Abstract
The dithionite-mediated chlorodifluoromethylations of 3,4-di-O -acetyl-1,5-anhydro-2,6-dideoxy-l -arabino -hex-1-enitol (1 ), 1,5-anhydro-2,3,4-tri-O -pivaloyl-d -erythro -pent-1-enitol (13 ), 2,3,4-tri-O -acetyl-1,5-anhydro-6-deoxy-l -lyxo -hex-1-enitol (15 ), and 2,3,4,6-tetra-O -acetyl-1,5-anhydro-d -arabino -hex-1-enitol (18 ) with CBrClF2 in acetonitrile-water and methanol, respectively, are described. Sodium dithionite serves as radical initiator and reducing reagent. Whereas, starting with 1 , the chlorodifluoromethyl group was predominantly introduced into position 2, the 1-chlorodifluoromethyl substituted C -glycosides 1,5-anhydro-1-(S )-chlorodifluoromethyl-2,3,4-tri-O -pivaloyl-d -ribitol (14 ), 2,3,4-tri-O -acetyl-1,5-anhydro-1-(R )-chlorodifluoromethyl-6-deoxy-l -galactitol (16 ), and 2,3,4,6-tetra-O -acetyl-1,5-anhydro-1-(S )-chlorodifluoromethyl-d -glucitol (19 ) could be synthesized in moderate to good yields from 13 , 15 , and 18 , respectively. X-ray analyses are given for the products 3,4-di-O -acetyl-1,5-anhydro-2-chlorodifluoromethyl-2,6-dideoxy-l -glucitol, 1,3,4-tri-O -acetyl-2-chlorodifluoromethyl-2,6-dideoxy-α-l -mannopyranose, 1,5-anhydro-1-(S )-chlorodifluoromethyl-2,3,4-tri-O -pivaloyl-d -ribitol, and 2,3,4,6-tetra-O -acetyl-1,5-anhydro-1-(S )-chlorodifluoromethyl-d -glucitol.
Key words
carbohydrates - glycals - radical reactions - additions - chlorodifluoromethylations
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