The mechanism of the diastereoselection in the photosensitized [2 + 2]-cycloaddition reaction of ethylene to 5-alkoxy-2(5H)-furanones is investigated. The dependence of product ratio on the reaction temperature as well as on structural features of the enone system is measured. The structure dependent activation parameter differences (Delta Delta H-#, Delta Delta S-#) obtained by this method (modified Eyring plot) are used as a tool to characterize the stereoelectronic factors, which are responsible for the diastereoselection. In detail these factors involve: pyramidalization of the beta-carbon, homoanomeric effect, and the steric requirements of the alkoxy substituent in the relaxed ((3) pi pi*)-excited furanones.
Towards the catalytic formation of α,β-vinylesters and alkoxy substituted γ-lactones
作者:Pradeep Mathur、Raj Kumar Joshi、Badrinath Jha、Amrendra K. Singh、Shaikh M. Mobin
DOI:10.1016/j.jorganchem.2010.08.036
日期:2010.11
A facile, one pot, high yield synthesis of α,β-vinylester (1–14) and alkoxy substitutedγ-lactones (15–28) has been achieved by the photochemical reaction of terminal acetylene (ferrocenyl phenyl trimethylsillyl, hexyl and cyclohexyl) with alcohol (methanol, ethanol and isopropanol) and carbon monoxide in presence of iron pentacarbonyl as a catalyst. The selectivity of the compounds depends on the