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C‐Glycosidations of a 2‐Ketohexosyl Bromide with Electrophilic, Radical, and Nucleophilic Anomeric Carbons
Author(s) -
Lichtenthaler Frieder W.,
Lergenmüller Matthias,
Schwidetzky Sabine
Publication year - 2003
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200300152
Subject(s) - chemistry , anomer , nucleophile , electrophile , medicinal chemistry , trifluoromethanesulfonate , cyanohydrin , organic chemistry , catalysis
The susceptibility of acylated 2‐ketohexosyl halides to C‐homologation is demonstrated with the easily accessible tri‐ O ‐benzoyl‐α‐ D ‐ arabino ‐hexos‐ulosyl bromide 1 as the model compound. C‐Glycosidation with an electrophilic anomeric carbon requires prior carbonyl protection, to avoid carbonyl addition by the C‐nucleophile, for example, as the cyanohydrin. Silver triflate‐promoted reaction with the silylenol ether of acetophenone then efficiently yields the β‐phenacyl product. With thermal (AIBN) or photochemical induction, 1 smoothly generates an anomeric radical − comparatively electrophilic, due to its capto‐dative substitution − which exclusively traps hydrogen in the presence of tributyltin and electron‐deficient alkenes. With allyltributylstannanes, however, it reacts with high stereoselectivity to afford α‐ C ‐allyl glycosiduloses. The α‐bromoketone functionality in ulosyl bromide 1 is susceptible to Reformatsky conditions: treatment with zinc‐copper couple readily generates the 1,2‐enolate, a most simple anomeric nucleophile, which effectively adds to aldehydes to give α‐ C ‐hydroxyalkyl glycosiduloses or α‐ C ‐disaccharides (with sugar aldehydes) with a high degree of double stereoselection. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)