Hydration mercury-catalysed

In fact the workers who wanted 7 for photochemical addition to alkenes (chapter 32) chose1 to use propargyl bromide 14 and an enamine 13 of the aldehyde 12. Mercury-catalysed hydration of 15 gave 8 which cyclised to 7 in base. 

The mercury-catalysed hydration of alkynes is a useful reaction which leads, via protonolysis of the organomercury compound and the enol, to a methylene ketone (Scheme 3.29). 

Alkynes undergo electrophilic, radical and nucleophilic addition, including a mercury-catalysed hydration to form methylene... 

The additions of iodine azide (equations 99, 100) and the mercury catalysed hydration (equation 101) were rationalized on the basis of Ad reactions with cyclic intermediates having relatively little car-bonium ion character. Orientation is then dependent on the inductive effects of the methyl and bromo substituents with little orientational effect of the phenyl group. In contrast, the orientation of the acid... 

A further consequence of the stabilisation of carbanionic centres at pyridine a- and y-positions is the facility with which vinyl-pyridines, " and alkynyl-pyridines, add nucleophiles, in Michael-like processes (mercury-catalysed hydration of alkynyl-pyridines goes in the opposite sense " ). 

This reaction is widely utilised in organic synthesis, when carbonyl groups may be protected as the thioacetals or thioketals. Unlike acetals or ketals, the thio compounds do not undergo acid catalysed hydration, and may be used in acidic reaction conditions. The metal-directed hydrolysis is rationalised in terms of the soft-soft interaction of the sulfur with the metal cation, in contrast to the hard-soft interaction with a proton. Hydrolysis is readily achieved on treatment with aqueous mercury(n) or silver(i) salts. Once again, the... 

The anthracyciinone class of anticancer compounds (which includes daunomycin and adriamycin) can be made using a mercury (I I )-promoted alkyne hydration. You saw the synthesis of alkynes in this class on Chapter 9 where we discussed additions of metallated alkynes to ketones. Here is the final step in a synthesis of the anticancer compound deoxydaunomycinone the alkyne is hydrated using Hg2+ in dilute sulfuric acid the sulfuric acid also catalyses the hydrolysis of the phenolic acetate to give the final product. 

Acid-catalysed hydration of conjugated diyncs is slower than that of simple alkynes, but still occurs under relatively mild conditions in the presence of sulphuric acid or especially sulphuric acid and mercury(ii) sulphate. Thus 2,3-butanedione (200) is obtained readily from butadiyne, without isolation of the intermediate monohydration product, 3-butyn-2-one (199). 

Oxidation of organoboranes to alcohols is usually effected with alkaline hydrogen peroxide. The reaction is of wide applicability and many functional groups are unaffected by the reaction conditions, so that a variety of substituted alkenes can be converted into alcohols by this procedure. Several examples have been given above. A valuable feature of the reaction is that it results in the overall addition of water to the double (or triple) bond, with a regioselectivity opposite to that from acid-catalysed hydration. This follows from the fact that, in the hydroboration step, the boron atom adds to the less-substituted carbon atom of the multiple bond. Terminal alkynes, for example, give aldehydes in contrast to the methyl ketones obtained by mercury-assisted hydration. 

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