Donor cyclopropanes in synthesis: utilising silylmethylcyclopropanes to prepare 2,5-disubstituted tetrahydrofurans

The use of donor-only silylmethylcyclopropanes in the Lewis acid promoted reaction with aldehydes to generate 2,5-disubstituted tetrahydrofurans is described. The diastereoselectivity obtained in the product is very much dependent upon the temperature of the reaction.     

Dihalocarbene Addition to Vinylic Selenides-1,1-dihalo-2-(phenylseleno) cyclopropanes

Dihalocarbenes generated under phase transfer conditions add to cis and trans vinylic selenides to give the corresponding 1,1-dihalo-2-selenocyciopropanes with retention of configuration.     

Electrochemical reduction of phenylethynyl halides and related compounds

Reduction of phenylethynyl halides PhCCHal (Hal = I (1), Br (2), Cl (3)), diiodoacetylene (4), (phenylethynyl)triphenylphosphonium bromide (5), and related compounds in THF was studied by means of cyclic voltammetry using a glassy-carbon electrode. Compounds1–5 are reduced with cleavage of the C-Hal bond, and the reduction potentials increase in the order3 <2 <1 <4 <5.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2055–2057, October, 1995.     

Polymerizations of substituted cyclopropanes. I. Radical polymerization of 1,1-disubstituted 2-vinylcyclopropanes

Diethyl 2-vinylcyclopropane-1,1-dicarboxylate (Ia), 2-vinylcyclopropane-1,1-dicarbonitrile (Ib), ethyl 1-cyano-2-vinylcyclopropanecarboxylate (Ic), and 1,1-diphenyl-2-vinylcyclopropane (Id) were radically homo- and copolymerized. Ia, Ib, and Ic polymerized cleanly in 1,5-type ring-opening fashion to yield polymers of high molecular weight. Id failed to homopolymerize but copolymerized with common monomers which included maleic anhydride. Infrared (IR) spectra indicated that the double bonds of the polymer chains were in trans form. All polymers were soluble in solvents and solution-cast films were clear and flexible, showing T_g values in the 25–40°C range. Model reactions of those monomers with benzenethiol also indicated predominant 1,5-addition reactions. From the results of our investigation it was concluded that the driving force for the facile radical 1,5-polymerization of Ia, Ib, and Ic was the stabilization of growing radicals by two substituents.     

Polymerizations of substituted cyclopropanes. II. Anionic polymerization of 1,1-disubstituted 2-vinylcyclopropanes

Among the four 1,1-disubstituted 2-vinylcyclopropanes, diethyl 2-vinylcyclopropane-1,1-dicarboxylate (Ia), 2-vinylcyclopropane-1,1-dicarbonitrile (Ib), ethyl 1-cyano-2-vinylcyclopropanecarboxylate (Ic), and 1,1-diphenyl-2-vinylcyclopropane (Id), Ib and Ic polymerized well with sodium cyanide in N,N-dimethylformamide. Ib was most reactive and a polymer (IIb) from Ib exhibited an inherent viscosity of 1.05 dl/g (concentration of 1.0 g in 100 ml of 95% H₂SO₄). All experimental results indicated that the polymerization proceeded by ring opening and that the structure of the polymers had pendant vinyl groups. The polymer IIc from Ic was soluble in common solvents like acetone, but IIb was soluble only in 95% H₂SO₄. Reactions of those compounds with benzenethiolate ion in ethanol yielded addition products that supported the ring-opening polymerization of those monomers. In the postulated mechanism of polymerization cyanide ion attacks the carbon of a cyclopropane ring with electron-releasing vinyl group and the resulting anion is thereby stabilized by two electron-withdrawing substituents. The propagation takes place by the reaction of the anion with another monomer molecule.     

Organic photochemistry with 6.7eV photons: decomposition of 1,1-disubstituted cyclopropanes in solution

The course of the two-bond cleavage reactions of cyclopropanes in photolysis at 185nm in solution is strikingly influenced by disubstitution of one of the carbons in the ring.     

Calculation of the polymerization process of some 1,1-disubstituted cyclopropanes: the first propagation step

A theoretical study of the first steps of the polymerization propagation process of 1,1 cyano, fluoro and methyl disubstituted cyclopropanes and 1-cyano 1-amino cycloprane is presented. The thermodynamic and kinetic feasibility of the reactions are discussed through 6-31+G(d,p) Hartree–Fock calculations. The anionic initiation and propagation process follows an S_N2 like reaction path mainly governed by the differences in electron affinities between the incoming and outgoing anions, further modulated by the nature of the substituents. Main conclusions are that the π electron-withdrawing groups maintain the barrier heights low, making the process feasible from a kinetic viewpoint. The σ electron-withdrawing groups give more exothermic reactions but their reaction barriers are very high.     

