1. Asymmetric aldol and alkylation reactions using pyrrolidine-based chiral auxiliaries 2. Syntheses of pine sawfly pheromone precursors and structurally related compounds

Detta är en avhandling från Stockholm : Kemi

Sammanfattning: This thesis describes the syntheses of the 1-propionylatedauxiliaries (S)-(? )-2-(pyrrolidin-2-yl)propan-2-ol and (S)-(? )-2-(1-methoxy-1-methylethyl)pyrrolidine andtheir use in asymmetric aldol and alkylation reactions. Thesynthesis of 1-propionylated (2S,4R) 2-{4-[(tert-butyldimethylsilyl)oxy]pyrrolidin-2-yl}propan-2-olis also described. The effects on the stereoselectivity, byvariations of solvent, temperature, Lewis acids as additive aswell as the amount of additive are studied. None of thepropionylated auxiliaries exhibited remarkable selectivity foreither diastereomer in aldol reactions with benzaldehyde. Bestresults were obtained with SnCl2as additive giving asyn:antiratio up to 73:27, and Cp2ZrCl2and Cp2TiCl2giving a reversedsyn:antiratio up to 27:73 for the former auxiliary. Highselectivity for onesynand oneantidiastereomer were obtained with TMS-Cl as anadditive. The latter propionylated auxiliary was less selectivethan the former. Reversal insyn/antiselectivity was observed when Cp2ZrCl2and Cp2TiCl2was used with asyn:antiratio = 68:32 and 33:67. In alkylation reactions,the former propionylated auxiliary showed lower and similarselectivity with benzyl bromide andn-butyl iodide, compared with the literature. Enhancedselectivity was obtained in the benzylation reactions (78% and84% diastereomeric excess), with LiCl and Cp2ZrCl2as additives. Cp2ZrCl2and Cp2TiCl2resulted in lower selectivity in butylationreactions. High selectivity was obtained for the latterpropionylated auxiliary and with a reversal in selectivity,compared with the former. Benzylation reactions resulted in82-98% diastereomeric excess, with the highest selectivity ofCp2ZrCl2as additive. In butylation reactions the use ofLiCl resulted in highest diastereomeric excess (94%).The second part of the thesis describes the syntheses ofcompounds related to sex pheromones of pine sawflies. (2S,6R)-(? )-2,6-Dimethyl-1-octanol, a building blockin the synthesis of the sex pheromone of the pine sawflyMicrodiprion pallipesin high stereoisomeric purity wasprepared from the optically pure (S)-citronellal. Lipase-catalysed (Amano PS and Im-CRL)kinetic separations, based on selective acylation andesterification of (2R/S,6R)-2,6-dimethyl-1-octanol and the corresponding acidwere the key steps in this sequence. The alcohol precursors tosex pheromones ofDiprion nipponica,Macrodiprion nemoralisandMicrodiprion pallipeswere synthesised as racemicmixtures in moderate yields. Stereoisomeric mixtures of severalmethyl-branched long-chain 2-alkanols, structurally related tosex pheromone alcohol precursors of pine sawfly species, werealso synthesised in moderate yields. The key reaction in thesyntheses was the ring opening of&#947-butyrolactonesusing different alkyl lithiums as nucleophiles.Keywords: Chiral auxiliary, Stereoselectivity, Lewisacid, Aldol, Alkylation, Sex pheromone, Pine sawfly, Lipase,Synthesis, Diprion nipponica, Macrodiprion nemoralis,Microdiprion pallipes

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