(2S,3R,4S)-2-methyl-3,4-dihydro-2H-pyran-3,4-diol → 1,5 anhydro-2,6-dideoxy-L-erythro-hex-1-en-3-ulose

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Reaction Steps

When Fetizon's reagent is used, L-rhamnal is dissolved in benzene and then the Fetizon's reagent is added to the mixture (20 g reagent: 1 g L-rhamnal). The mixture is refluxed for 1 hour, the spent reagent removed by filtration, and the solvent removed by evaporation to yield nearly pure enone. When the oxidant is chromium trioxide:pyridine complex, L-rhamnal is added to a solution of the oxidant in dichloromethane followed by addition of 4 equivalents of acetic anhydride. After 20 minutes the reaction mixture is poured onto a column of silica gel (ethyl acetate eluent) containing excess ethyl acetate at the top to precipitate insoluble chromium compounds. The product is eluted with ethyl acetate. If manganese dioxide is used, L-rhamnal is dissolved in tetrahydrofuran and treated with active manganese dioxide (15 g MnO2 : 1 g L-rhamnal) and stirred at room temperature for 2-3 days. The oxidant is then removed by filtration and the product purified by chromatography on a silica gel column (ethyl acetate eluent).

Provenance & Evidence