A new route to some enantiomerically pure substituted morpholines from d-ribono- and d-gulono-1,4-lactones

d-Ribono-1,4-lactone, after acetalation, tritylation, and reduction, leads to a cyclization compound which gave with tosyl chloride 1,4-anhydro-2,3-O-isopropylidene-5-O-trityl-d-ribitol. The latter was transformed (acid hydrolysis, periodate oxidation, reduction, tritylation, and tosylation) into a ditosylated derivative 16, which was cyclized into morpholines by the action of primary amines. Acid hydrolysis, followed by acetylation, gives the (2S)-acetoxymethyl-4-isopropyltetrahydro-1,4-oxazine (21). A similar sequence has been applied to d-gulonolactone to give access to oxazines 33, 34, and 35.