Aluminum epoxide ring

Ethyl 2,3-epoxypropanoate is a very interesting chiron. It may be opened by various organometallic compounds such as dialkyl, diaryl, and divinyl lithium cuprates, dialkylmagnesium cuprates, trialkylalanes and aluminum acetylides.5 6 The epoxide ring is attacked regiospecifically at the p-position and produces a-hydroxy esters exclusively without racemization. The same result is observed with... 

Lithium aluminum hydride opens the epoxide ring reductivcly... 

Ascarylose (94) and the (35) deuterium-labeled ascarylose were prepared starting from methyl a-L-rhamnopyranoside via the 2,3-anhydro sugar 120 (Scheme 34).204 Opening of the epoxide ring with lithium aluminum hydride in THF led selectively to the 3-deoxy derivative. If reduction was performed with lithium aluminum deuteride, the methyl (3S)-[32H]ascaryloside (3S)-[32H]119 was obtained. 

On nucleophilic attack, the epoxide ring opens according to the Furst-Plattner rule, with the formation of the di-axial derivative, because the pyranoid rings in the frons-linked derivatives (98) and (99) are completely fixed and the cfs-linked derivatives (100) and (101) are fixed to a considerable extent in the Cl form. (The corresponding members of the L series belong to the 1C form ) The 2-deoxy derivatives are prepared by the mercaptal method, and also, more easily, by direct reduction of the anhydro derivatives (98) and (100) with lithium aluminum hydride. Only the riho and xylo configurations, (102) and (104), are accessible (X = H), but these are obtained in very good yield. This... 

The trithiocarbonates may prove useful as intermediates for the synthesis of sugar dithiols from epoxides. Ring opening by reductive cleavage with lithium aluminum hydride gives excellent results with aliphatic and ahcyclic trithiocarbonates. When both carbon atoms are secondary, the product is a iraws-dithiol for example, cyclohexene oxide, which is converted into a irans-trithiocarbonate, gives, on reduction, cyclo-hexane-1,2-dithiol. The reaction has been used in the cyclitol series for the preparation of 1,2-dithio-neo-inositol and 1,2-dithio-ir-inositol, from 1,2-anhydro-alZo-inositol. The inositol trithiocarbonates show pronounced Cotton effects in their optical rotatory-dispersion spectra. 

The reductive ring opening of 330a with sodium cyanoborohydride/titanium tetrachloride in acetonitrile occurs with no ester reduction whatsoever to provide 421 in 83% yield. Subsequent conversion to the tosylate followed by reduction with lithium borohydride/lithium triethylborohydride affords in 61% yield the crystalline diol 422. Lithium aluminum hydride or sodium borohydride reduction of the tosylate of 421 fails to produce clean reductions to 422. Epoxide ring closure of 422 is achieved with two equivalents of sodium hydroxide in methanol to fiimish in 93% yield (2 S, 3i )-2-benzyloxy-3,4-epoxybutan-l-ol (423) [140] (Scheme 94). 

When the epoxide (presumably the a-form, XXXIV) is reduced with lithium aluminum hydride in ether-benzene and the reaction product reacetylated with acetic anhydride-pyridine, there is formed an 0,0 -diacetyl-W-ethylhydroxydihydroveratramine (XL), which readily loses water in contact with thionyl chloride-pyridine to generate an 0,0 -diacetyl-iV-ethylveratramine (XLI). During this reduction there is also formed a product which on reacetylation proved to be 0,0 -diacetyl-iV-ethyldihydroxydihydroveratramine (XLII). Its structure is uncertain but it appears to be formed by hydrolytic rather than reductive cleavage of the epoxide ring (42). 

Epoxide Ring Opening. v s a result of its Lewis acidity, several reaction pathways are followed in the reductive ring opening of epoxides by DIBAL. Attack at the more hindered carbon via carbenium ion-like intermediates (see also Aluminum Hydride)... 

Oxidation of cyclohexene by a peroxyacid (Section 11.8Q gives an epoxide. Stereoselective nucleophilic attack by azide ion anti to the leaving oxygen of the epoxide ring (Section 11.9B) followed by reduction of the azide with lithium aluminum hydride gives racemic fra s-2-aminocyclohexanol. 

Reductive scission of the epoxide ring to produce deoxysugars may be accomplished by catalytic hydrogenation or with lithium aluminum hydride (87) ... 

The reactions of Grignard reagents and lithium aluminum hydride with epoxides are regioselective in the same sense as the examples just shown. Substitution occurs at the less substituted carbon of the epoxide ring. 

---