1,1-二卤代-1-烯烃的制备及其在有机合成中的应用

1,1-二卤代-1-烯烃是有机化学中常见的合成片断,在合成化学中已得到了广泛的应用。该综述介绍了这一类化合物常见的制备方法以及反应的适用范围,并详细讨论了该类化合物在有机合成中的应用：(1)1,1-二卤代-1-烯烃在镁、有机锂、锌/溴化亚铜、二碘化钐、零价钯等金属或金属试剂作用下,发生α-消除反应生成烯基卡宾中间体的反应;(2)1,1-二卤代-1-烯烃在合成杂环以及核苷类似物等方面的应用。对于这类化合物在钯催化下的分子内(间)的偶联反应以及利用分子内的双环碳钯化反应,合成环状化合物等等方面的研究进展,也进行了详细的讨论。     

Synthesis of chiral 3,3′-disubstituted 1,1′-binaphthyl-2,2′-disulfonic acids

A convenient synthesis of chiral 3,3′-disubstituted 1,1′-binaphthyl-2,2′-disulfonic acids (BINSA, 1) was developed. The key was directed ortho-lithiation of BINSA methyl ester 2 with n-BuLi and subsequent reaction with an electrophile. Electrophiles such as Br₂, I₂, Me₃SiOTf, and i-PrOB(Pin) reacted smoothly with 3,3′-dilithiated BINSA methyl ester, and the corresponding 3,3′-dihalo-, 3,3′-bis(trimethylsilyl)-, and 3,3′-diboryl-BINSA derivatives were obtained in yields of 21–78%. This simple synthetic method is highly attractive since the ability to prepare 3,3′-disubstituted BINOLs in advance can be useful.     

用碲Ylide合成杂环取代环丙烷衍生物

本文报道了由碲盐和杂环取代查尔酮反应合成杂环取代环丙烷衍生物的简便方法。     

Formal homo-Nazarov and other cyclization reactions of activated cyclopropanes

The Nazarov cyclization of divinyl ketones gives access to cyclopentenones. Replacing one of the vinyl groups by a cyclopropane leads to a formal homo‐Nazarov process for the synthesis of cyclohexenones. In contrast to the Nazarov reaction, the cyclization of vinyl‐cyclopropyl ketones is a stepwise process, often requiring harsh conditions. Herein, we describe two different approaches for further polarization of the three‐membered ring of vinyl‐cyclopropyl ketones to allow the formal homo‐Nazarov reaction under mild catalytic conditions. In the first approach, the introduction of an ester group α to the carbonyl on the cyclopropane gave a more than tenfold increase in reaction rate, allowing us to extend the scope of the reaction to non‐electron‐rich aryl donor substituents in the β position to the carbonyl on the cyclopropane. In this case, a proof of principle for asymmetric induction could be achieved using chiral Lewis acid catalysts. In the second approach, heteroatoms, especially nitrogen, were introduced β to the carbonyl on the cyclopropane. In this case, the reaction was especially successful when the vinyl group was replaced by an indole heterocycle. With a free indole, the formal homo‐Nazarov cyclization on the C3 position of indole was observed using a copper catalyst. In contrast, a new cyclization reaction on the N1 position was observed with Brønsted acid catalysts. Both reactions were applied to the synthesis of natural alkaloids. Preliminary investigations on the rationalization of the observed regioselectivity are also reported.     

Electrochemical oxidation of tetramethylhydrazine, 1,1-dimethyl-2,2-dibenzylhydrazine and tetrabenzyl-hydrazine

Cyclic voltammetric studies of the title hydrazines have shown that the first step of oxidation yields stable radical cations. Though the electron transfer reaction is somewhat slow and very dependent on surface condition when solid electrodes are used, the process is quite reversible at mercury electrodes. Chemical analyses of electrolysis solutions were used to supplement rotating ring-disk voltammetric studies of the second stage of oxidation. The initially formed dication undergoes rapid deprotonation and the protons so formed can react with incoming starting material reducing the currents observed below the two-electron level. Deprotonation of the dication at an α-carbon gives a postulated cationic intermediate which can undergo two reactions whose products were observed: dealkylation to form a hydrazone and deprotonation with N-N cleavage giving an imine.     

