Herein, we report the first example that P(O)-H species including -phosphonates and -phosphine oxides could participate in a highly regioselective 1,4-addition to in situ generated 1-benzopyrylium ion from C3-substituted 2-chromene hemiketals, which provides a brand-new and effective approach for the synthesis of C4-phosphorylated 4-chromenes with diverse C3-functionality (ketone, ester, sulfonyl, aryl, and alkyl groups). In total, the reaction features the use of inexpensive Zn(ClO)·6HO as a catalyst, low catalyst loading (only 5 mol %), mild reaction conditions (60 °C, 10 min to 24 h), and broad substrate scope (46 examples) as well as good to high yields (>90% yield on average). More importantly, mechanistic experiments demonstrated the essential role of the C3-substituent on 2-chromene hemiketals in stabilizing the in situ generated 1-benzopyrylium ion and the regioselective 1,4-addition control.
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