Sulfones, vinyl desulfurization

Unsaturated sulfones were desulfurized by Li-EtNH2 without isomerization (Scheme 12), 4i while other procedures were unsuccessful. Isomerization was observed with the same reagent during the desulfurization of allyl and vinyl sulfones. ... 

Reductive desulfurization of 9-(phenylsulfonyl)furo[2,3- ]quinoline and its 2-methyl derivative can be effected by treatment with LAH in THF solution at reflux, but proceeded poorly with aluminum amalgam, the reagent of choice for the reductive cleavage of vinyl sulfones <83JOC774>. Raney nickel was used to remove a thiomethyl substituent from the central ring of a furochromone direct precursor to visnagan <89JOC448l>. 

LAH-CuCh used in moderate to large excess desulfurizes sulfides and dithioketals in good to very good yields (55-87%), but with allyl sulfides, migration of the double bond occurs. Finally vinyl phenyl sulfones are reductively cleaved in good yields (65%) without reduction of C=-C bonds even by an excess of reagent. ... 

Li, Na and K in hydrocarbons, ethereal solvents, HMPA or DMA have been used to desulfurize sul-fides, but applications are limited to simple sulEdes, and particularly to aryl alkyl sulfides. Since these desulfurizations were performed without protic solvent, the organometallics formed may react further and particularly with the solvent. Thus low temperatures were recommended. Potassium graphite (CgK) in excess in ether was also proposed for the desulfurization of allyl or vinyl sulfones, but this reagent is not free of disadvantages. ... 

However, this procedure also has a number of drawbacks. A large quantity of Hg must be used. Moreover, alkenic bonds are reduced during the desulfurization of conjugated dienyl vinyl sulfones, and p-eliminations take place in the presence of good vicinal leaving groups. ... 

Vinylic sulfoxide (30) is desulfurized to (31) with f-butyllithium (equation 80), and sulfone (32) affords triphenylethylene on reduction with aluminum amalgam or lithium aluminum hydride (equation 81). ... 

Quite analogously, reaction of 428 with methyl vinyl sulfone gave the hexacyclic product 431 as a mixture of C-18 stereoisomers. Reduction of 431 with di(2-methoxyethoxy)sodium aluminum hydride in dioxane under reflux gave a hydroxythiomethylamine, which was desulfurized with Raney nickel to afford a racemic hydroxyaspidofractinine. 

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