Showing papers by "Leo A. Paquette published in 2005"
TL;DR: An enantioselective approach to 2'-deoxy-4'-thia spirocyclic nucleosides featuring an alpha- or beta-hydroxyl substituent at C-5' of the carbocyclic ring is detailed, and various 1D and 2D NMR techniques are used for assigning configuration.
Abstract: An enantioselective approach to 2‘-deoxy-4‘-thia spirocyclic nucleosides featuring an α- or β-hydroxyl substituent at C-5‘ of the carbocyclic ring is detailed. The starting point is the mandelate a...
46 citations
TL;DR: There is a highly practical and reliable means for the formation of novel 2'-deoxyribonucleosides of novel structural type from these spirocyclic cyclopentenones.
Abstract: The levorotatory diol 7 has been sequentially monosilylated, dehydrated, and oxidized at the allylic methylene group to provide (+)-12. The enantiomeric dextrorotatory diol 7 has been directed down a different sequence of steps involving monosilylation, dehydration, hydroboration, Swern oxidation, and regioselective introduction of a conjugated double bond to generate (-)-33. The novel feature of these transformations is that two key deoxycarbospironucleoside intermediates of the proper absolute configuration have been made available from enantiomerically related precursors. Also reported is a highly practical and reliable means for the formation of novel 2'-deoxyribonucleosides of novel structural type from these spirocyclic cyclopentenones.
17 citations
TL;DR: Two approaches for the conversion of d-glucose to (−)-neplanocin A (2), both based on the zirconocene-promoted ring contraction of a vinyl-substituted pyranoside, are described in this article.
Abstract: Two approaches for the conversion of d-glucose to (−)-neplanocin A (2), both based on the zirconocene-promoted ring contraction of a vinyl-substituted pyranoside, are herein evaluated (Scheme 1). In the first pathway (Scheme 2), the substrate possesses the α-d-allo configuration (see 6) such that ultimate introduction of the nucleobase would require only an inversion of configuration. However, this precursor proved unresponsive to Cp2Zr (=[ZrCl2(Cp)2]), an end result believed to be a consequence of substantive nonbonded steric effects operating in a key intermediate (Scheme 5). In contrast, the C(2) epimer (see 7) experienced the desired metal-promoted conversion to an enantiomerically pure polyfunctional cyclopentane (see 5 in Scheme 3). The substituents in this product are arrayed in a manner such that conversion to the target nucleoside can be conveniently achieved by a double-inversion sequence (Scheme 4). Recourse to palladium(0)-catalyzed allylic alkylation did not provide an alternate means of generating 2.
14 citations
TL;DR: The ability of methyl(trifluoromethyl)dioxirane to cleave p-methoxylbenzyl ethers oxidatively in the presence of various additional functional groups has been investigated and transform a reasonably robust aryl substituent into a dienyl aldehydo ester.
7 citations
TL;DR: In this article, an enantioselective approach to 2'deoxy-4'thia spirocyclic nucleosides featuring an α- or β-hydroxyl substituent at C-5' of the carbocyclic ring is described.
Abstract: An enantioselective approach to 2‘-deoxy-4‘-thia spirocyclic nucleosides featuring an α- or β-hydroxyl substituent at C-5‘ of the carbocyclic ring is detailed. The starting point is the mandelate a...
2 citations
TL;DR: In this paper, the levorotatory diol 7 has been sequentially monosilylated, dehydrated, and oxidized at the allylic methylene group to provide (+)-12.
Abstract: The levorotatory diol 7 has been sequentially monosilylated, dehydrated, and oxidized at the allylic methylene group to provide (+)-12. The enantiomeric dextrorotatory diol 7 has been directed down a different sequence of steps involving monosilylation, dehydration, hydroboration, Swern oxidation, and regioselective introduction of a conjugated double bond to generate (-)-33. The novel feature of these transformations is that two key deoxycarbospironucleoside intermediates of the proper absolute configuration have been made available from enantiomerically related precursors. Also reported is a highly practical and reliable means for the formation of novel 2'-deoxyribonucleosides of novel structural type from these spirocyclic cyclopentenones.
1 citations
TL;DR: Two approaches for the conversion of d-glucose to (−)-neplanocin A (2), both based on the zirconocene-promoted ring contraction of a vinyl-substituted pyranoside, are described in this article.
Abstract: Two approaches for the conversion of d-glucose to (−)-neplanocin A (2), both based on the zirconocene-promoted ring contraction of a vinyl-substituted pyranoside, are herein evaluated (Scheme 1). In the first pathway (Scheme 2), the substrate possesses the α-d-allo configuration (see 6) such that ultimate introduction of the nucleobase would require only an inversion of configuration. However, this precursor proved unresponsive to Cp2Zr (=[ZrCl2(Cp)2]), an end result believed to be a consequence of substantive nonbonded steric effects operating in a key intermediate (Scheme 5). In contrast, the C(2) epimer (see 7) experienced the desired metal-promoted conversion to an enantiomerically pure polyfunctional cyclopentane (see 5 in Scheme 3). The substituents in this product are arrayed in a manner such that conversion to the target nucleoside can be conveniently achieved by a double-inversion sequence (Scheme 4). Recourse to palladium(0)-catalyzed allylic alkylation did not provide an alternate means of generating 2.