Stereoselectivity of Triplet Photocycloadditions:<sup>1</sup> Diene−Carbonyl Reactions and Solvent Effects
作者:Axel G. Griesbeck、Stefan Buhr、Maren Fiege、Hans Schmickler、Johann Lex
DOI:10.1021/jo971767l
日期:1998.6.1
The diastereoselectivity of the photocycloaddition of benzaldehyde to furan was determined (exo/endo = 212:1) and compared with the reaction of other carbonyl compounds and carbonyl analogues. These results were compared with Paterno-Buchi reactions of cycloalkenes and cyclic enol ethers. An increase in steric demand of the a-substituent in benzoyl compounds led to a change in exo/endo-selectivity for furan cycloadditions that was not observed for cycloalkenes or cyclic enol ethers. Different ISC-reactive conformers with enhanced spin-orbit coupling are postulated as a reasonable explanation for the stereoselectivities observed. Additionally, solvent effects were studied, demonstrating the influence of photoinduced electron-transfer steps on the regio- and diastereoselectivity of Paterno-Buchi reactions with 2,3-dihydrofuran in polar solvents. Two bicyclic oxetanes (8 and 10) were characterized by X-ray structure analysis.