Straightforward Access to Pentafluorosulfanylated Phenols and Aminophenols via [4 + 2] Diels-Alder Cycloaddition...

Here is described a theoretical and experimental study of regioselective [4 + 2] Diels-Alder cycloaddition reactions between electron-rich dienes and SF₅-alkynes. These methods give straightforward and convergent access to SF₅-phenols and aminophenols in short reaction sequences. Density functional theory (DFT) calculations combined with reactivity tools, activation strain model, and energy decomposition analysis provide a deeper mechanistic understanding of these Diels-Alder cycloaddition reactions involving an alkyne as a dienophile. We found that regioselectivity and reactivity originate from less destabilizing strain energy and reduced Pauli repulsion between occupied π-orbitals of the diene and dienophile, rather than from stabilizing highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) interactions. This can be ascribed to a higher degree of asynchronicity in the transition state of the privileged attack of the diene on the dienophile.