Multiple bond systems

Addition Reactions across Polyfluoroalkyl- and Perfluoro-aUcyl-Substituted CO and CN Multiple Bond Systems... 

Cyclocondensation reactions with perfluoroalkyl-subsbtuted CO and CN multiple bond systems can be divided into several subgroups, according to the charge pattern of both reactants On the basis of this simple concept, hetero-l,3-dienes should undergo two types of condensation reactions, classified by the number of skeleton atoms of the diene being incorporated into the ring system (equation 10). 

Perfluoroalkyl groups adjacent to multiple bond systems lower the frontier molecular orbitals (FMOs) Therefore, cycloaddition reactions preferentially occur with electron-rich multiple-bond systems The preference of bis(trifluoromethyl)-substituted hetero-l,3-dienes for polar reacuons makes them excellent model compounds for developing new types of diene reactions deviating from the well documented Diels-Alder scheme (pathway 1) A systematic study of the reactions of diene (1 =2-3=4)-dienophile (5=6) combinations reveals new synthetic possibilities that have not yet been fully exploited as tools for preparative organic cherrustry (equation 25)... 

Perfluorinated and partially fluorinated substituents directly bonded to hetero multiple bond systems lower the energies of FMOs Consequently, they are highly reactive in H0MO (l,3-dipole)-LUMO (dipolarophile)-controlled [3+2] cycload-... 

The above cycloaddition process consists of two separate [3-1-2] cycloaddition steps and represents a 1,3-2,4 addition of a multiple bond system to a hetero-1,3-diene [7S7]. The structure ot the azomethine imine intermediate has been proved unequivocally by X-ray analysis [195] Ethylene [194], acetylene [/iS2] . many alkyl- and aryl- as well sgemmal dialkyl- and diaryl-substituted alkenes [196,197, 198, 199], dienes [200], and alkynes [182, 201], certain cyclic alkenes [198, 199,... 

Bis(trifluoromethyl)-substituted heterodienes are electron-deficient species They therefore react preferentially with electron-rich multiple bond systems to give [4+2] cycloadducts (Diels-Alder reaction with inverse electron demand) [238]... 

On the other hand these are compounds with marked 1,4-dipolar character, having electron lone pairs at the terminal heteroatom and an electrophilic center at C-4 Consequently, they can react with polarized multiple bond systems, even when these are extremely electron-poor [225]... 

The reactions of bis(trifluoromethyl)-subsatuted hetero 1,3 dienes are predomi nantly LLJMO controlled processes [238] With polar or highly polarizable dieno philes, the tendency to undergo stepwise cycloaddition reactions is considerable Notably these hetero-1,3-dienes react with a,(l unsaturated hetero multiple bond systems across the hetero multiple bond exclusively [243, 246 248] (equation 53)... 

In contrast, when ot,P-unsaturated multiple bond systems act as dienophiles in concerted [4+2] cycloaddition reactions, they react across the C=C double bond Periselectivity as well as regiochemistry are explained on the basis of the size of the orbital coefficients and the resonance integrals [25S]... 

Org. Chem. 1978, 43, 4207-4215 a related azepine formation through addition of N-unsubstituted azidirines to electrophilic carbon-carbon multiple bond systems such as acrylonitrile followed by aza-[3,3]-Claisen rearrangement was reported by Hassner (c) A. Hassner, R. D Costa,... 

The fourth chapter gives a comprehensive review about catalyzed hydroamina-tions of carbon carbon multiple bond systems from the beginning of this century to the state-of-the-art today. As was mentioned above, the direct - and whenever possible stereoselective - addition of amines to unsaturated hydrocarbons is one of the shortest routes to produce (chiral) amines. Provided that a catalyst of sufficient activity and stabihty can be found, this heterofunctionalization reaction could compete with classical substitution chemistry and is of high industrial interest. As the authors J. J. Bmnet and D. Neibecker show in their contribution, almost any transition metal salt has been subjected to this reaction and numerous reaction conditions were tested. However, although considerable progress has been made and enantios-electivites of 95% could be reached, all catalytic systems known to date suffer from low activity (TOP < 500 h ) or/and low stability. The most effective systems are represented by some iridium phosphine or cyclopentadienyl samarium complexes. 

Compounds of multiple bond systems involving heavier main group elements were long considered to be unstable and synthetically inaccessible. In particular, the so-called double bond rule, which forbade the formation of (pn-pn) multiple bonds between silicon and other elements, hindered the development of the chemistry of low-coordinate silicon compounds containing Si=X (X = C, N, Si, P) double bonds for some years. 

A similar inference about the importance of the metal can be drawn from the differences in behavior with carbon-nitrogen multiple bond systems m... 

As far as substrates are concerned, while the usual 1,4-addition and 1,3-substi-tution (Sn2 ) reactions of simple unsaturated substrates have so far predominated, analogous transformations of ambident substrates with extended multiple bond systems (i.e., with two or more reactive positions) have come to attention only recently. Here, systematic investigations have shown that such 1,5-substitutions and even 1,6- and 1,8-addition reactions proceed highly regioselectively and ste-reoselectively, in particular when the substrate contains at least one triple bond besides one or more conjugated double bonds. These unusual reaction types not... 

In spite of the general ambiphilicity of phosphonio-substituted phosphoHde derivatives, the aromaticity of the phosphoHde ring [10, 11] tends to reduce their electrophilicity while the intramolecular compensation of the negative charge by the phosphonio-substituents lowers at the same time their nucle-ophilicity [15, 16]. Bis-phosphonio-benzophospholides and -1,2,4-diaza-phospholides are therefore less reactive towards electrophiles and nucleophiles than other types of phosphorus containing multiple-bond systems and lack the notorious hydrolytic instabihty of many of these species [15, 16, 24]. Reactions are observed, however, with sufficiently strong electrophiles such as triflic acid or methyl triflate, or nucleophiles such as OH" or lithium alkyls, respectively. 

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