Fused bicyclic 4-pyrones were prepared by condensation of enamines derived from cyclic ketones with diketene or substituted 1,3-dioxin-4-ones. Photolysis in a hydroxylic medium led to bicyclo[n3.0]alkenones bearing oxygenation at both angular positions. This process is occurs via regioselective nucleophilic solvent attack on the intermediate tricyclic oxyallyl zwitterion. The efficiency of the transformation
Solvent Trapping of Photochemically Generated Pyran-4-one-Derived Oxyallyls: A Convenient Cyclopentannulation Method
作者:Frederick West、Mike Fleming、Peter Fisher、Gamini Gunawardena、Yinghua Jin、Chen Zhang、Wei Zhang、Atta Arif
DOI:10.1055/s-2001-15067
日期:——
irradiation in aqueous H2SO4 gave the corresponding glycols 8 and 9. The unusual predominance of cis-fused product 8b appears to result from in situ acid-catalyzed equilibration. Substrate 2f could also be trapped in aqueous acid, and displayed a modest stereoselectivity that may derive from conformational control by the methyl group on the starting material’s stereogenic center.