Lewis Acid Catalyzed Cycloadditions

Abstract

<p> This thesis describes an attempt to develop a potentially useful route to seven-membered carbocycles. α-Diketones and their enol ether derivatives were proposed to be suitable three-carbon cycloaddition dienophiles when complexed with a Lewis acid. Reaction with 1,3-dienes should then lead to the desired cycloheptyl system.</p> <p> 1H-NMR and 13C-NMR studies were used to determine the stoichiometry and charge delocalization of complexes formed between 2,3-butanedione, 1,2-cyclohexanedione, 2-methoxy-cyclohex-2-en-1-one and the Lewis acids TiCl4 and SnCl4. Observations from these studies suggested that 1,2-cyclohexanedione and 2-methoxy-cyclohex-2-en-1one could behave as substituted allyl cations when complexed with TiCl4 or SnCl4.</p> <p> Reaction of the 1,2-cyclohexanedione/TiCl4 and 2-methoxy-cyclohex-2-en-1one/ TiCl4 complexes with 1 ,3-butadiene gave rise to six-membered carbocycles from [4C+2C] cycloadditions. The reaction of 2,3-butanedione-mono-trimethylsilyl enol ether/TiCl4 complex with 1,3-butadiene gave a mixture of the [4C+2C] and [4C+3C] cycloaddition products.</p>