Master of Science (MS)
Semester of Degree Completion
T. Howard Black
An area of recent research in the Black research group is an exploration of the potential of cation-initiated β-lactone ring expansions, accompanied by the elimination of a proton or other electrofuge, as a protocol for the synthesis of multisubstituted butenolides.
Γ-Bromo β-lactones were prepared via bromolactonization of the appropriate β,Γ-unsaturated acids under basic conditions. The nucleofugal bromine atom on the Γ-carbon was then employed to effect carbocation formation adjacent to the lactone ring oxygen atom; the most efficacious reagent combination was found to be silver nitrate in refluxing acetic acid. Generation of this cation initiated a migration of the β-lactone ring oxygen atom to the Γ-position, whereupon loss of the α-proton produced butenolides in 30 to 75% yield.
Successful implementation of this conceptually novel strategy will provide a versatile and expedient route for the synthesis of butenolides bearing a wide range of substitution patterns.
Cycloaddition of α-trimethylsilylketene (TMS ketene) to aldehydes bearing carbocation progenitors in the α-position provided α-trimethylsilyl β-lactones which were then examined as substrates for the ring expansion/elimination sequence. In contrast to aldehydes, ketones were transformed into α,β-unsaturated acids under the same conditions.
Huang, Jianhua, "Butenolide Synthesis via Cation-Initiated Ring Expansion/Elimination of β-Lactones" (1992). Masters Theses. 1970.