UBC Theses and Dissertations
Synthetic studies using B-keto esters Sum, Phaik-Eng
The dianions of β-keto esters have been generated using one equivalent of sodium hydride and one equivalent of n-butyl1ithium or two equivalents of lithium diisopropyl-amide. The reaction of these dianions with various epoxides was studied. On treatment of lithio sodio methyl aceto-acetate (55) with one and one-half equivalents of ethylene oxide and on subsequent treatment with acid, a tetrahydro-furylidene acetate 95, formed from the cyclization of the intermediate alcohol. Methyl α-(tetrahydro-5-methy1-2-fury1i-dene) acetate (96) was also synthesized by treating the di-anion with propylene oxide. The alkylation of these dianions from β -keto esters with α-chloroethy1 ethyl ether or α-ch1oromethy1 methyl ether was also investigated. This provides a convenient preparation of the precursors to Nazarov's reagent which are very useful in the Robinson type annelation. The preparation of methyl 5 - methoxy-3-oxopentanoate (12 0) could be easily achieved in a single step synthesis by treating the lithio sodio methyl acetoacetate (55) with one equivalent of chloromethyl methyl ether. Similarly, methyl 5-ethoxy-3-oxohexanoate (12 9) and methyl 5-methoxy-3-oxohexanoate (130) were prepared using our dianion reaction. The synthesis of large ring compounds using the internal double alkylation of these dianions with dihalo-alkanes in a one-step reaction was found to be rather difficult. The isolated products were a mixture of the bis β -diketo esters and a y-alkylated mono-halo compound in approximately equal amounts. However, on treatment of the mono-halo compound with one equivalent of sodium methoxide in refluxing methanol, the intramolecular cyclization at the a-carbon was easily achieved. The mono-halo β-keto esters could also be cyclized via their dianions to the cyclic or spiro β-keto esters.
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