A General Method for the Vinylation of Nitrones. Synthesis of Allyl Hydroxylamines and Allyl Amines
摘要:
An examination of the vinylation of several nitrones is presented. Whereas a complete diastereofacial discrimination was observed upon the addition of vinyl organometallic reagents to alpha-alkoxy nitrones, the same reaction with alpha-amino nitrones pave syn adducts in all cases, with the only exception of a L-serine-derived alpha-amino monoprotected nitrone. The obtained allyl hydroxylamines were easily transformed into synthetically valuable allyl amines.
A General Method for the Vinylation of Nitrones. Synthesis of Allyl Hydroxylamines and Allyl Amines
摘要:
An examination of the vinylation of several nitrones is presented. Whereas a complete diastereofacial discrimination was observed upon the addition of vinyl organometallic reagents to alpha-alkoxy nitrones, the same reaction with alpha-amino nitrones pave syn adducts in all cases, with the only exception of a L-serine-derived alpha-amino monoprotected nitrone. The obtained allyl hydroxylamines were easily transformed into synthetically valuable allyl amines.
Stereoselective Addition of 2-Furyllithium and 2-Thiazolyllithium to Sugar Nitrones. Synthesis of Carbon-Linked Glycoglycines
作者:Alessandro Dondoni、Federico Junquera、Francisco Luis Merchán、Pedro Merino、Marie-Christine Scherrmann、Tomas Tejero
DOI:10.1021/jo970290a
日期:1997.8.1
A route to epimeric carbon-linked glycoglycines that exploits the stereoselective addition of 2-lithiofuran and 2-lithiothiazole to sugar nitrones has been described. The reaction occurs with opposite diastereofacial selectivity depending on whether the free nitrone or the diethyl aluminum chloride precomplexed derivative is employed. The resulting furyl or thiazolyl hydroxylamines are dehydroxylated to amines by the action of titanium(III) chloride. From these compounds the amino acids are revealed by the oxidative cleavage of the furan ring or by the conversion of the thiazole into the formyl group and oxidation to carboxylic acid. Compounds have been prepared wherein the alpha-amino acid moiety is installed at C-4 and C-1 of furanoses (ribo, manno, xylo, and lyxo) and at C-5 and C-1 of a pyranose (galacto).