Chain with vinyl halides

Dihydroquinolines can be synthesized by the palladium-catalyzed reaction of o-allyl- or o-isoprenyl-iV-tosylanilides with vinyl halides or triflates (Equation 135) <1998TL1885, 1998TL2515, 1998T9961, 1998TL2965, 1998JOC4554>. By-products can be formed in the instance of n-vinylanilide, including indoles and extended chains. 

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

Four-carbon-chain extensions have been very successful with conjugated dienes as the functionalized olefins. We have used a few other compounds also, but they are of limited value, such as N-3-butenylphthalimide. The last compound is only useful with aromatic or certain vinyl halides where mixtures of allylic amines would not be formed. A typical diene example is the reaction of vinyl bromide with butadiene and piperidine which gives E-N-(2,5-hexadienyl)-piper-idine in 70% yield (7). The product of this reaction can be reacted again and used to extend the carbon chains by six atoms (see below). The reactions of conjugated dienes can be used to produce conjugated trienes also (4). 

Five-carbon-atom-chain extensions have been achieved with three kinds of unsaturated compounds 1,4-dienes, 2,4-dienoic acids or esters, and N-2,4-dienylamines. The 1,4-dienes are generally useful with aromatic halides, but give mixtures of isomeric amines with most vinylic halides because of elimination and readdition of palladium hydride in both possible directions to produce two different 7r-allylic intermediates. Exceptions occur in cases where symmetrical compounds are being formed and where both directions of elimination lead to the same product (8). For example ... 

Hydrogen halide addition to vinyl chloride in general yields the 1,1-adduct (50—52). The reactions of HQ and hydrogen iodide [10034-85-2], HI, with vinyl chloride proceed by an ionic mechanism, while the addition of hydrogen bromide [10035-10-6], HBr, involves a chain reaction in which a bromine atom [10097-32-2] is the chain carrier (52). In the absence of a transition-metal catalyst or antioxidants, HBr forms the 1,2-adduct with vinyl chloride (52). HF reacts with vinyl chloride in the presence of stannic chloride [7646-78-8], SnQ4, to form 1,1-difluoroethane [75-37-6] (53). 

RMeiSiCH diunion equivalent. The reagents are obtained from RMe SiCHBr by treatment with Zn/Pb in THF at 60°. They react with vinylic and allylic halides and can be used in chain stitching processes. 

The reactions are accelerated by radical initiators or by UV light, and inhibited by radical scavengers,128-129 and, under suitable conditions, the reaction of stannyl radicals with alkyl halides to give the corresponding alkyl radicals can be observed by ESR spectroscopy.130 Optically active alkyl halides react with racemisation,129 but vinyl halides may show some retention of configuration at low temperature. The reactions are therefore accepted to follow the radical chain mechanism which is depicted in Scheme 15-2. 

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