Vinylation of silanes and disiloxanes. Preparation of hexavinyldisiloxane

Vinylation of silanes and disiloxanes has been studied. It has been shown that in the reactions of silanes with vinyl chloride and magnesium or sodium the sole product formed is tetravinylsilane. In the reactions of hexaethoxydisiloxane with vinyl chloride and magnesium, tetravinylsilane is the sole product formed. Hexavinyldisiloxane with yield up to 85% is formed in the reaction of hexaethoxydisiloxane with vinyl chloride and magnesium in the presence of copper(II) salts as alkylation catalyst.     

Umvinylierungen mit Vinyl-phenyl-äther als Vinylierungsmittel

Vinyl interchange of vinyl phenyl ether with phenols in the presence of mercuric acetate as a catalyst gives the corresponding vinyl aryl ethers in 40–75% yields. The reaction between vinyl phenyl ether and alcohols yields isolable quantities of vinyl alkyl ethers only when this product can be removed continuously during the reaction.     

Palladium-catalyzed 1,1-difunctionalization of ethylene

The 1,1-difunctionalization of ethylene, with aryl/vinyl/heteroaryl transmetalating agents and vinyl electrophiles, is reported. The reaction is high-yielding under a low pressure of ethylene, and regioselectivity is generally high for the 1,1-disubstituted product. The process is highlighted by the use of heteroaromatic cross-coupling reagents, which have not been competent reaction partners in previously reported efforts.     

The vinyl + NO reaction: determining the products with time-resolved Fourier transform spectroscopy

We have studied the vinyl + NO reaction using time-resolved Fourier transform emission spectroscopy, complemented by electronic structure and microcanonical RRKM rate coefficient calculations. To unambiguously determine the reaction products, three precursors are used to produce the vinyl radical by laser photolysis: vinyl bromide, methyl vinyl ketone, and vinyl iodide. The emission spectra and theoretical calculations indicate that HCN + CH2O is the only significant product channel for the C2H3 + NO reaction near room temperature, in contradiction to several reports in the literature. Although CO emission is observed when vinyl bromide is used as the precursor, it arises from the reaction of NO with photofragments other than vinyl. This conclusion is supported by the absence of CO emission when vinyl iodide or methyl vinyl ketone is used. Prompt emission from vibrationally excited NO is evidence of the competition between back dissociation and isomerization of the initially formed nitrosoethylene adduct, consistent with previous work on the pressure dependence of this reaction. Our calculations indicate that production of products is dominated by the low energy portion of the energy distribution. The calculation also predicts an upper bound of 0.19% for the branching ratio of the H2CNH + CO channel, which is consistent with our experimental results.     

The reaction products of the 193 nm photolysis of vinyl bromide and vinyl chloride studied by time-resolved Fourier transform infrared emission spectroscopy

Time-resolved Fourier transform infrared (TRFTIR) emission spectroscopy has been used to study the 193 nm photolysis of vinyl bromide (C(2)H(3)Br) and vinyl chloride (C(2)H(3)Cl). Time-resolved IR emission was analysed to obtain nascent vibrational state populations of two primary photolysis products: HBr (v = 1-7) and HCl (v = 1-6). In both cases the nascent vibrational state populations monotonically decrease with increasing v and are in excellent agreement with previously published data. Time-resolved populations were analysed to yield rate constants for vibrational relaxation of HBr (v = 1-3) and HCl (v = 1-4) by parent vinyl bromide and vinyl chloride, respectively. In both cases the rate constants were found to increase with increasing vibrational quantum number, in agreement with a single quantum de-excitation via vibrational to vibrational energy transfer. Butadiene (C(4)H(6)) was identified as a secondary product of the photolysis of both vinyl halides, and shown to be formed from the reaction of parent vinyl halide with the vinyl radical. The presence of a buffer gas was found to produce a strong emission feature centred at 2,200 cm(-1), the intensity of which was dependent on the pressure of the buffer gas used, and whose kinetics are indicative of a secondary reaction product. We propose that this emission is from the vibrational progression of the electronic transition A(0, v, 1) --> X(0, v, 2) in the secondary reaction product C(2)H, whose formation route is favoured by the presence of buffer gas.     

An experimental and theoretical study of the mechanism of stannylcupration of alpha,beta-acetylenic ketones and esters

The title reaction has been investigated by experimental and computational (DFT) techniques, and subsequently compared to the corresponding carbocupration reaction, with particular emphasis on the stereoselectivity. For stannylcupration of an ynone substrate, only the anti-addition product is observed, whereas for the corresponding ynoate substrate, the stereoselectivity can be affected by the reaction conditions: in the presence of methanol as proton donor, the initial syn-addition product can be trapped, whereas a syn/anti mixture is obtained in a non-protic solvent. This is in sharp contrast to the carbocupration of the same ynone substrate with a cyanocuprate (RCu(CN)Li), which is highly selective for syn-addition. The product selectivities can be understood from a detailed computational characterization of the reaction paths, and in particular from the relative stabilities of the vinyl cuprate and allenolate intermediates. It is suggested that the stereodetermining step is protonation of vinyl cuprate intermediates.     

