Epoxides, ring opening reactions sugar synthesis

In a series of papers, the application of titanium alkoxide catalysts to the synthesis of sugars has been described. Asymmetric epoxidation and kinetic resolution of (48) afforded (+)-(49) (27% >95%e.e.) and (—)-(48) (33% 72%e.e.). The ring-opening reactions of the chiral epoxides that are produced, for example, from cis- and from trans- 50) provide new routes to saccharides. The reagents also find use in the synthesis of pheromones e.g., (+)-disparlure and (+)-2,6-dimethylhepta-l,5-dien-3-ol acetate via the epoxide (52), which was obtained from the dienol (51) by using D-(—)-... 

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. 

Nucleophilic ring opening of epoxy sugars is a valuable method for the synthesis of many modified sugar derivatives. The reaction is accompanied by Walden inversion, and a wide range of nucleophiles can be used. The cyclic nature of epoxides renders the competing elimination process stereoelectronically unfavourable. For asymmetric epoxides, in principle, two regio-isomeric products can be formed however, in... 

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