocationic intermediates. The direction of deprotonation of the latter with formation of allylic or vinylic substitution products is determined by preferential orientation of the vacant orbital and C–Hlg bond.     

A novel example of vinylic SRN1: Reactions of 3,3-difluoro-1-iodo-2-phenylcyclopropene with thiolate ions

The reactions of 3,3-difluoro-1-iodo-2-phenylcyclopropene with thiolate ions (with a molar ratio of 1:1) were carried out in laboratory illumination to give the corresponding substituted product. The presence of p-dinitrobenzene (p-DNB) or hydroquinone (HQ) as well as darkness significantly suppressed the reaction. ESR trapping experiments also evidenced the existence of fluorinated radical. All these results demonstrate the reaction involved a vinylic saturated alkyl and aromatic halides (S_RN1) mechanism.     

Nucleophilic substitution reaction at an sp carbon of vinyl halides with an intramolecular thiol moiety: synthesis of thio-heterocycles

This article presents a full account of intramolecular vinylic substitution reactions of bromoalkenes having an acetylthio moiety, which give sulfur-containing heterocycles such as dihydrothiophene, tetrahydrothiopyran, and 2-alkylidenethietane derivatives. The reaction pathways of the substitution reactions were investigated by theoretical and experimental studies.     

Substitution nucleophile vinylique par le reactif de reformatsky catalysee par des complexes du nickel et du palladium zerovalents. Synthese d'esters β,γ-ethyleniques

Zerovalent complexes of palladium and nickel catalyse vinylic nucleophilic substitution by the Reformatsky reagent giving β,γ-ethylenic esters. Formation of a σ-vinylpalladium complex is the rate-determining step of the reaction.     

Organocatalytic enantioselective nucleophilic vinylic substitution by alpha-substituted-alpha-cyanoacetates under phase-transfer conditions

The organocatalytic enantioselective formation of vinyl-substituted all-carbon quaternary stereocenters via nucleophilic vinylic substitution by alpha-substituted-alpha-cyanoacetates is presented. The reaction proceeds well for different alpha-substituted-alpha-cyanoacetates and beta-chloroalkenones using a dimeric cinchona alkaloid phase-transfer catalyst giving the products in good yield and with enantioselectivities up to 98% ee.     

O-attack versus N-attack: electrophilic halocyclization of unsaturated amides with vinylic halogen substitution

Electrophilic iodocyclization of unsaturated amides with an internal vinylic halogen (Cl, Br, or I) substitution afforded exclusively the corresponding cyclic iminoketones via iodolactamization. On the other hand, amides having a terminal vinylic halogen substituent underwent iodolactonization only. Theoretical calculations revealed that the iodocyclization proceeds via the intramolecular iodonium ion transfer from the amide nitrogen to the C=C double bond.     

The Influence of Monomers upon Microemulsions with Short Chain Cosurfactant

Several monomers (i.e., acrylonitrile (ACN), ethyl acrylate (EtA), acrylate of 2 ethylhexyl (EHA), butyl acrylate (BuA), vinyl acetate (VAc), methyl methacrylate (MMA) and styrene (St)) were investigated in order to study their capacities to form microemulsions. The surfactant was nonyl phenol ethoxylate with 25 moles ethylene oxide and ethanol was used as the cosurfactant. The phase diagrams prove that the capacity for microemulsion formation varies in the following sequence: ACN = EtA > VAc > BuA > MMA > St > EHA. Conductometric and refractometric studies allowed us to evidence the formation of microemulsions with W/O, bicontinuous or O/W structure. Fluorescence studies give interesting informations on the stabilization capacity of the monomers dispersed by interaction with hydrophobic chain of the cosurfactant. H-NMR studies suggest that the monomers in microemulsions lie in regions with various polarities as function of their chemical nature. In polymerization initiated with benzoyl peroxide the minimum conversions were obtained in zones of composition where the initial microemulsions possess a bicontinuous microstructure. The reactions of degradative transfer of the increasing macroradicals account for these conversion modifications. For initiation with ammonium persulphate, its rate of decomposition depends on its ability to displace the proton bonded to the substituted vinylic carbon of the monomer. The productivity of this initiator varies within the sequence MMA > EtA > BuA > St > ACN > VAc. The consumption of the initiator, as induced by the monomer, depends on its chemical nature and on the solubilization site of the microemulsions.     

Stereoselective synthesis of vinylic (Z)-vic-bis(arylchalcogenides)

Alkyne-titanium complexes 3, readily prepared in situ by the reaction of alkynes with Ti(O-i-Pr)₄/2 i-PrMgCl, react with electrophilic chalcogen species under mild conditions to provide the corresponding addition products in fair to good yields. The obtained vinylic vic-bis(arylchalcogenides) 4 are useful synthetic intermediates for introducing vinyl functions into organic molecules.