Conjugate addition-rearrangement of N-substituted hydroxylamines to α,β-unsaturated D-lactones provides a short and effective route to 3-substituted isoxazolidin-5-ones. These compounds were converted into 4-substituted azetidin-2-ones via a two-step procedure involving hydrogenolysis of the NO bond followed by cyclization of the resulting β-amino acids. N-Benzyl-4-(3′-acetoxy-2′-tert-butyldimeth
rearrangement of N-benzylhydrazine to sugar δ-enlactone with erythroconfiguration 1 and 2 affords mixtures of respective ribo and arabino isomers with the former one prevailing. In the case of the threo lactone 3 two regioisomers with xylo configuration are produced, whereas in the case of 4 only one isomer with the erythroconfiguration is formed. The stereochemical course of these rections was explained
Cycloaddition of nitrones and α,β-unsaturated sugar lactones
作者:Irma Panfil、Marek Chmielewski
DOI:10.1016/s0040-4020(01)82368-1
日期:1985.1
It was found that 1,3-cycloaddition of nitrones 1–3 to α,β-unsaturated sugar carbonyl compounds 4–8 proceeds regiospecifically to give mixtures of stereoisomers. Nitrones 1–3 entered compounds 4–8 in trans-relation to the existing ring substituent.
1,3‐Dipolar cycloaddition of nitrones 1–3 to the α,β‐unsaturated δ‐lactones, non‐chiral 4, d‐glycero 5, dl‐glycero 5/5ent, d‐erythro 6, and d‐threo 7, provides an interesting example of a doubleasymmetricinduction. In all cases, only the exo approach of reactants was observed. The high preference of anti addition of the nitrones to the terminal acetoxymethyl group in the lactones 5–7 is consistent
Conjugate addition-rearrangement of N-benzylhydroxylamine to α,β-unsaturated lactones 1 provides a short and effective route to 3-substituted isoxazolidin-5-ones. High and defined stereochemistry of this reaction with simultaneous liberation of the 5-OH group of the sugar chain, while all other groups remain protected, creates a possibility to switch from sugars of the D-configurational series to