The Vinyl Moiety as a Handle for Regiocontrol in the Preparation of Unsymmetrical 2,3-Aliphatic-Substituted Indoles and Pyrroles

Investigation and comparison of the mechanistic steps in the [(Cp*MCl2)2] (Cp* = C5Me5; M = Rh, Ir)-catalyzed oxidative annulation of isoquinolones with alkynes

The mechanism of the [(Cp*MCl(2))(2)] (M = Rh, Ir)-catalyzed oxidative annulation reaction of isoquinolones with alkynes was investigated in detail. In the first acetate-assisted C-H-activation process (cyclometalated step) and the subsequent mono-alkyne insertion into the M-C bonds of the cyclometalated compounds, both Rh and Ir complexes participated well. However, the desired final products, dibenzo[a,g]quinolizin-8-one derivatives, were only formed in high yield when the Rh species participated in the final oxidative coupling of the C-N bond. Moreover, a Rh(I) sandwich intermediate was isolated during this transformation. The iridium complexes were found to be inactive in the oxidative coupling processes. All of the relevant intermediates were fully characterized and determined by single-crystal X-ray diffraction analysis. Based on this mechanistic study, a Rh(III)→Rh(I)→Rh(III) catalytic cycle was proposed for this reaction.

Access to sultams by rhodium(III)-catalyzed directed C-H activation

Director's cut: The pharmaceutically relevant sulfonamide group is shown to be a competent directing group for [Cp*Rh(OAc)(2)]-catalyzed C-H functionalizations. Reactions of the cyclometalated intermediate with internal alkynes provide access to a wide range of sultam derivatives. The reaction is high yielding and works best under aerobic conditions with catalytic amounts of CuOAc as an oxidation mediator. Cp* = C(5)Me(5).

Facile preparation of indoles and 1,2-benzothiazine 1,1-dioxides: nucleophilic addition of sulfonamides to bromoacetylenes and subsequent palladium-catalyzed cyclization

Bromine as a double agent: The bromine atom in 1-bromo-1-alkynes works as an electron-withdrawing group to effect the nucleophilic addition of sulfonamides. It again plays a pivotal role in the palladium-catalyzed cyclization of the resultant (Z)-2-(sulfonylamino)-1-bromoalkenes into nitrogen heterocycles (see scheme).

Mild rhodium(III)-catalyzed C-H activation and intermolecular annulation with allenes

All(enes) great! A novel Rh(III)-catalyzed oxidative coupling with allenes under mild conditions provides heterocycles with exocyclic double bonds. This reaction features low catalyst loadings, high regio- and stereoselectivity, and excellent substrate scope. The products were derivatized and preliminary mechanistic studies were conducted.

Amide-directed tandem C-C/C-N bond formation through C-H activation

The transformation of C-H bonds into other chemical bonds is of great significance in synthetic chemistry. C-H bond-activation processes provide a straightforward and atom-economic strategy for the construction of complex structures; as such, they have attracted widespread interest over the past decade. As a prevalent directing group in the field of C-H activation, the amide group not only offers excellent regiodirecting ability, but is also a potential C-N bond precursor. As a consequence, a variety of nitrogen-containing heterocycles have been obtained by using these reactions. This Focus Review addresses the recent research into the amide-directed tandem C-C/C-N bond-formation process through C-H activation. The large body of research in this field over the past three years has established it as one of the most-important topics in organic chemistry.