Stereocontrol by diethylaluminum chloride in the addition of 2-lithiofuran and N-methyl-2-lithioimidazole to α-alkoxy nitrones. Total synthesis of 5-O-carbamoylpolyoxamic acid.
作者:Alessandro Dondoni、Santiago Franco、Francisco Luis Merchán、Pedro Merino、Tomás Tejero
DOI:10.1016/s0040-4039(00)73939-6
日期:1993.1
derived from D-glyceraldehyde acetonide leads to the corresponding syn-adducts as major products (ds 88–96 %) while the reaction in the presence of Et2AlCl leads to anti isomers (ds 79–95 %); the synthesis of 5-O-carbamoylpolyoxamicacid from 4-O-benzyl-2,3-O-isopropylidene-L-threose via the nitrone-furan adduct is described
Addition of 2-Lithiofuran to Chiral α-Alkoxy Nitrones; a Stereoselective Approach to α-Epimeric β-Alkoxy-α-amino Acids
作者:A. Dondoni、F. Junquera、F. L. Merchan、P. Merino、T. Tejero
DOI:10.1055/s-1994-25712
日期:——
The addition of 2-lithiofuran (1) to the N-benzyl nitrones 2a-d, derived from chiral α-alkoxy aldehydes, affords β-alkoxy-α-hydroxyamino-2-alkylfurans in good yields and with syn selectivity. Conversely, the reaction with the same nitrones precomplexed with diethylaluminum chloride leads to the same adducts but with anti selectivity. Three pairs of epimeric hydroxylamines are subjected to reductive N-dehydroxylation with titanium(III) chloride and then to furyl-carboxylic acid conversion with ruthenium tetroxide to give the corresponding α-epimeric β-alkoxy-α-amino acids.
Addition of lithiated enol ethers to nitrones and subsequent Lewis acid induced cyclizations to enantiopure 3,6-dihydro-2<i>H</i>-pyrans – an approach to carbohydrate mimetics
作者:Fabian Pfrengle、Hans-Ulrich Reissig
DOI:10.3762/bjoc.6.75
日期:——
A stereodivergent synthesis of enantiopure 3,6-dihydro-2H-pyrans is presented. The addition of lithiated enol ethers to carbohydrate-derived nitrones afforded syn- or anti-configured hydroxylamine derivatives 4a-d that were cyclized under Lewisacidic conditions to yield functionalized dihydropyrans cis- or trans-5a-d containing an enol ether moiety. This functional group was employed for a variety