D.Sc. / Please refer to full text to view abstract

The preparation and synthetic utility of various β-trialkylstannyl-α,β-unsaturated carbonyl compounds is described. In this connection, treatment of tetrahydrofuran solutions of Me₃SnLi and n-Bu₃SnLi with one equivalent of PhSCu led to the in situ formation of PhS(Me-₃Sn)CuLi 72 and PhS (n-Bu₃Sn)CuLi 73, respectively. The latter reagents readily transferred, in a conjugate sense, the trialkyl-stannyl group to α,β-unsaturated carbonyl systems. In particular, these trialkylstannylcuprate reagents efficiently transformed β-iodo enones 4 into β-trialkylstannyl-α, β-unsaturated ketones 11, a new class of organotin derivatives. Likewise, treatment of the β-iodo enones 4_with Me₃SnCu • LiBr • SMe₂ 94, prepared by the reaction of Me₃SnLi with one equivalent of Me₂S*CuBr, gave the corresponding 6-trimethylstannyl enones in good yield. Two of these β-trialkylstannyl enones, β-trimetehyl-stannyl-2-cyclohexen-l-one 70 and β-tri-n-butylstannyl-2-cyclohexen-l-one, 74 were transformed into the vinylithium reagent 111. Sequential treatment of the enones 70 and 74 with lithium diisopropylamide and tert-butyldimethylsilyl chloride in the presence of hexamethylphosphoramide gave the enol silyl ethers 110 and 108, respectively. Transmetalation of the compounds 110 and 108 was accomplished by treatment of these substances with 1.1 equivalent of an alkyllithium reagent. Reaction of the resultant vinyllithium reagent 111 with electrophilic reagents proceeded smoothly to afford the corresponding substituted 1,3-cyclohexadienes in good yield. The reaction of PhS(Me₃Sn)CuLi 72 with various a, 6-acetylenic esters is also described. The course of the reaction could be controlled experimentally so as to produce, highly stereoselectively, either the (E) - or the (Z)-β-trimethylstannyl-α, β-unsaturated esters. Treatment (THF, -78°C) of PhS (Me₃Sn)CuLi 72 with a, β-acetylenic esters in the presence of a proton source (e.g., MeOH) gave the corresponding (E)-S-trimethylstannyl-a,g-unsaturated esters in good yield. Reaction of 7_2 with α,β-acetylenic esters at slightly higher temperatures (-48°C) in the absence of a proton source resulted in the formation of the corresponding (Z)-isomers. Reaction of ethyl (Z)-3 -tosyloxyacrylate 180 with Me₃SnCu*LiBr-SMe₂ 94 and n-Bu₃SnCu•LiBr*SMe₂ 181 gave the corresponding (Z)-β-trialkylstannylacrylates. Finally, two of the β-trimethylstannyl esters, ethyl (E)-3-trimethy1stanny1-2-butenoate 163 and ethyl (Z)-3-trimethylstannyl-2-butenoate 166, were converted into the geometrically isomeric trimethylstannyl dienes 184 and 185, respectively. Both of these substances underwent rapid and complete transmetalation when treated with 1.2 equivalents of methyllithium in tetrahydrofuran. The resultant 4-lithio-l,3-pentadienes (186 , 187) reacted smoothly with a variety of electrophiles to produce the corresponding substituted dienes (192 and 193). / Science, Faculty of / Chemistry, Department of / Graduate

M.Sc. / This study initially focused on the synthesis of a set of triaryl phosphine ligands, encompassing a broad range of electron withdrawing functionalities on the ortho-position of one of the aryl rings. These varying moieties were readily incorporated into diphenylphosphino benzaldehyde as starting material through both Wittig and Knoevenagel chemistry. The ligands produced were tested in the Pd-catalysed Suzuki reaction. The electronic as well as the steric nature of the alkene ligands largely dictated the activities observed: the more electron poor or the bulkier the ligand, the higher the activity observed in the Suzuki reaction. This is in contrast to much work in the literature stating that highly active Suzuki catalysts require a very electron rich system. At the same time, the literature indicates that co-ordinatively unsaturated Pd-complexes are also active catalysts. The activities observed were ascribed to the ability of these electron poor bulky phosphine alkene ligands to stabilise or promote the reductive elimination step of the Suzuki mechanism in preference to the oxidative addition step, which is the typical rate determining step. The study then investigated carbonylation reactions, specifically the methoxycarbonylation and hydrocarboxylation reactions, which are typically Brønsted acid co-catalysed. The alternative was the first time use of metal-triflate based Lewis acids as co-catalysts in these types of reactions. Thus, a systematic study was performed. It was found that metal trifluoromethane sulfonate (hereafter referred to as triflate) based Lewis acid co-catalysts outperformed the typical Brønsted acid co-catalysts by between one and a half to two and a half times on the rate of the methoxycarbonylation reaction, depending on the substrate used. The system was tested with Pd loadings in the region 2–0.03 mol%. A competing heat-induced styrene polymerisation reaction ultimately affected the results at such low Pd loadings. A low level kinetic analysis was performed indicating zero order kinetics on the alkene concentration of the reaction, with a fractional order dependence on the Lewis acid concentration. There was little to no effect on the linear/branched ratio of the product in response to the use of the Lewis acid. The nature of the metal within the metal triflate based co-catalyst also seemed to be critical to the reaction, with the 4+ based Zr and Hf ultimately providing the highest obtainable turn over frequencies, the 1+ and 2+ based metals providing no conversion, and reactivity in the presence of the 3+ metals depended on the specifics of the reaction. In addition to a great deal of work being performed on styrene and ethylene as substrates, reactions using phenylacetylene were also optimised. Here, it was found that the bidentate BINAP ligand and the literature preferred ligand, PyPPh2 afforded good catalyst activity. Both of these ligands offered much faster catalyst systems than PPh3 and various other bidentate ligands tested.

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Call number: LD2668 .T4 1949 M61 / Master of Science

Call number: LD2668 .T4 1959 M56

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy