Mercury hydride alkenes

Addition of tin and mercury hydrides to unsaturated ketones 5-22 Free-radical addition of aldehydes or ketones to olefins 5-24 Hydroacylation of alkenes... 

Cyclopentyl radicals substituted in the /1-position relative to the radical center are formed during the solvomercuration/reductive alkylation reaction of cyclopentene34. The organomer-curial produced in the first solvomercuration step is reduced by sodium borohydride and yields free cyclopentyl radicals in a radical chain mechanism. Addition of alkenes can then occur tram or cis to the / -alkoxy substituent introduced during the solvomercuration step. The adduct radical is finally trapped by hydrogen transfer from mercury hydrides to yield the tram- and ris-addition products, The transicis ratio depends markedly on the alkene employed and it appears that the addition of less reactive alkenes occurs with higher trans selectivity. In reactions of highly substituted alkenes, this reactivity control is compensated for by steric effects. Therefore, only the fnms-addition product is observed in reactions of tetraethyl ethenetetracarboxylate. The choice of alcohol employed in the solvomercuration step has, however, only a small influence on the stereoselectivity. 

Perlmutter used an oxymercuration/demercuration of a y-hydroxy alkene as the key transformation in an enantioselective synthesis of the C(8 ) epimeric smaller fragment of lb (and many more pamamycin homologs cf. Fig. 1) [36]. Preparation of substrate 164 for the crucial cyclization event commenced with silylation and reduction of hydroxy ester 158 (85-89% ee) [37] to give aldehyde 159, which was converted to alkenal 162 by (Z)-selective olefination with ylide 160 (dr=89 l 1) and another diisobutylaluminum hydride reduction (Scheme 22). An Oppolzer aldol reaction with boron enolate 163 then provided 164 as the major product. Upon successive treatment of 164 with mercury(II) acetate and sodium chloride, organomercurial compound 165 and a second minor diastereomer (dr=6 l) were formed, which could be easily separated. Reductive demercuration, hydrolytic cleavage of the chiral auxiliary, methyl ester formation, and desilylation eventually led to 166, the C(8 ) epimer of the... 

A useful aspect of the mercury(II) hydride method is that it can be directly coupled with the many standard techniques for heteromercuration of alkenes and cyclopropanes. The resulting overall transformation adds a heteroatom and a carbon atom across the carbon-carbon double bond of an alkene or the carbon-carbon single bond of a cyclopropane. This is a difficult transformation to conduct by standard ionic techniques. An alkene thus becomes an equivalent of synthon (12) and a cyclopropane of synthon (13 Scheme 34). Many equivalent transformations (like haloetherification and phenylselenolactoniza-tion) are available to make precursors for tin hydride mediated additions. 

While allylic oxidation products may arise by elimination of a metal hydride from an intermediate adduct or metal-alkene complex, allylmercury species (34) are thought to be intermediates in the case of mercury(II) acetate. A number of pathways have beien suggested, for example involving radical and carbenium ion intermediates, and addition-elimination and rearrangement inocesses. ... 

In the laboratory, alkenes are often hydrated by the oxymercuration procedure. When an alkene is treated with mercury(II) acetate rHg(02CCH3)2, usually abbreviated Hg(OAc)2] in aqueous tetrahydrofuran (THF) solvent, electrophilic addition to the double bond rapidly occurs. The intermediate organomercury compound is then treated with sodium boro-hydride, NaBH4, and an alcohol is produced. For example ... 

Rearrangement of the initial insertion product occurs in the reaction of various vinylic palladium halides with alkenes . The vinylic palladium halides are prepared in situ from vinyl mercurials and palladium halides. The initial insertion products undergo a jS-metal hydride elimination followed by a reverse readdition to form relatively stable n-allylic Pd complexes ... 

Mercury compounds 66,305,313 Metal alkene compounds 76, 304 Metal alkyl compounds 66, 296, 302 Metal alkyne compounds 84, 307 Metal ammine complexes 296. 309 Metal aryl compounds 158 Metal azides 92, 295. 321 Metal carbonyl compounds 121, 294, 295, 309, 314, 317 Metal cyano compounds 297, 303 Metal ethylene complexes 73, 296, 304 Metal halides 297, 303 Metal hexafluoro compounds 304 Metal hydrides 293, 323 Metal-ligand vibrations 292 Metal olefin compounds 73, 76, 296, 304... 

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