Mercury groups

The Giese reaction has been used for reductive cyclization of a,/l-enones containing an isolated terminal double bond. Solvomercuration can be carried out selectively on the latter group. On hydride reduction, the mercurial group is reduced preferentially and undergoes addition to the enone group. Experimentally, no products resulting from prior reduction of the enone are observed. Yields of cyclized products are usually satisfactory.4... 

Group 2 (also zinc, cadmium and mercury, Group 12d)... 

The products undergo the usual replacements of the mercury group, such as reduction with alkaline sodium borohydride and iodination. Carbonylation is particularly useful an example is a new synthesis of coumestan (1, equation 1). 

Pyrazoles were chloromercurated at C-4 giving (316) by reaction with mercury(II) chloride (B-76MI40402, 66AHC(6)347). The mercury group in (316) behaves in a variety of reactions just as phenylmercury chloride. 1-Phenylpyrazole reacts with mercury(II) acetate to yield the 4-acetoxymercury derivative (317). The same reactions with 3 (5)-phenylpyrazole also introduce the acetoxymercury group at position 4 and not on the nitrogen atom. 

When equimoiecular quantities of mercuric acetate and o-toluidine react in aqueous solution, the resulting diacetate melts at 208° C. The position of the acetoxy mercuri groups has not been determined, but they are apparently not 8 5 or 4 6. 

The /-transition metals are located between Groups HA and IflA in the periodic table. Strictly speaking, a /-transition metal must have a partially filled set of d orbitals. Zinc, cadmium, and mercury (Group IIB) and their cations have completely filled sets of d orbitals, but they are often discussed with /-transition metals because their properties are similar. All of the other elements in this region have partially filled sets of d orbitals, except the IB elements and palladium, which have completely filled sets. Some of the cations of these latter elements have partially filled sets of d orbitals. 

There are some examples of nucleophilic displacement of a suitably activated bromine by fluoride, but there have been instances where such reactions are unsuccessful <93AHC(57)291>. Electrophilic methods do not include direct fluorination, but metallic derivatives provide carbanions which react with fluorine sources. Thus, 2- and 4-fluoroimidazoles have been made from the lithioimidazoles, for example, perchloryl fluoride converts 2-lithio-l-methylimidazole into the 2-fluoro derivative in more than 50% yield. Access to 4- and 5-fluoroimidazoles is even more convenient from the trimethylstannyl derivatives using fluorine or caesium fluoroxysulfate as the electrophile . Mercury groups react in much the same way, but they are more difficult to prepare and purify <86BSF930>. 

---