Demercuration azidomercuration

The formal addition of H—N3 across C—C double bonds can also be brought about via azidomercuration-demercuration, a process recently reviewed.267 In the presence of NaN3, Hg(OAc)2, Hg(02CCF3)2 or Hg(N03)2, in aqueous THF, methanol or DMF, alkenes undergo azidomercuration (equation 188).268-... 

Application of the azidomercuration-demercuration procedure to the 5-ene (9) gave the 6- and 5-azides (10) and (11) in the ratio 1 4 (Scheme 1). The synthesis of azido-sugars via 2,3-anhydro-furanosides has been reported. Methyl 2,3-anhydro-0 -D-lyxofuranoside (12) gave the 3-azide (13) in 95% yield, and its 5-0-tosyl ester (14) gave the 3,6-diazide (15) in 84% yield. In contrast, the 2,3-anhydro-riboside (16) gave a mixture of the 2- and 3-azides (17) and (18) in the ratio 3 2. However, substitution at C-5 of (16) resulted in steric hindrance of the approach to C-3 and consequently the 5-tosylate (19) afforded the 2,6-... 

Hydrazoic acid can be added to certain Michael-type substrates (Z is as defined on p. 975) to give 3-azido compounds. The reaction apparently fails if R is phenyl. Ammonia also adds to enol ethers CH2=CHOR to give CH3—CH(OR)N3, and to silyl enol ethers, but it does not add to ordinary alkenes unless a Lewis acid catalyst, such as TiCU, is used, in which case good yields of azide can be obtained. Ammonia can also be added indirectly to ordinary alkenes by azidomercuration, followed by demercuration, analogous to the similar procedures mentioned in... 

An improved method for the azidomercuration of alkenes with mercuric trifluoroacetate has been described.When applied to unsaturated carbohydrates it provides, after demercuration and reduction, a high-yielding synthesis of amino-sugars. 

The first successful approach was reported by Heathcock in 1969 using mercury(ll) salts. The reaction proceeds via an olefin azidomercuration followed by a reductive demercuration in the work-up. The azides derived from terminal olefins were obtained in 50-88% yield with good Markovnikov selectivity, while non-terminal olefins gave lower yields (Figure 4.2). An obvious drawback of this procedure is the use of a stoichiometric amount of mercury salts. This procedure also leads to the formation of potentially explosive Hg(N3)2. Nevertheless, this method is unique and reliable for the hydroazidation of monosubstituted non-activated olefins. 

---