Metal catalysed alkene addition reactions in organic synthesis

Lewandowska, Krystyna (1989) Metal catalysed alkene addition reactions in organic synthesis. (PhD thesis), Kingston Polytechnic, .


The reaction between [CO[sub]2(CO)[sub]8] and CC1[sub]4 has previously been reported to lead to the formation of dichlorocarbene.ln the presence of cyclohexene,the carbene was reported to add to the alkene giving 7,7-dichlorobicyclo[4.1.0]heptane. This reaction has been reinvestigated and it has been shown that the principal pathway involves formation of CC1 [sub]3 radicals, which react with cyclohexene to farm almost equal proportions of twa isomers of 1-chloro-2- (trichloromethyl)cyclohexene (adduct).Carbene formation has been shown tobe only a minor pathway. A mechanism has been præposed which accounts far these findings. The addition of CC1[sub]4 to cyclohexene in the presence of a range of metal complexes has been studied. Use of ather dinuclear metal carbonyls gave a higher yield of the adduct than observed with [C0[sub]2(CO[sub]8)].The reactions were also more stereoselective. [RuC1[sub]2(PPh[sub]3)3], [RuH[sub]2(PPh[sub]3)4] and [RuH[sub]3(SiPhMe[sub]2) (PPh[sub]3)3] all gave much higher yields and has been suggested this is a consequence of a metal complex catalysed reaction mechanism in which radical pair formation plays an important role. The three ruthenium complexes appear to generate the same active catalytic species. The effect of variation of the phosphine ligand has been studied using [RuC1[sub]2{(4-X-C[sub]6H[sub]4)[sub]3P}[sub]3] (where X=C1,H,Me and MeO) and a clear relationship between catalytic efficiency and the electronic nature of the ligand has been demonstrated for the reaction between oct-1-ene and CC1[sub]4.The relationship is more complex in the case of the analogous cyclohexene reactions which also displayed marked solvent effects, The reactions of both oct-1-ene, cyclohexene and CC1[sub]4 in the presence of [RuCl[sub]2(PPh[sub]3)[sub]3] have been studied in a wide range of solvents. The importance of solvent viscosity in determining yields in these radical reactions has been demonstrated. A preliminary study of the addition of CC1[sub]4 to cyclo-l,3-dienes was also made with specific emphasis on the investigation of the stereochemistry of the addition products. A study has also been made of the catalysedsynthesis of lactones by addition of trichloroacetic acid to alkenes in the presence of [RuC1[sub]2(PPh[sub]3)[sub]3]. The reaction has been extended to the synthesis of dibrominated lactones from tribromoacetic acid and alkenes. A method was developed for purification of the bromolactones, as they were found to be suseeptable to thermal decomposition.

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