An efficient method is reported for the preparation of multicyclic pyridines and quinolines by a rhodium-catalyzed intramolecular C−H bond functionalization process. The method shows good scope for branched and unbranched alkyl substituents on the pyridine ring and at the R position of the tethered alkene group. Starting materials capable of undergoing olefin isomerization to provide terminal 1,1-disubstituted alkenes also proved to be effective substrates.

The concise total synthesis of (−)-aurantioclavine has been achieved by taking advantage of strategies for the asymmetric alkenylation of N-tert-butanesulfinyl imines. The enantiomerically pure natural product was prepared in 6 steps and 27% overall yield by using Rh-catalyzed addition of a N-methyliminodiacetic acid (MIDA) boronate and in 5 steps and 29% yield by employing a Grignard reagent addition sequence.

The enantioselective intramolecular alkylation of substituted imidazoles with enantiomeric excesses up to 98% has been accomplished by rhodium catalyzed C–H bond functionalization with (S,S′,R,R′)TangPhos as the chiral ligand.

An efficient 1,2-deoxygenation method, involving an unexpected mechanism, was found for simple diols and for biomass-derived polyols (glycerol and erythritol) that results in the conversion of the 1,2-dihydroxy group to a carbon–carbon double bond.

A method for the direct arylation of benzotriazepines is reported, employing an aryl iodide as the coupling partner, copper iodide as the catalyst, and lithium tert-butoxide as the base. A variety of electron-rich, electron-poor, and sterically hindered aryl iodides are compatible with the reaction conditions. The arylation reaction can also be performed outside a glovebox in air without a significant decrease in yield. Furthermore, convenient microwave conditions for carrying out this transformation are reported.

The one-pot preparation of N-sulfinylamine diastereomers proceeds in excellent yields (84−98%) for a diverse set of N-sulfinyl imine addition products. The method is operationally simple and extractive isolation provides analytically pure mixtures of diastereomers as standards for the rapid and accurate determination of N-sulfinylamine diastereomeric purity.

Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct functionalization of nitrogen heterocycles through C−H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes our work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. We initially discovered an intramolecular Rh-catalyzed C-2 alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. We then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, we discovered that a novel substrate-derived Rh−N-heterocyclic carbene (NHC) complex was involved as an intermediate. We then synthesized analogous Rh−NHC complexes directly by treating precursors to the intermediate [RhCl(PCy3)2] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazoline, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy3)2 fragment coordinates to the heterocycle before intramolecular activation of the C−H bond occurs. The resulting Rh−H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid cocatalysts accelerate the alkylation, we developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. We demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, we developed conditions to directly arylate these heterocycles with aryl halides. Our initial conditions that used PCy3 as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (phoban) that also facilitated the coupling of aryl bromides. We then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, we anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C−H bond functionalization reactions, resulting in the design of more efficient and robust catalysts, expanded substrate scope, and new transformations.

An efficient 1,2-deoxygenation method, involving an unexpected mechanism, was found for simple diols and for biomass-derived polyols (glycerol and erythritol) that results in the conversion of the 1,2-dihydroxy group to a carbon–carbon double bond.

The enantioselective intramolecular alkylation of substituted imidazoles with enantiomeric excesses up to 98% has been accomplished by rhodium catalyzed C–H bond functionalization with (S,S′,R,R′)TangPhos as the chiral ligand.