We have shown here that weak interactions such as halogen bonding (XB) can be used to activate the carbonyl group of α,β-unsaturated ketones. Carbon tetrabromide (CBr) has been used as the sole reagent for the selective synthesis of flavanones and aza-flavanones from the corresponding 2'-hydroxy- and 2'-aminochalcones under metal-free and additive-free conditions. DFT calculations support the catalytic role of XB between the oxygen of chalcones and CBr in these reactions.
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