Stereoselective syntheses of functionalized tetrahydrofurans via intramolecular oxymetallations of allenes and syntheses of methyl nonactate homologues
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My research objective was to investigate two-step intramolecular nucleometallationcoupling reactions of allenes to form polyfiinctional heterocyclic molecules. This reaction sequence takes place by either: a) an intramolecular oxy- or aminomercuration of an allene followed by a transmetallation of the mercury by palladium(II), then a coupling reaction (e.g., with carbon monoxide and an alcohol to form estCTs); or b) an intramolecular oxy- or aminopalladation of an allene followed, in situ, by the coupling. The results of this investigation have led to: 1) the development of a stereospecific approach to cis-2-15-alkyltetrahydrofiiran-2-yl)-2-propenoates; 2) the discovery of a stereospecific reduction of cis-2-(5-alkyltetrahydrofuran-2-yl)-2-propenoates; and 3) the development of a general synthetic approach to natural and unnatural nonactic acid esters. Scheme 1 represents our basic idea for the intramolecular nucleometallation of allenes (1) using mercury or palladium salts. A metal-complexed allene (2) should cyclize to form an intermediate a-vinyl complex of the metal (3). The complex 3 (where M = palladium) can undergo carbonylation and alkoxide coupling in the presence of carbon monoxide and an alcohol to form substituted acrylate esters (4) which should be valuable intermediates for organic synthesis.