Reaction deoxymercuration

The other point concerns the persistent controversy about the detailed mechanisms of general reactions of this type—i.e., the deoxymercuration reactions, not only of methoxycarbonyl compounds but also of the corresponding olefin adducts. These are clearly concerted processes that are aided in some way by coordination of X- on the mercury and coordination of H+ on the oxygen. There has been controversy, in which Wright and others have participated, as to whether the detailed mechanism involves a cyclic intermediate, in other words whether undissociated HX participates in the reaction or whether the assistance at the metal and oxygen centers are independent processes. Have you any comments on this ... 

Dr. Dessy First, I think Maurice Kreevoy feels that the deoxymercuration reaction... 

Price and Hammett s rule has found confirmation in the reaction of benzaldehyde with acetone and ethyl methyl ketone (Gettler and Hammett, 1943), in the acid-catalyzed hydration of olefins (Taft, 1956a), in the hydrolysis of esters catalyzed by ion-exchange resins (Samelson and Hammett, 1956), in acid-catalyzed deoxymercuration (Kreevoy et al., 1962), and in the esterification of carboxylic acids in methanol (Smith, 1939). Taft (1956b) has noted that the rule seems to require the following modifications. The entropy-bearing substituent... 

In the reaction between peroxymercurials and sodium borohydride, epoxide formation and deoxymercuration compete with hydrogenodemercuration (Scheme 30). Except for the synthesis of t-butyl... 

Apparently this procedure gives higher yields of carbonyl products than obtained with Pd(II) and the olefin alone. This procedure overcomes the low solubility of the olefins in aqueous solution. There is the possibility that the reaction proceeds via deoxymercuration, followed by direct reaction of Pd(II) with the olefin. However this seems unlikely, and the transmetallation reaction for oxymercurials have been demonstrated previously and the yields using mercurials are much higher than in the case of direct reaction with olefins. 

Evidence that deoxymercuration does not occur to give free olefin, followed by oxidation by Pd(II) to give product, is provided by the fact that undec-l-ene was not oxidized by PdCl2 under the reaction conditions in 2 hours, but a 63% yield was obtained in 30 minutes when the mercurial was employed. A very significant deuterium-labeling experiment was also carried out. 2-d -3,3-Dimethylbut-l-ene was prepared. 

Similarly to the mechanism of the Claisen rearrangement, the Overman rearrangement is a suprafacial, concerted, nonsynchronous / 3,37-sigmatropic rearrangement. The reaction is irreversible, which is the result of the significant driving force associated with the formation of the amide functionality. The mechanism of the metal catalyzed reaction is believed to proceed via an iminomercuration-deoxymercuration sequence and it is only formally a [3,3]-sigmatropic shift. 

Solvolytic deoxymercuration catalysed by iodide has been reported and the reaction shows both a first- and second-order component in iodide - It seems unlikely that other halides will be as useful as iodide in dehalogenation as they are oxidised less easily. Rearrangement rather than gamma elimination is observed when 1,3-dihalosubstrates are treated with iodide ion . ... 

The problem of the oxymercuration reaction, and the deoxymercuration process, alluded to above, has only begun to resolve itself in the last few years. The problem has been fundamentally one of assigning stereochemistry and mechanistic pattern to the processes... 

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