The development of a facile tandem Wolff/Cope rearrangement for the synthesis of fused carbocyclic skeletons

A set of mild processes for the conversion of vinyl cyclopropyl diazo ketones to highly functionalized cycloheptadienones and vinyl cyclopentenones by use of a target-inspired tandem Wolff/Cope rearrangement sequence is described. A divergent reaction course of the vinyl cyclopropyl diazo ketone substrates under sono- or photochemical activation provides good to excellent yields (55-98%) of the product cycloheptadienones and vinyl cyclopentenones.     

Selective dehydrogenative silylation-hydrogenation reaction of divinyldisiloxane with hydrosilane catalyzed by an iron complex

A hydride and a silyl group of hydrosilane is introduced into 1,3-divinyldisiloxane in the presence of a catalytic amount of (η(5)-C(5)H(5))Fe(CO)(2)Me. Instead of the product expected from the well-known hydrosilylation reaction, the product obtained is that characteristic of dehydrogenative silylation at one vinyl group and hydrogenation at the other vinyl group of 1,3-divinyldisiloxane. Based on deuterium labeling experiments, a catalytic cycle for this new reaction has been proposed.     

Reaction of sulfur with poly(vinyl chloride)

The reaction of elemental sulfur with poly(vinyl chloride) is studied in 1,2,4-trichlorobenzene and without any solvent under various conditions. Black polymers containing 3.77–57.64% chemically bonded sulfur and, according to IR spectroscopy, including >C=C< and >C=S groups in macromolecules are obtained. It is shown that the diffraction curves of poly(vinyl chloride) and of the reaction product containing 7.82% almost coincide but that the thermal stability of the latter is considerably higher than that of the initial polymer. The prospects of the practical use of the products of the reaction of poly(vinyl chloride) with elemental sulfur are demonstrated.     

Specific features of the chemical reaction of carbonyl groups with hydrazine accosting to the data of X-ray photoelectron spectroscopy

The reaction of hydrazine vapor with surface carbonyl groups was used for the quantitative determination of functional groups of organic polymers. The specific features of this reaction were studied using poly(vinyl methyl ketone) as an example. It was shown by X-ray photoelectron spectroscopy that the main reaction product at the initial stage is hydrazinecarbinol, which is then consecutively converted to hydrazone and azine. The results of calculations predict that virtually the only reaction product is azine. It was shown that the wrong identification of the reaction product has lead to the distortion of the results of analysis.     

Synthesis of Hydrophilic-Lypophilic Copolymers in Emulsion: Initiation of Vinyl Chloride by Aqueous Soluble Polymeric Radicals at the Interface

The emulsion polymerization of vinyl chloride initiated by a redox pair in the presence of acrylamide in the aqueous phase gives a product which apparently corresponds to a block copolymer of polyacrylamide and polyvinyl chloride). A reaction scheme is proposed which involves the attack of the vinyl chloride in the micelles by a growing polyacrylamide radical, thus producing the hydrophilic - lypophilic copolymer. Isopropyl alcohol is used as a transfer agent to limit the size of the PAA chains growing in the aqueous phase. The reaction product was characterized by selective solvent extraction, elemental analysis, infrared spectroscopy, and differential thermal analysis.     

5-Exocyclic products, 2,3,5-trisubstituted tetrahydrofurans via Prins-type cyclization

[reaction: see text] 5-Exocyclic products, 2,3,5-trisubstituted tetrahydrofurans, were synthesized from homopropargylic alcohols with terminally substituted alkynes and various aldehydes via Prins-type cyclization. It is of interest that the exocyclic vinyl cation generated as a result of Prins-type cyclization could be trapped as a vinyl triflate when CH2Cl2 was used as a solvent, whereas in ethereal solution the vinyl cation underwent hydrolysis to give the corresponding ketone product.     

Radiation-Induced Addition Reaction of Ethyl Mercaptan and Carbon Tetrachloride to 1,2-Polybutadiene

γ-Ray-induced addition reactions of syndiotactic 1,2-polybuta-diene film with various compounds were carried out at room temperature. The weight of the film markedly increased when ethyl mercaptan was used. In the reaction with ethyl mercaptan, only addition took place without crosslinking. The addition of ethyl mercaptan to the vinyl group of syndiotactic 1,2-poly-butadiene followed anti-Markownikoff rule, and gave a 1:1 addition product. The rate of addition increased as the crys-tallinity of syndiotactic 1,2-polybutadiene used became lower. A similar relation between the crystallinity and the rate of addition was also observed in the γ-ray-induced addition of carbon tetrachloride to syndiotactic 1,2-polybutadiene, but at the same time gelation was pronounced. When liquid 1,2-polybutadiene was used instead of syndiotactic-1,2-polybutadiene, gelation which made the polymer insoluble in carbon tetrachloride did not take place, although a crosslinking reaction was noted. The appearance of the product in this case changed from a viscous liquid to a white powder as the reaction proceeded. The addition of carbon tetrachloride to the vinyl group of liquid 1,2-polybutadiene was also of the anti-Markownikoff type. This addition was accompanied by unexpectedly large vinyl consumption. The total decrease in vinyl group was found to be much larger than the decrease in vinyl group which was brought about by the addition of carbon tetrachloride. This discrepancy was attributed to cyclization and crosslinking reactions which were ascribed to the vinyl group bound by the main chain.     

