This thesis describes the application of (arene)Cr(CO)3 methodology to the Stereoselective and enantioselective synthesis of substituted arenes. Chapter one reviews the main methods of preparation and decomplexation of (arene)Cr(CO)<sub>3</sub> complexes and the electronic and steric influences of the Cr(CO)<sub>3</sub> unit on the arene. Chapter two demonstrates that the benzylic oxygen directing effect in complexation reactions operates via a direct oxygen bond to the incoming metal unit. Attachment of bulky ft-acceptor groups, such as t-butyldimethylsilyl, to the benzylic oxygen overrides this directing effect. Chapter three describes the regioselective Cl functionalisation of the cryptopine skeleton. Complexation of dihydrocrytopine gives only a single product, the relative configuration of the product being determined using an X-ray crystal structure analysis. Subsequent alkylation of the O-methyl derivative gives Cl alkylated products. Chapter four describes the regioselective ortho functionalisation of ephedrine and pseudoephedrine derivatives. Treatment of (1S,2R)-(N,O-dimethylpseudoephedrine) Cr(CO)<sub>3</sub> with n-butyllithium leads to exclusive removal of the pro-(R) ortho proton. The observed stereoselectivity arises via</em deprotonation from cyclic bidentate five-membered chelates. Chapter five describes the regioselective C4 and C5 functionalisation of (hydrocotarnine)Cr(CO)<sub>3</sub>. Complexation of 1-methylhydrocotarnine occurs to give exclusively the exo-1-methyl derivative. Further functionalisation to give the 1,5- and 4,5-dimethyl products is also described. Chapter six describes the synthesis of ortho substituted (benzaldehyde)Cr(CO)<sub>3</sub> complexes. Chiral material is available via preferential kinetic hydrolysis of, or classical separation of, the L-valinol derived imines. Chapter seven describes the Stereoselective addition of nucleophiles to (o-anisaldehyde) Cr(CO)<sub>3</sub> and (o-trialkylsilylbenzaldehyde)Cr(CO)3. With (o-anisaldehyde)- Cr(CO)<sub>3</sub> the additions are completely stereoselective giving the (RR,SS) diastereoisomer. With (o-trialkylsilylbenzaldehyde)Cr(CO)<sub>3</sub> the ratio of products is influenced by the nature of Lewis acidic species present. Chapter eight describes the Stereoselective benzylic elaboration of (o-methoxybenzyl methyl ether)Cr(CO)<sub>3</sub> achieved via selective removal of the exo benzylic proton from transition states with the methoxy groups anti to each other.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:315720 |
| Date | January 1989 |
| Creators | Goodfellow, Craig L. |
| Contributors | Davies, Stephen G. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:e2833156-aec2-42e5-b835-e9ddca4fa27c |
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