Contrasting reactivity of thioglucoside and selenoglucoside donors towards promoters: implications for glycosylation stereocontrol.
The stereochemical outcome of glycosylation reactions with model thioglycosides and selenoglycosides proved to be dependent on the source of promoter iodonium ion, with iodine giving different results to N-iodosuccinimide (NIS) alone or N-iodosuccinimide/trimethylsilyltrifluoromethanesulfonate (NIS/TMSOTf). In contrast to armed thioglycosides, which anomerise, and disarmed thioglycosides, which do not react, both armed and disarmed selenoglycosides give rise to the corresponding glycosyl iodides when reacted with iodine. Further, whilst the single electron transfer agent DDQ alone is an ineffective promoter, in combination with iodine it produces better acetonitrile-assisted beta-stereoselectivity with both thioglycosides and selenoglycosides than does tris(4-bromophenyl)aminium hexachloroantimonate (BAHA).
van Well
Renate M
RM
Centre for Carbohydrate Chemistry, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK.
Kärkkäinen
Tiina S
TS
Kartha
K P Ravindranathan
KP
Field
Robert A
RA
D016227:Benzoquinones / Q000737:chemistry; D004579:Electron Transport; D005960:Glucosides / Q000737:chemistry*; D006031:Glycosylation; D007455:Iodine / Q000737:chemistry; D008698:Mesylates / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D009942:Organometallic Compounds / Q000737:chemistry; D016566:Organoselenium Compounds / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D013237:Stereoisomerism; D013388:Succinimides / Q000737:chemistry; D013863:Thioglucosides / Q000737:chemistry*; D014297:Trimethylsilyl Compounds
D016227:Benzoquinones; D005960:Glucosides; D008698:Mesylates; D009942:Organometallic Compounds; D016566:Organoselenium Compounds; D000644:Quaternary Ammonium Compounds; D013388:Succinimides; D013863:Thioglucosides; D014297:Trimethylsilyl Compounds; C079938:tris(4-bromophenyl)ammoniumyl hexachloroantimonate; C000928:dichlorodicyanobenzoquinone; C053353:trimethylsilyl trifluoromethanesulfonate; C008155:N-iodosuccinimide; D007455:Iodine