Regiodivergent Synthesis Utilizing Alkyl Hex-5-en-2-ynoates and 3-Homoacyl Coumarins: Phenol-Mediated Controllable Phosphine-Catalyzed Michael and 1,7-Umpolung Addition

We disclose a first example of regiodivergent addition between alkyl hex-5-en-2-ynoates and 3-homoacyl coumarins under phosphine catalysis, in which phenol serves as a decisive additive. This study demonstrates a phenol-mediated switchable pathway between Michael addition and 1,7-umpolung addition, expanding the scope of alkynoate reactivity with biologically relevant pronucleophiles. The reaction proceeds under mild conditions with high regioselectivity, broad substrate scope, and good functional group tolerance, and its utility was validated through scale-up and product derivatization. Mechanistic studies reveal that solvent-modulated phenol acidity directs regioselectivity and drives the control of kinetic Michael adducts and thermodynamically favored 1,7-adducts.