Desulphonylation oxidative

Eisch, Behrooz and Galle196 give compelling evidence for the intervention of radical species in the desulphonylation of certain acetylenic or aryl sulphones with metal alkyls having a lower oxidation potential at the anionic carbon. The primary evidence presented by these workers is that the reaction of 5-hexenylmagnesium chloride outlined in equation (85) gives a mixture of desulphonylation products, in accord with the known behaviour of the 5-hexenyl radical, in which the cyclopentylmethyl radical is also formed. 

Another approach to an oxidative desulphonylation reaction is to oxidize an a-sulphonyl carbanion with an oxidizing agent that is also nucleofugal. An example of this was presented by Little and Sun Ok Myong203 who used a molybdenum peroxide complex (M0O5.Pyridine.HMPA) as the oxidant. However, this reagent is expensive and... 

The carbanion generated from deprotonation of the w-carbon atom of sulpholene reacts with aldehydes and ketones to give alcohols. Sulphur dioxide extrusion from the products results in (E)-a-hydroxy-l,3-dienes (equation 72), or dehydration followed by thermal desulphonylation results in trienes117. Dienones can be obtained if the initial condensation is conducted with an aldehyde, followed by oxidation and sulphur dioxide removal117. 

Base-promoted desulphonylation of this compound provides methyl retinoate (19) (aIl- 13Z=5 l). The Cio-sulphone 28 also works as a coupling partner of 25 (Scheme 9) [11]. The Cio-disulphone 29 thus obtained is converted into 30 by successive oxidation, Pummerer reaction, NaBH4-reduction, Jones oxidation and methylation with diazomethane. Treatment of 30 with NaOMe in MeOH furnishes methyl retinoate (18) (all- 13Z=6 4). 

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