en
Scientific article
English

Pi-facial diastereoselection in [4+2]-cycloadditions of 3,4-epoxy-2-methyleneoxolanes with oxadienes : a short synthesis of spiroketals

Published inTetrahedron, vol. 50, no. 27, p. 8035-8052
Publication date1994
Abstract

Hetero Diels-Alder reaction of oxadienes with 3,4-epoxy-2-methyleneoxolanes gave the corresponding 3,4-epoxy-1,6-dioxaspiro[4,5]-dec-7-enes with high stereoselectivity. Good yields of adducts were obtained in the presence of mild Lewis acis, such as zinc or stannous chloride. The spiroketal adducts have been transformed chemio- and stereospecifically by either hydrogenation, hydride reduction or acid catalyzed isomerization. The stereochemical outcome of the cycloadditions has been investigated. The spiroketal adducts always result from an oxadiene addition anti relative to the allylic epoxy substituent. When the oxadiene is substituted suitably as in crotonaldehyde, we demonstrated that the cycloaddition is totally endo selective relative to the enol ether function. Ab initio calculations suggested that 3,4-epoxy-2-methyleneoxolane and 3,4-epoxy-3-methyl-2-methyleneoxolane adopt envelopw conformations with the oxygen atom of the oxolane moiety pointing toward the epoxide ring. No significant distortion from planarity was calculated for the exocyclic double bond of these dienophiles

Affiliation Not a UNIGE publication
Citation (ISO format)
PALE, P. et al. Pi-facial diastereoselection in [4+2]-cycloadditions of 3,4-epoxy-2-methyleneoxolanes with oxadienes : a short synthesis of spiroketals. In: Tetrahedron, 1994, vol. 50, n° 27, p. 8035–8052. doi: 10.1016/s0040-4020(01)85288-1
Identifiers
ISSN of the journal0040-4020
406views
0downloads

Technical informations

Creation08/06/2010 10:46:50 AM
First validation08/06/2010 10:46:50 AM
Update time03/14/2023 3:56:27 PM
Status update03/14/2023 3:56:27 PM
Last indexation01/15/2024 9:02:44 PM
All rights reserved by Archive ouverte UNIGE and the University of GenevaunigeBlack