Sulfoxide, Ammonium, and Oxonium Ylide Rearrangements

The tactical use of this rearrangement is important in the context of the broader strategic plan. The combination of the electron-deficient diene (201) and the electron-rich dienophile (202) sets up a cycloaddition reaction that proceeds at a convenient rate and with desired regiocontrol. The recognition that, after the rearrangement, the sulfoxide is the synthetic equivalent of an allylic alcohol exemplifies brilliant strategic planning and synthetic execution. 

The use of ammonium ylides in asymmetric [2,3]-rearrangements has been highlighted in several elegant settings [22, 23]. As an illustrative example, Baldwin demonstrated that the enolate derived from 213 could be rearranged into 214 as a single diastereomer (Equation 24) [113]. This transformation proved pivotal for the preparation of penicillin derivatives. 

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