Benzyl bromide vinyl substitutions

Normally, the most practical vinyl substitutions are achieved by use of the oxidative additions of organic bromides, iodides, diazonium salts or triflates to palladium(0)-phosphine complexes in situ. The organic halide, diazonium salt or triflate, an alkene, a base to neutralize the acid formed and a catalytic amount of a palladium(II) salt, usually in conjunction with a triarylphosphine, are the usual reactants at about 25-100 C. This method is useful for reactions of aryl, heterocyclic and vinyl derviatives. Acid chlorides also react, usually yielding decarbonylated products, although there are a few exceptions. Likewise, arylsulfonyl chlorides lose sulfur dioxide and form arylated alkenes. Aryl chlorides have been reacted successfully in a few instances but only with the most reactive alkenes and usually under more vigorous conditions. Benzyl iodide, bromide and chloride will benzylate alkenes but other alkyl halides generally do not alkylate alkenes by this procedure. 

Like other acid chlorides and cyanogen bromide, vinyl chloroformate brings about fission of benzylic and allylic amines e.g. hydrastine is converted into the enol lactone (145).169 Normorphine and norcodeine give substituted thioureas (146) with alkyl isothiocyanates.170... 

Pd(Ph3P)4 catalyzes the carbonylation of benzyl and vinyl bromides under phase transfer conditions in the presence of hydroxide to form the corresponding carboxyhc acids. A wide variety of substitution is tolerated and the products are formed in moderate to excellent yield at room temperature and at normal pressure (1 atm CO). Extension of the reaction to the formation of esters from aryl, alkyl, and vinyl bromides has been described. These transformations usually require a co-catalyst system of Pd(Ph3P)4 and [(l,5-cyclohexadiene)RhCl]2 in the presence of either M(OR)4 (M=Ti, Zr) or M(OR)3 (M=B, Al) (eq 22). 

Nucleophilic Substitutions of Halides. Although unreactive with benzyl bromide and vinyl iodides, lithium (3,3-diethoxy-l-propen-2-yl)(phenylthlo)cuprate undergoes clean substitutions with allyllc bromides to afford 1,4-dienes (eq 1). The mixed homocuprate lithium (3,3-diethoxy-l-propen-2-yl)(3,3-dlmethyl-l-bulynyl)cuprate provides similar results. ... 

TMS-alkynes are oxidized at the terminal carbon to carboxylic acids by hydroboration/oxidation (dicyclohexylborane/NaOH, H2O2). This does not work with TIPS-alkynes. Instead, TIPS-alkynes are cleanly monohydroborated at the internal carbon by 9-borabicyclo[3.3.1]nonane dimer to give (Z)- -borylvinyl-silanes. These can be oxidized in high yields to a-silyl ketones, or cross coupled with a bromide R Br (R = aryl, benzyl, dimethyl-vinyl) in the presence of NaOH and tetrakis(triphenylphos-phine)palladium(0) to give /3,/3-disubstituted vinylsilanes (Suzuki reaction eq 14). The same nucleophilic substituted vinylsilane can be added to an aromatic aldehyde to provide access to ( )-3-silyl allyl alcohols. ... 

Organometallics are formed at the cathode if transient radicals produced in reductions react with the active electrode. This occurs as a side reaction in cathodic coupling (Sect. 12.2, Eq. (185)) of carbonyl compounds, e.g., of acetone 3 9 or of activated olefins, e.g., of methyl vinyl ketone 41or acrylonitrile. Furthermore, in cathodic cleavage (Sect. 13.2, Eq. (227) ) of alkyl bromides or iodides organometallics are formed, e.g., ME(CH2CH2CN)2(ME = Pb, Tl, Sn, Hg) 481 bis(p-substituted benzyl)mercury 485 or dicyclopropylmercury 489 ... 

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