ISSN:
0018-019X
Schlagwort(e):
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The regio- and stereoselectivity of the glycosidation of the partially protected mono-alcohols 3 and 7, the diols 2 and 8, and the triol 4 by the diazirine 1 have been investigated. Glycosidation of the α-D-diol 2 (Scheme 2) gave regioselectively the 1,3-linked disaccharides 11 and 12 (80%, α-D/β-D 9:1), whereas the analogous reaction with the βD-anomer 8 led to a mixture of the anomeric 1,3- and 1,4-linked disaccharides 13 (12.5%), 14 (16%), 15 (13%), and 16 (20.5%; Table 2). Protonation of the carbene by OH-C(4) of 2 is evidenced by the observation that the α-D-mono-alcohol 3 did not react with 1 under otherwise identical conditions, and that the β-D-alcohol 7 yielded predominantly the β-D-glucoside 18 (52%) besides 14% of 17. Similarly as for the glycosidation of the diol 2, the influence of the H-bond of HO—C(4) on the direction of approach of the carbene, the role of HO—C(4) in protonating the carbene, and the stereoelectronic control in the interception of the ensuring oxycarbenium cation are evidenced by the reaction of the triol 4 with 1 (Scheme 3), leading mostly to the α-D-configurated 1,3-linked disaccharide 19 (41%), besides its anomer 20 (16%), and some 4-substituted β-D-glucoside 21 (9%). No 1,6-linked disaccharides could be detected. In agreement with the observed reactivity, the 1H-NMR and IR spectra reveal a strong H-bond between HO—C(3) and the phthalimido group in the α-D-, but not in the β-D-allosides. The different H-bonds in the anomeric phthalimides are in keeping with the results of molecular-mechanics calculations.
Zusätzliches Material:
4 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/hlca.19940770724
