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36.5.1.27 Method 27: Rearrangement of Sulfoxides

DOI: 10.1055/sos-SD-036-00485

Hodgson, D. M.; Humphreys, P. G.Science of Synthesis, (200836648.

The suprafacial [2,3]-sigmatropic rearrangement of allylic sulfoxides 159 in the presence of a thiophile such as trimethyl phosphite (MislowEvans rearrangement) generates E-allylic alcohols 160 typically in 7080% yields.[‌348‌,‌349‌] The rearrangement is reversible, so the presence of a thiophile is essential to bias the equilibrium toward the desired allylic alcohol products.[‌350‌,‌351‌] Allylic sulfoxides can also be used to introduce further functionality by a deprotonationalkylation sequence, prior to the addition of trimethyl phosphite that induces the rearrangement of the intermediate substituted sulfoxides 161 to afford the allylic alcohols 162 (Scheme 75).[‌352‌] The deprotonation/alkylation step is generally selective for alkylation at the α-position of the parent allylic sulfoxide, although the addition of ketones, aldehydes, or esters to the carbanions results in a substantial amount of electrophile trapping at the γ-position, even at 100°C.[‌348‌] Problems of competitive γ-alkylation with alkyl halide electrophiles can be overcome by the addition of a heterocycle at the sulfur atom such as 2-pyridyl or 2-imidazoyl, which allow predominantly α-alkylation due to the chelating effect of the heteroatom.[‌348‌] If a quaternary stereocenter is generated by deprotonation/alkylation then E/Z-alkene mixtures are typically generated, unless one substituent is substantially more sterically demanding than the other.

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