Allyl protecting group mediated intramolecular aglycon delivery: optimisation of mixed acetal formation and mechanistic investigation
摘要:
An efficient protocol for the formation of alpha-iodo mixed acetals, the first step of allyl-mediated 1AD, by reaction of allyl-derived enol ethers and alcohols, using I-2, AgOTf and di-tert-butyl methylpyridine as a novel source of I+, is reported. This reagent combination is capable of tethering glycosyl donors to the secondary alcohol groups of a variety of glycosyl acceptors including mono-, di- and trisaccharides. Mechanistic studies confirm the intramolecular nature of the glycosylation reaction, whilst the attempted use of diol glycosyl acceptors reveals limitations of both regio- and stereo selectivity in the glycosylation step. (C) 2004 Elsevier Ltd. All rights reserved.