Reactions of 2,2-disubstituted 1,1-dicyanoethenes with β-dimethylaminoacrolein aminal and 3-dimethylamino-1,1,3-trimethoxypropane

A reaction of 2,2-disubstituted 1,1-dicyanoethenes with β-dimethylaminoacrolein aminal and 3-dimethylamino-1,1,3-trimethoxypropane leads to substituted 6,6-dicyano-1-dimethyl-aminohexatrienes and an organic salt containing 1,1,9,9-tetracyano-2,8-diphenylnona-2,4,6,8-tetraenide as the anion and (dimethylaminopropenylidene)dimethylammonium as the cation, on the basis of which new cation-anionic polymethine dyes were obtained. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1639–1643, August, 2008.     

Preparation of 1,1-disubstituted silacyclopentadienes

Several new 1,1-disubstituted siloles containing substituents on the ring carbon atoms have been synthesized. The new siloles: 1,1-dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (5), 1,1-dihydrido-2,5-dimethyl-3,4-diphenylsilole (6), 1,1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (7), 1,1-bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (8), 1,1-dipropoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (9), and 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (13) were prepared from reactions originating from the previously reported, 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (1) or 1,1-bis(diethylamino)-2,5-dimethyl-3,4-diphenylsilole (2). In addition, three other new organosilane byproducts were observed and isolated during the current study, bis(4-methoxyphenyl)bis(phenylethynyl)silane (11), bis(4-methoxyphenyl)di(propoxy)silane (12) and 1-bromo-4-bromodi(methoxy)silyl-1,4-bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Compounds 13 and 14 were characterized by X-ray crystallography and 14 is the first 1,1-dibromosilole whose solid state structure has been determined.     

Reactivite dans la serie du methylenecyclopropane—I : Stereochimie de la reduction des dialkyl-1,1 dibromo-2,2 methylene-3 cyclopropanes par un hydrure organostannique

Reduction of dialkyl-gem-dibromomethylenecyclopropanes by organotin hydrides affords a mixture of two isomeric monobromo compounds, whose stereochemistry has been determined. The reaction goes by way of an intermediate methylenecyclopropyl radical and gives, as the major product, that isomer which is formed from the thermodynamically more stable radical.     

Electrochemical and spectral properties of thienylene-polyparaphenylenevinylene derivative stereoisomers

Four new compounds: 1,4-dimetoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene), 1,4-dietoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene), 1,4-isopropyloxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene) and 1,4-dietoksy-2,5-bis[2-(5-methylthiophen-2-yl)ethenyl]benzene are synthesized. Three steroisomers ZZ, EZ and EE are isolated from the reaction mixture for the first two of them. Third compound is fully converted to the most stable EE form. Polymerization of all isomers leads to identical polymeric product. Mechanism of polymerization is recognized by using model molecule with methyl substituents blocking α-, α′-sites. All seven stereoisomers have photoluminescent properties. Detailed spectral and electrochemical studies reveal isomerization phenomena during oxidation or at light exposure. Published in Russian in Elektrekhimiya, 2006, Vol. 42, No. 12, pp. 1401–1408. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes.” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

The reactivity of 2,2"-bipyridine complexes in the electrochemical reduction of organohalides

Nickel(0) complexes coordinatively unsaturated with 2,2"-bipyridine (bpy) are more reactive in the oxidative addition to organic halides than the saturated analogs. -Organonickel complexes formed as intermediates of catalytic cycles were prepared in high yields using nickel complexes coordinatively unsaturated with bpy and aromatic halides containing a methyl group in the ortho-position of the ring.     

Electrochemical reduction of sodium metavanadate in an equimolar KCl-NaCl melt

Electrochemical reduction of sodium metavanadate in an equimolar KCl-NaCl melt and the effect of acid-base properties of environment on this process are studied by a voltammetry method on a stationary platinum electrode. It is established that the limiting current of the NaVO₃ electroreduction process has a kinetic nature. The process proceeds via an autoinhibition scheme and its rate is limited by an acid-base reaction conjugated with an irreversible charge transfer reaction. A substantial role of cationic composition of the melt is revealed experimentally. Following acidification of the KCl-NaCl-NaVO₃ melt by Mg²⁺ (from MgCl₂), the process passes from an irreversible kinetic regime into a reversible diffusion (quasi-diffusion) process. Values of stability constants for vanadates produced with the aid of acid-base titration of vanadium pentoxide by oxygen ions in experimental conditions are presented. These values are taken into account when calculating kinetic parameters of the NaVO₃ electroreduction.