Indium-Promoted Acyloxyallylation Reaction of Azetidine-2,3-diones in Aqueous Media: A New Route to Densely Functionalized 3-Substituted 3-Hydroxy-β-lactams
Denselyfunctionalized3-substituted3-hydroxy-β-lactams have been obtained by acyloxyallylationreaction of azetidine-2,3-diones with 3-bromopropenyl acetate or benzoate in aqueousmedia promoted by indium under Barbier conditions. Two new stereocenters were formed; the stereochemistry at the new C-3 quaternary center was fully controlled by placing a bulky chiral substituent at C-4. However, poor
A methodology for the direct preparation of bridged acetals from acetonide-tethered alkynes under gold catalysis in the presence of water has been developed. The bicyclic ring structures bearing a bridged five-membered ring arise from the regioselective bis-oxycyclization by initial attack of the oxygen atom to the internal alkyne carbon. (C) 2012 Elsevier Ltd. All rights reserved.
Structurally Novel Bi- and Tricyclic β-Lactams via [2 + 2] Cycloaddition or Radical Reactions in 2-Azetidinone-Tethered Enallenes and Allenynes
[GRAPHICS]Thermolysis of beta-lactam-tethered enallenyl alcohols gave tricyclic ring structures via a formal [2 + 2] cycloaddition of the alkene with the distal bond of the allene, while the tin-promoted radical cyclization in 2-azetidinone-tethered allenynes proceeded to provide bicyclic beta-lactams containing a medium-sized ring. The access to cyclization precursors was achieved by regio- and stereoselective metal-mediated carbonyl allenylation of 4-oxoazetidine-2-carbaldehydes in an aqueous environment.
Reverse-Cope elimination versus 1,3-dipolar cycloaddition in the reaction of enantiopure 2-azetidinone-tethered alkynylaldehydes with N-methylhydroxylamine
作者:Benito Alcaide、Elena Sáez
DOI:10.1016/s0040-4039(00)00006-x
日期:2000.3
Enantiopure 2-azetidinone-tethered alkynylaldehydes 1 react stereoselectively under mild conditions with N-methylhydroxylamine to yield products derived from either intramolecular reverse-Cope elimination or 1,3-dipolar cycloaddition, depending on both the length of the tether and the experimental conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.