Hydrocarbons, hydrocarbon ethers, cleavage

Like //-butyUithium, j iZ-butyUithium is infinitely soluble in most hydrocarbons, such as pentane and hexane. Its solutions in hexane are flammable and pyrophoric and therefore should be handled like //-butyUithium (96,100). j iZ-ButyUithium also is very soluble in ethers, but the ether solutions must be kept cold because ether cleavage is more rapid than in the presence of //—butyUithium (122). j iZ-ButyUithium has a t 2 of 2 d at 25°C in di-//-butyl ether and of 1 d at 25°C in di-//-hexyl ether. 

In general, the electron donor substrate is oxidized by PET to a cation-radical which undergoes C—C bond cleavage to form the most stable radical and cation pair. These species react further with solvent and with the reduced A to form hydrocarbon and ether products [41]. Griffin [42], Albini [43a], and Kochi [43b] have also contributed significantly to this research area. 

The R3AI can be substituted by R Li or R MgX, although the yields are lower (borate formation, ether cleavage). Moderate yields of cyclic triorganoboranes R2BR are obtained from the reaction between R BX2 (X = F, Cl) and dimetallated hydrocarbons (M = Li, MgX) ... 

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

The mass spectra of TMS ethers are characterized by weak or absent molecular ions the [M-15] ion formed by cleavage of a methyl to silicon bond is generally more abundant. This ion can be used to determine the molecular weight provided that it is not mistaken for the molecular ion itself. Dissociation of the molecular ion often results in prominent secondary fragment ions containing the ionized dimethylsiloxy group attached to a hydrocarbon portion of the molecule. In common with alkyl ethers,... 

A commonly used and important reaction of sulfonic acids, or sulfonates, is their conversion to sulfonyl chlorides by treatment with phosphorus halides, or sometimes with thionyl chloride. Although it is easy to postulate mechanisms for this conversion, the exact path followed has never been determined. Similarly, although mechanisms can be suggested for other known reactions involving sulfonic acids, such as the cleavage of dialkyl ethers by anhydrous sulfonic acids (Klamann and Weyerstahl, 1965), or the formation of sulfones by treatment of an aromatic hydrocarbon with a mixture of sulfonic acid plus polyphosphoric acid (Graybill, 1967), nothing truly definitive is known about the details of the actual mechanisms of these reactions. 

For many years, intramolecular reactions such as conformational changes, bond cleavage, bond formation, and valence isomerizations have been observed only when hydrocarbons were reduced with alkali metals in ethereal solvents. In most electrochemical experiments, these reactions were dominated by the electrophilic processes already described. However, progress in experimental techniques [8, 9, 27-29] has made these reactions accessible to electroanalytical investigations, providing new mechanistic insight. 

Electrochemical fluorination in anhydrous hydrogen fluoride (Simons process) involves electrolysis of organic compounds (ahphatic hydrocarbons, haloalkanes, acid halides, esters, ethers, amines) at nickel electrodes. It leads mostly to perfluori-nated compounds, but is accompanied to a high extent by cleavage and rearrangement reactions. The mechanism of the formation of carbocations according to Eq. (1) and Scheme 1 is assumed... 

Electroreduction of esters (R COOR ) is classified into three types of reaction. The first type of reaction is the reductive cleavage of a bond between oxygen and R. This type of reaction is similar to the cathodic reduction of alcohols (Sect. 7.2) and ethers (Sect. 7.3). That is, activated esters such as allylic and benzylic esters are electrochemically reduced to the corresponding hydrocarbons and acids (Schemes) [1,16,19-21]. 

The intensity of the molecular ion of aliphatic amines decreases regularly with increasing molecular weight. [33] Analogous general behavior has also early been noted for other compound types such as the aliphatic ethers [31], hydrocarbons [34] and aldehydes [24], and others. The reason for the low stability of amine molecular ions is their predisposition to a-cleavage. 

Other procedures include zinc-dust distillation, not generally useful except for exhaustive degradation of phenols to hydrocarbons, and various sodium and liquid ammonia cleavages of phenol ethers.3-7 These latter reactions lack generality and are often unpredictable. They require conditions too harsh for... 

The desulfurization of 1,4-oxathiane with sodium in refluxing hydrocarbon solvent, which allows the formation of diethyl ether in very good yield (>95%), can be reported here <1998TL2671>. Furthermore, 6-hydroxy-1,4-benzodithiin undergoes a reductive cleavage with lithium in liquid ammonia, provided the 3,4-dimercaptophenol <2004BML3753>. 

However, this intramolecular cycloadditiou methodology has found more widespread use in the preparation of cis-fused heterobicychc rather than carbobicyclic products, by insertion of a heteroatom into the hydrocarbon tail of the alkenyl nitrone. Particular attention has been given to the synthesis of THF adducts (326, X = 0) (202,317,354,358-365), and to a lesser extent the N (82,361,366-368) S (202,203,369), or silyloxy analogues (54,55,370). Aurich and Biesemeier (359) prepared ether dipoles (327), which slowly cyclized at ambient temperature to afford the cis-fused bicyclic adducts 328 (Scheme 1.70). Reductive cleavage of the... 

As with long-chain ethers, the hydrocarbon pattern may dominate the spectrum of long-chain sulfides the CnH2n peaks seem especially prominent. In branched-chain sulfides, cleavage at the branch may reduce the relative intensity of the characteristic sulfide peaks. 

The results of the Wurtz-like reaction depend on the reaction conditions. An important factor is the kind of solvent The ethers are generally better than hydrocarbons, but with the cyclic ethers like tetrahydrofuran (THF), dioxane and other frequently used agents, a cleavage reaction of the ethers was observed392. Hexamethylphosphoricacid amide was recently used with good results in combination with lithium497. ... 

C—O bond cleavage with the charge remaining on the alkyl fragment. The spectrum of long-chain ethers becomes dominated by the hydrocarbon pattern. 

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