Hypervalent Activation as Key Step for Dehydrogenative ortho C-C Coupling of Iodoarenes

Abstract

<p> Building on earlier results, a direct metal-free &alpha;- arylation of substituted cyclic 1,3-diones using ArI(O_{<font size="2">2</font>}CCF_{<font size="2">3</font>})_{<font size="2">2</font>} reagents has been developed; unlike other arylative approaches, the arylated products retain the iodine substituent <em>ortho</em> to the newly formed C-C bond. The mechanism is explored by using DFT calculations, which show a vanishingly small activation barrier for the C-C bond-forming step. In fact, taking advantage of an efficient in situ hypervalent activation, the iodoarenes are shown to undergo a cross- dehydrogenative C-C coupling at the C-H <em>ortho</em> to the iodine. When Oxone is used as terminal oxidant, the process is found to benefit from a rapid initial formation of the hypervalent ArI(OR)_{<font size="2">2</font>} species and the sulfate-accelerated final coupling with a ketone. This method complements the <em>ipso</em> selectivity obtained in the metal-catalyzed &alpha;-arylation of carbonyl compounds.</p>