Allyl halides chain transfer

It is often difficult to make a comparison between the various results obtained for the same polyenes as different reaction conditions (ratio of reactants, temperature, time) were used in each case. The addition of dichlorocarbene (chloroform/base/phase-transfer catalysis) to straight chain and cyclic unconjugated di- and trienes, carried out under identical conditions but varying the catalysts, showed the peculiar properties of tetramethylammonium chloride. Under precisely tailored conditions, either highly selective mono- or polyaddition of dichlorocarbene to the polyenes is possible tetramethylammonium chloride was the most efficient catalyst for monocyclopropanation. (For the unusual properties of tetramethylammonium salts on the phase-transfer catalyzed reaction of chloroform with electrophilic alkenes see Section 1.2.1.4.2.1.8.2. and likewise for the reaction of bromoform with allylic halides, see Section 1.2.1.4.3.1.5.1.). For example, cyclopropanation of 2 with various phase-transfer catalysts to give mixtures of 3, 4, and 5, ° of 6 to give 7 and 8, ° and of 9 to give 10 and 11. °... 

For example, direct treatment of red phosphorus with potassium hydroxide in a mixture of dioxane and water with a phase-transfer catalyst (benzyltriethylammonium chloride) allows direct reaction with primary haloalkanes to form the trialkylphosphine oxide in moderate (60-65%) yield.1415 Allylic and benzylic halides are similarly reported to generate the corresponding tertiary phosphine oxides. When the reaction is performed with a,(o-dihalides, cyclic products are generated only with four- and five-carbon chains the third site... 

By far the most generally useful synthetic application of allyltributyltin is in the complementary set of transition metal- and radical-mediated substitution reactions. When the halide substrates are benzylic, allylic, aromatic or acyl, transition metal catalysis is usually the method of choice for allyl transfer from tin to carbon. When the halide (or halide equivalent) substrate is aliphatic or alicyclic, radical chain conditions are appropriate, as g-hydrogen elimination is generally not a problem in these cases. 

Sodium salts of carboxylic acids, including hindered acids such as mesitoic, rapidly react with primary and secondary bromides and iodides at room temperature in dipolar aprotic solvents, especially HMPA, to give high yields of carboxylic esters.679 The mechanism is Sn2. Another method uses phase transfer catalysis.680 With this method good yields of esters have been obtained from primary, secondary, benzylic, allylic, and phenacyl halides.681 In another procedure, which is applicable to long-chain primary halides, the dry carboxylate salt and the halide, impregnated on alumina as a solid support, are subjected to irradiation by microwaves in a commercial microwave oven.682 In still another method, carboxylic acids... 

Silyl group transfer can also be used to functionalize chain ends. For example, allyl silanes, silyl ketene acetals, and silyl enol ethers [301-304] generate polymers with terminal allyl and methacrylate groups [Eq. (103)]. This type of transfer becomes degradative (termination) if reinitiation with silyl halides is not possible. 

With these catalysts molecular weights would, in the absence of chain termination reactions, increase directly with conversion, with Poisson distributions. Monomer transfer, which has been observed with the 7r-allyl nickel halide catalysts, would lead to lower values and a broadening of the distribution. 

Monoaddition of 1,3-butadiene followed by instantaneous halide transfer from the counteranion and selective formation of the trans-1,4-adduct (PIB-allyl-X) was observed in Hex/MeCl 60/40 [viv) solvent mixtures at -80 °C at [1,3-butadiene] 0.05 mol 1" ([1,3-butadiene]/[chain... 

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