Sigmatropic Rearrangements of Hypervalent‐Iodine‐Tethered Intermediates for the Synthesis of Biaryls

Abstract

Metal-free dehydrogenative couplings of aryliodanes with phenols to afford 2-hydroxy-2'-iodobiaryls have been developed. This reaction proceeds through ligand exchange on the hypervalent iodine atom followed by a [3,3] sigmatropic rearrangement and with complete regioselectivity. This coupling, in combination with in situ oxidation by mCPBA, enables the convenient conversion of iodoarenes into desirable biaryls. The obtained biaryls have convertible iodo and hydroxy groups in close proximity, and are thus synthetically useful, as exemplified by the controlled syntheses of π-extended furans and a substituted [5]helicene. DFT calculations clearly revealed that the rearrangement is sigmatropic, with C-C bond formation and I-O bond cleavage proceeding in a concerted manner. Acetic acid, which was found to be the best solvent for this protocol, renders the iodine atom more cationic and thus accelerates the sigmatropic rearrangement.

The Coming of Age in Iodane‐Guided ortho‐C−H Propargylation: From Insight to Synthetic Potential

“…While previous DFT calculations confirmed the viability of an iodine‐containing cyclic transition state,, these studies did not extend to the original propargylation reaction. In this context, two very intriguing aspects of this reaction manifold have remained unaddressed, the first of which is the exact nature of both the transition state and of the initially formed cationic rearranged species.…”

Dearomative Dual Functionalization of Aryl Iodanes

“…To verify our hypothesis, we first needed to identify the first nucleophile (Nu 1 ) to be used for [3,3] sigmatropic rearrangement of the aryl iodane (Scheme e). A variety of nucleophiles, including allyl/propargyl silanes,– β‐dicarbonyl compounds, 2‐naphthols, difluoroenol silyl ethers, and α‐stannyl nitriles, were found to be suitable for the rearrangement of aryl iodanes. However, the selection of nucleophiles for dearomative rearrangement must meet the following criteria: 1) The rearrangement of aryl iodanes with the nucleophile must take place at low temperature and be complete in a short time so as to avoid the deterioration of the in situ generated dearomative intermediate I , which is likely to be unstable in view of its dearomatized structure with a pendant iodine(III) moiety; 2) the nucleophile must be highly reactive towards aryl iodanes in the rearrangement stage, but completely inactive towards the highly electrophilic dearomative intermediate I so that I can be trapped by the second nucleophile (Nu 2 ; Scheme e); 3) the nucleophile should be a versatile building block to ensure the synthetic utility of the final dearomatization product.…”

Synthesis of Polysubstituted Iodoarenes Enabled by Iterative Iodine‐Directed para and ortho C−H Functionalization

“…The exclusive ortho selectivity has been rationalized via a [3,3]‐sigmatropic rearrangement of allenyl iodonium intermediate I (Scheme A). The concept was recently expanded to additional manifolds, including C−H allylation as well as C−H coupling with enols (via enolate II ), and naphthols (Scheme B–D). Related sulfoxide‐directed coupling reactions have also been developed, particularly through contributions from the groups of Procter, Maulide, and Yorimitsu .…”