Organofluorine Compounds and Fluorinating Agents, Part 33: [1] Regioselective Chlorodifluoromethylations in the 1-Position of 1,2-Unsaturated Monosaccharide Derivatives

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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Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 258180-258183. Copies of these data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: [phone] or e-mail: [e-mail]) or via www.ccdc.cam.ac.uk/conts/retrieving.html.