Enantioselective photoenolization/Diels-Alder reaction catalyzed by chiral Brønsted acid

Photoenolization/Diels-Alder (PEDA) reaction has emerged as a promising strategy for constructing benzannulated carbocyclic frameworks in modern synthetic chemistry. However, the high reactivity of photoinduced intermediates typically necessitates a substoichiometric amount of chiral catalyst for sufficient enantiocontrol, thereby limiting the development of catalytic asymmetric PEDA reaction. Herein, we report a chiral Brønsted acid-catalyzed asymmetric PEDA reaction under mild conditions, which achieves highly enantioselective [4+2] cycloaddition of aryl ketones with vinylazaarenes by stabilizing transient photoenol intermediates. This strategy enables straightforward access to azaarene-containing chiral carbocyclic adducts and attractive enantioenriched spiro lactones in good yields with excellent enantioselectivity (up to 97% yield, >19:1 dr, >99% ee). Notably, control experiments and mechanism studies indicate that unique multifunctional activation of chiral Brønsted acids is crucial for achieving high reactivity and enantiocontrol.