Tertiary epoxides

Disubstituted furans (130) can be obtained by treatment of j8-alkoxy- and j8-arylthio-a,j8-unsaturated ketones, for example 3-methoxy-l-phenyI-2-buten-l-one (128) or 3-ethylthio-l-phenyl-2-buten-l-one (129), with dimethylsulfonium methylide (79JHC815, 69TL679). The possible reaction pathway (Scheme 27) shows the initially formed epoxides as rearranging by ring opening at the tertiary epoxide carbon atom. 

No other derivatives of the tertiary cation, such as the aUylic alcohol in the last part, can r formed this way because the rearrangement is too fast. The reaction with PhSe-SePh and NaBH a trick to get this allylic alcohol. The true reagent is PhSe , formed by reduction of the Se-Se bcr. It is very nucleophilic and will attack even the tertiary epoxide to give a selenide. Oxidation to rh selenoxide leads to a fast concerted cis elimination. The intermediate selenide is unstable as wel m very smelly and must be oxidized immediately before it decomposes. 

Ethylene oxide and simple primary and secondary epoxides 271 Tertiary epoxides 272 Acetals and epoxy ethers 272 Vinyl epoxides 273... 

Experiments presently in progress suggest that the mono-tosylate precursors of the terticiry alcohols can alternatively be converted, by base, to primcury-tertiary epoxides which in t im may be opened at the primary site by a variety of nucleophiles, thus greatly amplifying the opportunities for synthesis of compounds bearing chiral tertiary carbinol moieties. It has also proved possible (23, 30) to oxidize the a-hydroxyaldehydes to a-hydroxy-esters which, in turn, may be saponified to a-hydroxyacids. 

Miscelleneous Applications. The method of choice for the regioselective opening of benzylic and tertiary epoxides with alcohols (eq 13) appears to be a reaction mediated by organ-otin phosphate condensate (OPC) , which is readily prepared from DBTO and tributyl phosphate. DBTO catalyzes rearrangement of 3-hydroxy-2-oxo carboxylic acid esters (eq 14), a reaction reminiscent of a similar one mediated by the enzyme reductoisomerase. DBTO has been used as a catalyst for the addition of Azidotrimethylsilane to nitriles for the production of tetrazoles (eq 15). 

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