氧杂双环烯烃开环反应的研究及其应用

有机金属试剂(其中包括镍、钯、铑、铁、铜)以及路易斯酸能选择性地催化氧杂双环烯烃的亲核开环反应,并建立多个手性中心。这种方法已经被用在一些生物活性分子的全合成过程当中,如甾体酮类似物等。     

Boron trifluoride promoted reactions of n-haloelectrophiles with alkenes

N-Haloelectrophiles react with alkenes in the presence of boron rifluoride etherate to give halofluorides and N-halo adducts.     

Insertion reactions of alkenes with diterpenoid chromium aminocarbenes

Insertion reactions of electron-deficient alkenes with chromium aminocarbenes derived from podocarpic acid generally give aryl ketone products derived from ring opening of an aminocyclopropane and subsequent enamine hydrolysis, the exception being alkenyl sulphones which give products derived from insertion of the carbene into the β-CH bond of the alkene. Increasing steric hindrance due to the substituents on the aminocarbene nitrogen appears to result in higher yields of the insertion products. However, other factors such as stabilisation of the intermediate tetracarbonylaminocarbene may explain why morpholinocarbenes give superior yields of the insertion products. Propenoic acid, propenal or nitropropene give a 13-formyl-substituted diterpenoid. Electron-rich alkenes do not undergo insertion reactions with these aminocarbenes at 110°C.     

Acid catalyzed ring closure reactions of electrophilic alkenes

Treatment of -acyl-,β-unsaturated ketones with sulfuric acid or dimethylformamide-hydrogen chloride or p-toluenesulfonic acid gave rise to 3-acyl-2-alkyl-4,5-dihydrofurans. Similar cyclization of -acyl-,β-unsaturated esters initially afforded 3-alkoxycarbonyl-2-alkyl-4,5-dihydrofurans which were transformed into 2-acylbutanolides on further reaction with sulfuric acid.

This acid catalyzed cyclization is strongly dependent upon the substitution pattern of the electrophilic alkenes, the acid used and reaction conditions.     

Coupling reactions of zirconocene complexes and heterosubstituted alkenes

This tutorial review surveys recent advances in the field of zirconium promoted coupling reactions of unsaturated molecules (and/or organolithium compounds) and heterosubstituted alkenes. This reaction has recently emerged as a powerful tool in organic chemistry to access a variety of synthetically useful building blocks not easily available by other methods. In particular, three different reaction pathways are discussed: i) the reaction involving alkyne-zirconocene and aryne-zirconocene complexes which allows access to dienyl and aryl zirconocene complexes; ii) the reaction of alkene-zirconocene complexes and enol ethers which has shown to be highly dependent on the structure of the enol ether used, allowing the synthesis of simple vinyl zirconocenes or multicomponent coupling products, and; iii) the reaction involving imine-zirconocene complexes which supposes a new entry to allylic amines.     

Synthesis of bridged 1,4-diazepane derivatives via Schmidt reactions

A series of bridged 1,4-diazepanes (i.e., diazabicyclo[n.3.2]alkanes, n = 3-5) selectively protected at one of the nitrogen atoms was prepared, for possible application in drug design, via Schmidt rearrangement of the corresponding ketones.     

(2-Chlorovinyl)chlorocarbenes: Generation and reactions with alkenes

The treatment of Z-1,1,3-trichloro-4,4-dimethyl-2-pentene (Ia) with t-C₄H₉OK in boiling hexane or benzene gave rise to (Z-2-chloro-3,3-dimethyl-1-butenyl)chlorocarbene (IVa), which reacted with alkenes to give the cyclopropane derivatives (V) in 44–57% yields. Dichloro-(2-chloro-1-alkenyl)methanes (Ib-d), which have a hydrogen atom at the C₃ position of the alkenyl substituent, were also used as carbene precursors under these conditions. These compounds gave rise to mixtures of the cyclopropanes (VI)–(VIII) (obtained in up to 57% yields) and the dienes (IX)–(XI) (yields up to 54%). The reaction of cis-2-butene with (2-chloro-1-cyclopentenyl)chlorocarbene (IVd) was found to be completely stereospecific, indicating that this carbene exists in a singlet ground state.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2552–2558, November, 1991.     

Modelling carbocationic polymerizations: Kinetics of the reactions of carbocations with alkenes

Reactions of carbocations with olefins and related π-nucleophiles follow second order kinetics, first order with respect to carbocation and first order with respect to olefin. The rate constants are equal for paired and non-paired ions and independent of the nature of the negative counter-ions. Rate constants k < 10⁷-10⁸ L mol⁻¹ s⁻¹ can be calculated by lg k(20 °C) = s (N+E), where E represents the strengths of the electrophiles, while nucleophiles are characterized by the slope parameter s and the nucleophilicity parameter N. These parameters can be used for selecting initiators for carbocationic polymerizations and for designing copolymers.     

