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- Title
Minimally Competent Lewis Acid Catalysts: Indium(III) and Bismuth(III) Salts Produce Rhamnosides (=6-Deoxymannosides) in High Yield and Purity.
- Authors
Coss, Clifford; Carrocci, Tucker; Maier, Raina M.; Pemberton, Jeanne E.; Polt, Robin
- Abstract
Glycosylation of decan-1-ol ( 2), (±)-decan-2-ol ( 3), and (±)-methyl 3-hydroxydecanoate ( 4) with L -rhamnose peracetate 5 to produce rhamnosides (=6-deoxymannosides) 6, 7, and 8 in the presence of Lewis acids BF3⋅Et2O, Sc(OTf)3, InBr3, and Bi(OTf)3 was studied ( Table 1). While the strong Lewis acids BF3⋅Et2O and Sc(OTf)3 were effective as glycosylation promoters, they had to be used in excess; however, glycosylation required careful control of reaction times and temperatures, and these Lewis acids produced impurities in addition to the desired glycosides. Enantiomerically pure rhamnosides ( R)- 1 and ( S)- 1 ( Fig.) were obtained from L -rhamnose peracetate 5 and (±)-benzyl 3-hydroxydecanoate ( 9) via the diastereoisomeric rhamnosides 10 ( Table 2; Scheme 3). The much weaker Lewis acids InBr3 and Bi(OTfl)3 produced purer products in high yield under a wider range of conditions (higher temperatures), and were effective glycosylation promoters even when used catalytically (<10% catalyst; Table 2). We refer to these Lewis acids as 'minimally competent Lewis acids' ( cf. Scheme 4).
- Subjects
LEWIS acids; CATALYSTS; CATALYSIS; INDIUM; BISMUTH; GLYCOSYLATION; RHAMNOSIDES
- Publication
Helvetica Chimica Acta, 2012, Vol 95, Issue 12, p2652
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/hlca.201200528