Synthesis of Highly Functionalized 2-Pyranone from Silyl Ketene.
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We report a highly functionalized 2-pyranone small molecule prepared from tert-butyl diphenyl silyl ketene using an alkoxide catalyst and thermally induced rearrangement. Treatment of the silyl ketene with a substoichiometric amount of alkoxide led to the formation of a trimer which was isolated and fully characterized; heating this trimer in a 1,4-dioxane solution induced a thermal rearrangement, yielding the product 2-pyranone. The isolated intermediate and product are characterized by 1D and 2D nuclear magnetic resonance (NMR) spectroscopies, mass spectrometry, and single crystal X-ray diffraction. A mechanism for the thermally induced rearrangement is proposed based on 1H NMR studies, and a rate law is derived from the proposed mechanism with steady-state approximation. This work illustrates a route for the formation of highly functionalized and modifiable 2-pyranone motifs with potential biological activity. The formation of the trimer, and thus the functionalized 2-pyranone, is highly dependent on the silyl substituents and alkoxide counterion and thus indicates the intriguing reactivity of highly functionalized small molecules.