Rate constants for reactions of perfluorobutylperoxyl radical with alkenes

Perfluorobutylperoxyl radicals were produced by radiolytic reduction of perfluorobutyl iodide in aerated methanol solutions. Rate constants for the reactions of this peroxyl radical with various organic compounds were determined by kinetic spectrophotometric pulse radiolysis. The rate constants for alkanes and alkenes were determined by competition kinetics using chlorpromazine as a reference. The results indicate that hydrogen abstraction from aliphatic compounds takes place with a rate constant that is too slow to measure in our system (<10⁵ M^?1 s^?1), and that abstraction of allylic and doubly allylic hydrogens is slow compared with addition. Addition to alkenes takes place with rate constants of the order of k = 10⁶ ? 10⁸ M^?1 s^?1. Good correlation was obtained between log k and the Taft substituent constants σ* for the various substituents on the double bond. Perfluorobutylperoxyl radical is found to be more reactive than trichloromethylperoxyl and other peroxyl radicals.     

Termination reactions in the metathesis polymerization of cyclic alkenes

A kinetic study of the polymerization of cyclopentene initiated by the metathesis catalyst WCl₆/AliBu₃ has shown the presence of termination reactions The termination processes (probably there are more than one), are second order in nature and also result in the reduction of the oxidation state of the transition metal. Reactivation of the transition metal complex towards metathesis polymerization can be effected by the addition of oxygen to a dead system.     

Exchange reactions in the living cationic polymerization of alkenes

Living cationic polymerization of alkenes is discussed in terms of rapid dynamic equilibration between carbenium ions and either covalent species or onium ions. Rates of exchange between these species have strong effect on polydispersities of the synthesized polymers. In the discussed living systems, rates of exchange are faster than rates of propagation. Propagation proceeds via classic carbocationic mechanism.     

Novel amine-catalysed hydroalkoxylation reactions of activated alkenes and alkynes

Substoichiometric loadings of DBU catalyse the efficient 1,4-addition of alcohols and non-nucleophilic amines such as pyrrole to activated alkenes; the application of this methodology in a one-pot synthesis of a natural product, and as a novel strategy for the synthesis of mono-protected 1,3-carbonyl compounds is reported.     

Ritter-type reactions of N-chlorosaccharin: a method for the electrophilic diamination of alkenes

[reaction: see text] N-Chlorosaccharin has been shown to undergo electrophilic Ritter-type reactions with alkenes in acetonitrile. The resulting labile beta-chloro sulfonylamidines can be ring-opened and cyclized to imidazolines. Overall this provides a one pot method for the electrophilic diamination of alkenes. Competing aziridine formation as well as allylic chlorination are also observed depending on the nature of the alkene used.     

Intermolecular hydroamination and hydroarylation reactions of alkenes in ionic liquids

Intermolecular hydroamination or hydroarylation reactions of norbornene and cyclohexadiene performed with catalytic amounts of Brönsted or Lewis acid in ionic liquids were found to provide higher selectivity and yields than those performed in classical organic solvents. The ionic liquid increases the acidity of the media and stabilizes ionic intermediates through the formation of supramolecular aggregates.     

Multifaceted palladium catalysts towards the tandem diboration-arylation reactions of alkenes

Novel Pd(2) (6+) compounds have been synthesized in high yield. These compounds and their Pd(2) (4+) counterparts as synthetic precursors mediate the diboration of vinylarenes and aliphatic 1-alkenes, and under mild and basic reaction conditions they produce a variety of 1,2-diboronate esters with excellent conversions and chemoselectivities. The presence of bis(catecholato)diboron (B(2)cat(2)) favours the reduction of Pd(III) to Pd(II), while the catalytic precursor of Pd(II) is transformed into Pd(0)-nanoparticles. An "in situ" catalytic tandem reaction has been designed to transform the diboronate intermediates into the monoarylated product, which after oxidative workup, provides the carbohydroxylated adduct. Eventually, the same catalyst performs both sequences with total conversion from the alkene.     

Catalytic amination of unsaturated hydrocarbons: reactions of p-nitrophenylazide with alkenes catalysed by metallo-porphyrins

Porphyrin derivatives of transition metals such as Ru(TPP)CO, Ru(OEP)CO and Co(OEP)(TPP=dianion of 5, 10, 15, 20-tetraphenylporphyrin, OEP=dianion of 2, 3, 7, 8, 12, 13, 17, 18-octaetylporphyrin) catalyse the reaction of p-nitrophenylazide with cyclohexene to give the corresponding allylamine in good yields. With other olefins such as cyclooctene, 1-octene, styrene and substituted styrenes the main product becomes the corresponding aziridine. The reaction of p-nitrophenylazide with Ru(TPP)CO has been investigated and the mechanism of the catalytic reactions is discussed.