Degree Name
Master of Science (MS)
Semester of Degree Completion
1994
Thesis Director
T. Howard Black
Abstract
Our research group has been interested in β-lactones as useful synthetic intermediates. Transformations of β-lactones, generally ring expansion/opening processes initiated by Lewis acids via ionization/cation-rearrangement or elimination mechanisms, provide efficient protocols for the syntheses of biologically important butyrolactones, β,γ-unsaturated carboxylic acids, or butenolides.
α-Trimethylsilyl β-lactones, synthesized via the BF3- catalyzed [2+2] cycloaddition of trimethylsilylketene to carbonyl compounds, spontaneously undergo ionization and trimethylsilyl group migration to form α,β-unsaturated trimethylsilyl esters. The trimethylsilyl moiety facilitates the ionization process because of its β-cation stabilizing ability. The two-carbon homologated α,β-unsaturated acids are formed in yields from moderate to high (41-99%) upon aqueous workup. This one-pot procedure, which occurs under mildly acidic conditions, provides an effective, nonbasic alternative to the Wittig reaction.
The only current drawback to this method is that α,β-unsaturated acids are formed as an approximately 1:1 mixture of E/Z isomers, which reflects the cis-trans ratio of the β-lactone intermediates. The low stereoselectivity, probably a consequence of the stereorandom nature of the trimethylsilylketene cycloaddition reaction, could possibly be improved by employing more sterically demanding alkyl silyl ketenes or Lewis acids.
Recommended Citation
Zhang, Yong, "Carbonyl Homologation via α-Trimethylsilyl β-Lactone Rearrangement: A Nonbasic Wittig Alternative" (1994). Masters Theses. 2052.
https://thekeep.eiu.edu/theses/2052
