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Download fileStereoselectivity of Triplet Photocycloadditions:1 Diene−Carbonyl Reactions and Solvent Effects
journal contribution
posted on 1998-05-20, 00:00 authored by Axel G. Griesbeck, Stefan Buhr, Maren Fiege, Hans Schmickler, Johann LexThe 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 Paternò−Büchi
reactions of cycloalkenes and cyclic enol ethers.
An increase in steric demand of the α-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 Paternò−Büchi reactions with
2,3-dihydrofuran in polar solvents. Two bicyclic
oxetanes (8 and 10) were characterized by X-ray
structure analysis.