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.