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8.2.4.1.6 Method 6: Ramberg–Bäcklund Reaction

DOI: 10.1055/sos-SD-008-00826

Jonczyk, A.; Kowalkowska, A.Science of Synthesis, (200681052.

The reaction of α-halo sulfones possessing α-hydrogen(s) with a base, often sodium hydroxide, to give alkenes (via thiirane dioxides which extrude sulfur dioxide) is named the RambergBäcklund reaction.[‌579‌‌583‌] When this process is applied to chloromethyl cyclohexyl sulfone, it affords methylenecyclohexane in 80% yield.[‌584‌] When the starting sulfones contain more halogens, the reaction often gives mixtures containing haloalkenes, alkynes, and α,β-unsaturated sulfonic acids.[‌585‌‌588‌] The RambergBäcklund reaction may be carried out under phase-transfer catalysis conditions, in the presence of dilute sodium hydroxide, affording alkenes 83 in 7594% yield (Scheme 62).[‌183‌,‌589‌] Sulfones substituted with the trifluoromethyl group potentially appear to be very useful substrates, and they require equimolar amounts of tetrabutylammonium hydrogen sulfate for successful RambergBäcklund reaction.[‌589‌] Among other synthetic applications, this approach is used in the preparation of the Artemisia ketone from a trifluoromethyl-substituted oxo sulfone.[‌589‌] A one-pot phase-transfer-catalyzed reaction of dibenzyl sulfone with carbon tetrachloride leads directly to (E)-stilbene in yields of 94100%.[‌177‌,‌183‌]

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