Dienes alkoxymercuration

Furthermore, more recent work about the monoalkoxymercuration of a series of conjugated dienes with different mercury salts has shown157 that the alkoxymercuration of these compounds proceeds in two steps, the first being the formation of 1,2-adducts in which, with the exception of the mercuration of a-terpinene, the alkoxy group occupies the allylic position. The 1,2-alkoxymercurials are in equilibria with the corresponding... 

The alkoxymercuration-demercuration of alkenes, dienes and alkynes in the presence of alcohols provides an even more versatile approach to the corresponding ethers than the acid-catalyzed process. This reaction has been extensively studied and thoroughly reviewed recently.415 The reaction of alkenes is best carried out using meicury(II) acetate or, for more highly substituted alcohols or alkenes, mercury(II) trifluoroacetate (equation 257).416,417... 

The alkoxymercuration of dienes and polyenes has been extensively studied. Mono-, di- or poly-mer-curated adducts are formed as expected based on results from the alkoxymercuration of analogous alkenes, but the product distribution varies depending on the nature of the diene or polyene. 

The alkoxymercuration of conjugated dienes is more complex since these compounds are less reactive than simple alkenes and the products often react further to afford dimercurated products whose regio- or stereo-chemistry is strongly affected by the initial product. For example, 1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene react with meicuiy(II) acetate in methanol to produce 1,2-adducts (equation 265).443-446 These adducts sometimes rearrange with time.446 1,3-Butadiene reacts further to afford primarily the meso adduct of double 1,2-additions.447 Surprisingly, little additional work has been reported on reactions of conjugated dienes. 

Electrophilic Addition to Alkenes, Hydroxy- and alkoxymercurations of alkenes have been performed in micellar SDS. Hydroxymercuration of (1) with mercury(II) acetate, followed by reduction with sodium borohydride, gave a greatly enhanced yield of (2) in micellar SDS (90%) relative to that obtained in THF-H2O (20-25%) (eq 2). Also, the reactions of (1) and the related limonene gave greater cyclic ether diol product ratios in the SDS environment than in aq THF. Both the enhanced 3delds and ratios were attributed to anisotropic solubilization of the alkylmercurial intermediate in a relatively H2O poor mIceUar microenvironment. The hydroxymercuration of an aromatic diene, /Mliallylbenzene, did not display enhanced chemoselectivlty (mono vs. diol formation) in micellar SDS relative to that obtained in THF-H2O. This result suggests that the mIceUar solubilization sites of aromatic substrates and reaction intermediates are more HzO-rich than those of aliphatic systems. 

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