Master of Science (MS)
Semester of Degree Completion
T. Howard Black
Exposure of α-trimethylsilyl β-lactones to magnesium bromide or boron trifluoride etherate in diethyl ether solvent resulted in the smooth generation of β,γ-unsaturated acid derivatives in good yield and isomeric purity. It is believed that this reaction occurs via the formation of a stable tertiary carbocation at the γ-carbon resulting from cleavage of the carbon-oxygen sigma bond due to the complexation of the Lewis acid with the ring oxygen atom. Rapid loss of an adjacent electrofuge then furnishes the unsaturated acids. The β-lactone precursors were prepared by a [2+2] cycloaddition of an aldehyde and an alkyl trimethylsilyl ketene. This method was designed in the hope of producing germacranolide compounds such as aristolactone from an intramolecular [2+2] cycloaddition, but unfortunately produced cyclo β,γ-unsaturated acids which were previously difficult to obtain. A detailed synthetic methodology leading to the intramolecular Lewis acid catalyzed [2+2] cycloaddition reaction is of prime interest and is discussed in detail.
Yates, Bryan E., "Studies Directed Toward the Synthesis of Germacranolides via [2+2] Cycloaddition Followed by Ring Expansion/Elimination of β-Lactones" (1994). Masters Theses. 2029.