Reductive desulfonylation, with sodium

Some Compounds Reductively Desulfonylated with Sodium Amalgam... 

Methylation with lithium dimethylcuprate and reductive desulfonylation with sodium in ethanol provides ( + )-exo-brevicomin (90) in 67% yield [158] (Scheme 105). 

Use of Sodium Amalgam. Reductive desulfonylation with metal amalgams, and particularly Na/Hg (5-6%), is the most widely employed and general method for all types of sulfones even though it requires the handling of substantial quantities of mercury, which is toxic and relatively expensive. 

From the experimental point of view, reductive desulfonylations with alkali metal arene radical anion complexes require a large excess of the radical anion, very short reaction times at low temperatures, and must be run under an inert atmosphere. Sodium or lithium naphthalenides in tetrahydrofuran at —78° or lower temperatures are typical reaction conditions. Tetrahydrofuran solutions of lithium naphthalenide are dark green. This color is lost when the substrate is added and restored once the reaction is finished. Upon completion, the excess reagent is quenched with a saturated aqueous solution of ammonium chloride or low molecular alcohols such as methanol or ethanol. 

Desulfonylation of a-sulfonylacetates. Desulfonylation of these substrates is not satisfactory by the usual methods (Zn-HOAc, Raney Ni-C,H5OH, sodium amalgam), but can be conducted in 70-75% yield with sodium-ethanol in THF (modified Bouveault-Blanc reduction). The substrates (2) are obtained by Wolff rearrangement of a-acyl-a-benzyl-sulfonyldiazomethanes (1).1... 

The reductive desulfonylation of vinylic sulfones has been mainly carried out with sodium and aluminum amalgams, Sml2, and Mg in M,Al-dimethyl-formamide (DMF) in the presence of chlorotrimethylsilane (TMSC1). The configuration of the double bond is not necessarily preserved in the desulfonylation of vinylic sulfones when Na/Hg is employed. This reagent is the most widely used when there is no need for stereochemical control as shown in Eqs. 2139 and 22.40... 

Use of Sodium Hydrogen Telluride. Certain a-functionalized-a,(3-unsaturated sulfones are desulfonylated using sodium hydrogen telluride in ethanol at room temperature.164-1663 u - Me thy I (hu Mi, j3-unsaturated sulfones are reduced to give vinylic thioethers in good yields albeit with moderate selectivities (Eq. 97).164 On the other hand, a-methylsulfonyl chalcones suffer tandem reduction-desulfonyla-tion in the presence of DMF as cosolvent.165,166a... 

Alternatively, reductive desulfonylation of the desilylated cycloadduct with 6% sodium amalgam in buffered methanol afforded a 2 1 mixture of isomers. The products are formally the result of TMM Pd addition to 2-cyclohexenone (poor yielding) followed by ketone reduction58. 

Sulfonamides are very difficult to hydrolyze. However, a photoactivated reductive method for desulfonylation has been developed.240 Sodium borohydride is used in conjunction with 1,2- or 1,4-dimethoxybenzene or 1,5-dimethoxynaphthalene. The photoexcited aromatic serves as an electron donor toward the sulfonyl group, which then fragments to give the deprotected amine. The NaBH4 reduces the radical cation and the sulfonyl radical. 

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