Aminolysis of glycal-derived allyl epoxides and activated aziridines. Effects of the absence of coordination processes on the regio- and stereoselectivity
作者:Valeria Di Bussolo、Lorenzo Checchia、Maria Rosaria Romano、Lucilla Favero、Mauro Pineschi、Paolo Crotti
DOI:10.1016/j.tet.2009.11.059
日期:2010.1
The addition of primary and secondary aliphatic amines to glycal-derived allyl epoxides is completely 1,2-regio- and anti-stereoselective, whereas mixtures of the corresponding anti-1,2- [3-N-(substituted-amino) glycals] and anti-1,4-addition products (N-glycosyl amines) are obtained with N-(mesyl)-aziridines. In this way, structural moieties, otherwise difficult to synthesize, are obtained by means of a very simple protocol. The regio- and stereoselectivity observed with epoxides is the consequence of an isomerization process, whereas the result obtained with aziridines is explained by the absence of an effective substrate-nucleophile (amine) coordination. (C) 2009 Elsevier Ltd. All rights reserved.
A novel glycosyl donor for synthesis of 2-acetamido-4-amino-2,4,6-trideoxy-α-d-galactopyranosides
作者:Ithayavani Iynkkaran、David R. Bundle
DOI:10.1016/j.carres.2010.08.017
日期:2010.11
2-Azido-4-benzylamino-4-N-,3-O-carbony1-2,4,6-trideoxy-D-galactopyranosyl trichloroacetimidate (14) was conveniently prepared in six steps by regioselective introduction of an N-benzyl carbamate at O-3 of 6-deoxy-D-glucal 6, followed by mesylation at O-4. Intramolecular displacement of the leaving group afforded oxazolidinone 11. Azidonitration of the bicyclic glycal 11 gave the glycosyl nitrate anomers 12 in good yield and stereoselectivity. Hydrolysis of the anomeric nitrates under aqueous conditions gave the pyranose 13, which was easily converted into the imidate 14. Glycosylation of cyclohexanol by 14 gave glycosides 16 alpha and 16 beta in a ratio of 4:1. (C) 2010 Elsevier Ltd. All rights reserved.
Synthesis of diastereoisomeric 6-deoxy-d-allal- and 6-deoxy-d-galactal-derived allyl epoxides and examination of the regio- and stereoselectivity in nucleophilic addition reactions. Comparison with the corresponding 6-O-functionalized allyl epoxides
作者:Valeria Di Bussolo、Lucilla Favero、Maria Rosaria Romano、Mauro Pineschi、Paolo Crotti
DOI:10.1016/j.tet.2008.06.039
日期:2008.8
6-deoxy-d-allal- and 6-deoxy-d-galactal-derived allyl epoxides 8α and 8β have been stereoselectively prepared and their behaviour as glycosyl donors in additionreactions with nucleophiles examined and compared with that of the corresponding 6-OR (R=Bn, Tr) substituted epoxides. The completely stereoselective substrate-dependent glycosylation process found in the reaction of 8α and 8β with O-nucleophiles (alcohols