Total synthesis of formamicin

The enantioselective total synthesis of the cytotoxic plecomacrolide natural product formamicin (1) is described. Key aspects of this synthesis include the efficient transacetalation reactions of MOM ethers 28 and 38 to form the seven-membered formyl acetals 29 and 39, a late-stage Suzuki cross-coupling reaction of the highly functionalized vinyl boronic acid 6 and vinyl iodide 7, a highly beta-selective glycosidation reaction of beta-hydroxy ketone 4 with 2,6-dideoxy-2-iodoglucopyranosyl fluoride 3, and the global desilylation of penultimate intermediate 77 mediated by in situ generated Et(3)N.2HF.     

Rhodium/Silver‐Cocatalyzed Transannulation of N‐Sulfonyl‐1,2,3‐triazoles with Vinyl Azides: Divergent Synthesis of Pyrroles and 2 H‐Pyrazines

The first cyclization reaction between vinyl azides and N‐sulfonyl‐1,2,3‐triazoles is reported. A Rh/Ag binary metal catalyst system proved to be necessary for the successful cyclization. By varying the structure of vinyl azides, such reaction allows the divergent synthesis of pyrroles and 2H‐pyrazines. The cyclization reactions feature a broad substrate scope, good functional group tolerance, high reaction efficiency, and good to high product yields.     

The Mechanism of Reaction between Poly(vinyl Alcohol) and Phosphorous Acid

The reaction mechanism of phosphorous acid and poly(vinyl alcohol) is presented. It has been found that there during this reaction mono- and diesters are formed in which most of the acid radicals are in the phosphonic form. To confirm the presence of this form in the product obtained, reactions with diethyleneamine and chloral have been carried out as characteristic tests for phosphonic groups. The occurrence of C—P bonds resistant to hydrolysis has been also found in the reaction product.     

The first examples of a meta-benzannulation from the reaction of Fischer carbene complexes with alkynes

The intramolecular benzannulations of carbene complexes with alkynes are examined where the alkyne is tethered to the alpha-carbon of the vinyl carbene complex. These reactions are sensitive to the length of the tether and to the nature of the solvent. With a tether length of 16 methylenes, the reaction occurs in the same fashion as the intermolecular reactions to give a p-cyclophane. With intermediate tether lengths (n = 10, 13), the reaction gives an additional p-cyclophane in which the two oxygen substituents are meta on the arene ring. This type of product is unprecedented from the reaction of carbene complexes and alkynes and is quite surprising because the formation of this product requires that the carbon-carbon bond between the alpha- and beta-carbons of the vinyl carbene complex is broken. A mechanism is proposed to account for this process which involves the crossed intramolecular [2 + 2] cycloaddition of the alkene and a ketene in a conjugated dienyl ketene to give a benzvalenone paddalane intermediate.     

Reaction of thioxophosphorane sulfenyl bromides with ethyl vinyl ether: Mechanistic and synthetic aspects

The mechanistic and synthetic aspects of the addition reaction of thioxophosphorane sulfenyl bromide with ethyl vinyl ether were studied in detail by NMR techniques. It has been found that the regiospecific, primary product of the reaction, 1-bromo-1-ethoxy-2S(dialkoxythiophosphoryl)ethane I, is unstable and undergoes slow decomposition to give four compounds. The formation of thiophosphoryl derivatives, vinyl ethers II and III, aldehyde IV, and the symmetrical hemiacetal anhydride V, has been considered in terms of a carbocation intermediate. By choice of the appropriate reaction conditions, the aldehyde IV can be obtained in very high yield.     

Palladium-catalyzed carbene insertion and trapping with carbon nucleophiles

Palladium catalysts are shown to catalyze the three-component coupling of vinyl halides, trimethylsilyldiazomethane, and stabilized carbon nucleophiles. The reaction is believed to proceed through a palladium-carbene intermediate LX(R)PdCHSiMe 3 that undergoes migration of the vinyl substituent to the electrophilic carbene center to generate an eta 3-allylpalladium intermediate. The allylpalladium intermediate is attacked by the carbon nucleophile to generate a vinylsilane product.     

The direct use of phenyldimethylsilanes in silicon assisted palladium catalysed cross coupling

A vinyl-phenylsilane has been used as a masked vinyl organometallic for a cross coupling reaction with phenyl iodide to provide the cine substitution product in high yield.