A DFT study of 1,4-biradical intermediates involved in stereoselective Paternò-Buechi reactions

The stereoselectivity of the reaction of silyl enol ethers with benzaldehyde is explained by using DFT calculations, considering the relative stability of the possible stereoisomers of the biradical intermediates and the coupling between the single occupied molecular orbitals (SOMOs) of those intermediates. The same approach can be used to justify the observed endo stereoselectivity in the reaction of 2,3-dihydrofuran with 2,4,6-trimethylbenzaldehyde and the exo stereoselectivity in the reaction of the same substrate with 2-naphthaldehyde