RxN of the anomeric center Il
RXN$of$the$anomeric$center$II$
Brief review of mutarotation andfuranose/pyranose inter-conversionOHH+BaseO.O-HHCHOOHOHHO'OHHOOHHObondHOHO'OH43HO"4'OHrotationOHHOOHOHOHOHOOHHO'OHOHHOOH
Brief$review$of$mutarota5on$and$ furanose/pyranose$inter;conversion$ OH O OH HO OH 5 1 4 3 2 HO 6 bond rotation O HO OH OH HO HO 1 2 3 4 5 6 O O OH HO OH HO ! H Base H+ O OH OH HO OH HO ! O OH HO OH OH HO ! O OH HO OH OH HO !
1. Nucleophilic substitution at anomericcentreGlycosylationGlycosidicDonerAcceptorBonda(RO)n(RO)n(RO)nto0ELNU-HLgSubstitutionActivationLg:Nu632
Doner Acceptor$ Glycosidic Bond$ Glycosyla(on 1.!Nucleophilic!subs/tu/on!at!anomeric centre
Good leaving groupb(RO)nO(RO)n(RO)n(RO)nO(O)P-OROHF/C/Br/O5746ORHNCCl3Mn+,R2S+-X,MesSi-OTfMn+MegSi-OTf,R3P+-X,ArylSO2-X(halophilic)BF3-OEt2(RO)n(RO)nO(RO)n(RO)nO/S_alkylSEarylH2C)3S/OR/ORI(0)OMeSR/NR2910118H*, Mn+RSt, Br+, I+,Ht, Cu2+Brt, I+Hg2+, R2S+-X,Tf20(oxo-,thio-,azaphilic)Nature2007,446,1000
Nature$2007,$446,$1000$ Good$leaving$group$
Stereochemistryconsideration/S1orS~2ORORRORORORCORORRingoxygenfacilitatesS1typepathwaysAidthedepartureofleavinggroupandstabilisethecarboniumionintermediate0ndonationAnomericeffect
Stereochemistry!considera/on/!SN1!or!SN2! O OR RO RO OR L O OR RO RO OR Ring!oxygen!facilitates!SN1!type!pathways! O n !" n !" donation Aid!the!departure!of!leaving!group!and!! stabilise!the!carbonium!ion!intermediate! Anomeric!effect!