Elimination of alkyl groups

Lithium hydride reacts completely with 9-BBN and ThxBHj at room temperature after 48 h (Eq. 22.1), whereas ChXjBH, SiajBH, and IPC BH remain inert. In addition, the reactions of 9-BBN and ThxBHj in THE under reflux condition are completed in 3 h. However, the other organoboranes at reflux undergo rapid redistribution and/or elimination of alkyl group. 

Addition of triphenylphosphine retards the decomposition. Analysis of the products reveals that the three-co-ordinate intermediate maintains sufficient stereochemical integrity to allow cis elimination of alkyl groups. ... 

Ease of elimination of alkyl groups is in the order methyl > n-propyl > ethyl, and electron-withdrawing groups substituted in the aromatic ring increase the rate of displacement. 

Dealcoholation 16, 945 Dealkylation (s. a. Elimination of alkyl groups. Monodealkylation)... 

Also obtained during the particular Fries rearrangements of some aryl esters during which there is usually an elimination of alkyl group,... 

Carboxylic acids from lactones with elimination of alkyl groups s. 11, 790 n-Octanoic anhydride (n-C H gCO)20... 

Dealkylation (s. a. Elimination of alkyl groups. Monodealkylation, Replacement of alkyl groups by hydrogen) G-Dealkylation, quinoline ring with — 12, 948 N-Dealkylation (s. a. N-De-methylation) 14, 50, 54, 769 0-Dealkylation (s. a. Ethers, cleavage)... 

IV-Methylated pyridazinones can be obtained from 3,6-dialkoxypyridazines by treatment with alkyl halides or dialkyl sulfates. Methyl iodide and dimethyl sulfate are most frequently used. According to the proposed mechanism, an intermediate quaternary pyridazinium salt is formed, followed by elimination of a group R from the alkoxy group. At higher temperature, l,2-dimethylpyridazine-3,6(l//,2//)-dione is formed with dimethyl sulfate. 

Elimination bimolecular (E2) mechanism (Section 5.15) Mechanism for elimination of alkyl halides characterized by a transition state in which the attacking base removes a proton at the same time that the bond to the halide leaving group is broken. 

Michael acceptors and 1,4-addiiion of alkyl group is a normal process. The reaction mechanism is not clear, but the process via addition of alkyl radicals and subsequent elimination of NO radical is one of the possible routes. Recently, several related reactions have been reported, as shown in Eq. 4.76, Eq. 4.77, and Eq. 4.78, in which alkyl radicals are involved. The reaction of trialky Igalliiim compounds with nitrostyrene gives also a similar snbsdtiidon product fEq. 4.791. ° ... 

These A -acyl phosphazenes also decompose further on heating to PhaMePO and RCN. The elimination of methyl iodide probably occurs by a course closely related to the elimination of alkyl halides in the Arbusov reaction, where the alkoxy-group undergoes nucleophilic attack by halide ion. 

In all of these cases, paUadium-catalyzed hydrosilylation proceeds via hydropalla-dation followed by reductive elimination of alkyl- and silyl group from the palladium. In the reaction of o-aUylstyrene (24) with trichlorosilane, which gives hydrosilylation products on the styrene double bond 25 and cycUzed product 26, the hy-dropalladation process is supported by the absence of side products which would result from the intermediate of the silylpaUadation process (Scheme 3-11) [37]. 

Alkyl substituents on boron in 9-BBN derivatives can be coupled with either vinyl or aryl halides through Pd catalysts.22413 This is an especially interesting reaction because of its ability to effect coupling of saturated alkyl groups. Palladium-catalyzed couplings of alkyl groups by most other methods often fail because of the tendency for (3-elimination... 

SRN I reactions using related p-nitrophenyl or p-nitrocumyl systems41 as reductive alkylating agents have been studied by Komblum and co-workers these are well summarized in the reviews.39 At the same time, Russell discovered the S l reaction of geminal halonitroalkanes with stabilized carbanions (see Eq. 5.25).42 The products are readily converted into alkenes via elimination of nitro groups (see Section 7.3). 

Much evidence supports the conclusion that the elimination of the group HX from alkyl halides by bases is a trans elimination reaction. This means that the atoms H and X leave from the opposite site of the incipient double bond. It is mostly explained by assuming that the electrons which are left by the leaving proton and which will form the double bond prefer to attack the leaving group X from the rear (50). The transition state for the elimination, if it is concerted, is most stable if H, X, and the carbon atoms 1 and 2 lie on one plane, which in most molecules is best realized in the trans position (51). ... 

The combination of the photopromoted carbotelluration with the elimination reaction, provides a useful method for the introduction of alkyl groups to terminal acetylenes. 

The mechanism of this elimination reaction may be regarded as being similar to that of the dehydrogenation reaction. Double-bond isomerization leads to formation of a species with both double bonds in the ring. This is then metalated and eliminates the alkyl group (A )-... 

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