Glycosylidene Carbenes. Part 6. Synthesis of alkyl and fluoroalkyl glycosides
作者:Karin Briner、Andrea Vasella
DOI:10.1002/hlca.19920750218
日期:1992.3.18
55% of the imidate 10. Glycosidation of di-O-isopropylideneglucose 15 leads to 16 (CH2Cl2, r.t.; 65%, α-D/ β-D = 33:67). That glycosidation occurs by initial protonation of the intermediate glycosylidene carbene is evidenced, for strongly acidic alcohols, by the formation of 10, derived from the attack of (CF3)2MeCO− on an intermediate nitrilium ion (Scheme 4), and for weakly acidic alcohols, by the
描述了在热和/或光解条件下,来自二嗪1的糖苷和一系列醇的合成。产率和非对映选择性取决于醇,溶剂和反应温度的p K HA值。室温下,CH 2 Cl 2中的弱酸性醇(MeOH,EtOH,i-PrOH和t - BuOH,各1当量)的糖基化导致糖苷2–5的收率介于60%至34%之间(方案1和表1)。在-70至-60°时,产率明显更高。在CH 2 Cl 2中,非对映选择性非常低。然而,在THF中,在-70至-60°之间,i-PrOH的糖基化导致比率为8:92的α-D-/β-D- 4。酸性更强的醇,例如CF 3 CH 2 OH,(CF 3)2 CHOH和(CF 3)2 C(Me)OH,以及高度氟化的长链醇CF 3(CF 2)5(CH 2)2 OH(11)与CHF 2(CF 2)9 CH 2 OH(13)反应(CH 2 Cl 2,rt)的收率介于73%和85%之间,主要导致β-D-葡萄糖苷β-D- 6至β-D-