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 |
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Authors: | Valeria Di Bussolo |
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Affiliation: | Dipartimento di Chimica Bioorganica e Biofarmacia, Università di Pisa, Via Bonanno 33, 56126 Pisa, Italy |
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Abstract: | The new 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 addition reactions 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 and partially protected monosaccharides) and C-nucleophiles (alkyl lithium compounds and TMSCN), indicated that a 6-OR group in the side chain is not necessary for determining the selectivity. The reaction of 8α and 8β with azide (TMSN3, N-nucleophile) made it possible to revise a previously proposed rationalization for the formation of the corresponding cis-azido alcohol (syn-1,2-addition product). |
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