Transient and Recyclable Halogenation Coupling (TRHC) for Isoflavonoid Synthesis with Site‐Selective Arylation

A transient and recyclable C−H iodination has been designed for the synthesis of isoflavonoids through the domino reactions of o ‐hydroxyphenyl enaminones and aryl boronic acids in the presence of catalytic KI and Pd catalyst. Instead of the conventional cross‐coupling strategy employing pre‐halogenated substrates, this method transforms raw C−H bond by means of a transient C−H halogenation to smoothly relay the subsequent C‐arylation. Consequently, such a method avoids the pre‐functionalization for C−halogen bond installation as well as the generation of stoichiometric halogen‐containing waste following the cross‐coupled product, disclosing an intriguing new coupling protocol to forge the C−C bond in the virgin area between classical C−X (X=halogen) bond cross coupling and the C−H activation.