Regio- and Stereoselectivity in the Paternò-Büchi Reaction Between 2,3-Dihydrofuran and Furan with Benzaldehyde

The photochemical coupling reaction between 2,3-dihydrofuran and benzaldehyde was studied byusing DFT/B3LYP/6-31G+(d,p) method. The regiochemistry of the attack of the benzaldehyde on the double bond is related to the different stability of the biradical intermediates. The endo stereoselectivity of theproduct depends on the superposition between HSOMO and LSOMO in the biradical intermediate. The photochemical reaction between furan and benzaldehyde was studied at the same level. The regioselectivity depends on the relative stability of the possible biradical intermediates. The exo stereoselectivity of the coupling product depends on the superposition between the HSOMO and LSOMO of the biradical intermediate.