Kupferkatalysierte C-C-Kupplung von Thiolestern und Boronsäuren unter aeroben Bedingungen

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

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 Liebeskind-Srogl C-C cross-coupling reaction

Although a plethora of highly selective and reliable methods for the construction of C-C bonds are known to organic chemists, there is growing interest in the development of new protocols that offer different or orthogonal reactivity to that of existing methods. In 2000, Liebeskind and Srogl described a mechanistically unprecedented transition-metal-catalyzed cross-coupling of thioesters with boronic acids to produce ketones under neutral conditions. This desulfitative cross-coupling process is catalytic in palladium(0), stoichiometric in copper(I), and applicable to a range of organosulfur derivatives and nucleophilic organometallic reagents. In this Minireview, we highlight recent applications of this intriguing cross-coupling reaction in modern organic synthesis, with an emphasis on cases in which traditional methods for C-C bond formation have failed.