Sodium amalgam demercuration

Tri-n-butyltin hydride can also be used for reductive demercuration.20 An alternative reagent for demercuration is sodium amalgam in a protic solvent. Here the evidence is that free radicals are not involved and the mercury is replaced with retention of configuration.21... 

While the demercuration of (3-acyloxymercurials has not received much attention, sodium borohydride or alkaline sodium borohydride have been most widely employed for this task. Hydrolysis to the corresponding alcohol or reversion to alkene are significant side reactions, however, and they are sensitive to the solvent used.4991500 Sodium amalgam and tri-n-butyltin hydride501 have also been utilized as reducing agents. 

Some years ago it was reported that cyclohexene reacted with mercury(II) nitrate and acetonitrile in nitric acid to give the metallic derivative (89), which, in turn, underwent demercuration with sodium amalgam, producing the corresponding amide (Scheme 48). Later investigators " found that less severe... 

Treatment of azido(2-azidocyclopropyl)mercury(II) derivatives with sodium borohydride under basic aqueous conditions led to concomitant C —Hg cleavage and C —H bond formation and formation of the corresponding azidocyclopropanes. Reductive demercuration also took place when (cw-2-azidocyclopropyl)bromomercury(II) derivatives were reacted with sodium amalgam and deuterium oxide mercury was replaced stereospecifically with deuterium leading to c -l-azido-2-deuteriocyclopropanes. The yields are generally very low (< 25%). 

Most useful of the demercuration procedures reported is the use of alkaline sodium borohydride244 or sodium-mercury amalgam.243 246 Reduction with UAIH4 affords the corresponding amines.24 ... 

Alkaline sodium borohydride is the preferred demercuration reagent, but sodium-mercury amalgam in D2O is best for stereospecific reduction with retention.268... 

The demercuration of (3-alkoxymercurials is usually best effected using alkaline sodium borohydride. Few rearrangements during this free radical reduction process have been observed 429 When the mercury moiety is positioned a to a carbonyl group, alkaline H2S430,431 or 1,3-propanedithiol316 provide alternatives that afford complementary stereochemical results (equation 262). The use of sodium-mercury amalgam is also useful for stereospecific reduction.432 433... 

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