L-Fucal → 1,5-anhydro-3-oxo-2,3,6-trideoxy-L-threo-hex-1-enitol

In a 250 milliliter round-bottomed flask, 1 gram of L-fucal [Example 5 product] is dissolved in 100 milliliters of benzene. To this solution was added 20-25 grams of silver carbonate on celite (Fetizon's reagent), prepared as described below, and the mixture was stirred. The flask was equipped for simple distillation, and 20-25 milliliters of solvent was removed by distillation. During this time the yellow Fetizon's reagent becomes dark brown. The distillation assembly is replaced with an efficient reflux condenser and the mixture is refluxed for 1 hour, after which time the reaction is generally completed as judged by t.l.c. monitoring. The hot mixture is filtered through celite and the filtrate evaporated under reduced pressure to give 1,5-anhydro-3-oxo-2,3,6-trideoxy-L-threo-hex-1-enitol.