Cytochrome P450 enzymes have been engineered to catalyze abiological C-H bond amination reactions, but the yields of these reactions have been limited by low chemoselectivity for the amination of C-H bonds over competing reduction of the azide substrate to a sulfonamide. Here we report that P450s derived from a thermophilic organism and containing an iridium porphyrin cofactor (Ir(Me)-PIX) in place of the heme catalyze enantioselective intramolecular C-H bond amination reactions of sulfonyl azides. These reactions occur with chemoselectivity for insertion of the nitrene units into C-H bonds over reduction of the azides to the sulfonamides that is higher and with substrate scope that is broader than those of enzymes containing iron porphyrins. The products from C-H amination are formed in up to 98% yield and ∼300 TON. In one case, the enantiomeric excess reaches 95:5 er, and the reactions can occur with divergent site selectivity. The chemoselectivity for C-H bond amination is greater than 20:1 in all cases. Variants of the Ir(Me)-PIX CYP119 displaying these properties were identified rapidly by evaluating CYP119 mutants containing Ir(Me)-PIX in cell lysates, rather than as purified enzymes. This study sets the stage to discover suitable enzymes to catalyze challenging C-H amination reactions.

The diverse biological activities of tocopherols and their analogs have inspired considerable interest in the development of routes for their efficient asymmetric synthesis. Here, we report that chiral ammonium hypoiodite salts catalyze highly chemo- and enantioselective oxidative cyclization of γ-(2-hydroxyphenyl)ketones to 2-acyl chromans bearing a quaternary stereocenter, which serve as productive synthetic intermediates for tocopherols. Raman spectroscopic analysis of a solution of tetrabutylammonium iodide and tert-butyl hydroperoxide revealed the in situ generation of the hypoiodite salt as an unstable catalytic active species and triiodide salt as a stable inert species. A high-performance catalytic oxidation system (turnover number of ~200) has been achieved through reversible equilibration between hypoiodite and triiodide in the presence of potassium carbonate base. We anticipate that these findings will open further prospects for the development of high-turnover redox organocatalysis.

C–H bonds are ubiquitous and abundant in organic molecules. If C–H bonds could be directly converted to desired functional groups in a chemo‐, site‐, and stereoselective manner, C–H functionalization would be a strong and useful tool for organic synthesis. Recent developments in catalytic and enzymatic chemistry have achieved highly sustainable and selective nitrene C–H insertion. Initially, C–H amination was inspired by model studies on enzymatic oxidation and used iminoiodinanes, nitrogen analogs of iodosobenzene, as nitrene precursors. Transition‐metal/iminoiodinane systems are well studied and established. These systems can directly introduce sulfonamide groups with excellent stereoselectivity, albeit with co‐production of iodobenzene as waste material. Fortunately, the atom economics of this methodology were improved by introducing highly sustainable nitrene sources such as azide compounds and 1,2,4‐dioxazol‐5‐one derivatives. In this review, we present the details of these developments with respect to their catalysts and nitrene sources.

The dearomative dicarboxylation of stable heteroaromatics using CO 2 is highly challenging but represents a very powerful method for producing synthetically useful dicarboxylic acids, which can potentially be employed as intermediates of biologically active molecules such as natural products and drug leads. However, these types of transformations are still underdeveloped, and concise methodologies with high efficiency (e.g., high yield and high selectivity for dicarboxylations) have not been reported. We herein describe a new electrochemical protocol using the CO 2 radical anion (E 1/2 of CO 2 = −2.2 V in DMF and −2.3 V in CH 3 CN vs SCE) that produces unprecedented trans-oriented 2,3-dicarboxylic acids from N-Ac-, Boc-, and Ph-protected indoles that exhibit highly negative reduction potentials (−2.50 to −2.94 V). On the basis of the calculated reduction potentials, Nprotected indoles with reduction potentials up to −3 V smoothly undergo the desired dicarboxylation. Other heteroaromatics, including benzofuran, benzothiophene, electron-deficient furans, thiophenes, 1,3-diphenylisobenzofuran, and N-Boc-pyrazole, also exhibit reduction potentials more positive than −3 V and served as effective substrates for such dicarboxylations. The dicarboxylated products thus obtained can be derivatized into useful synthetic intermediates for biologically active compounds in few steps. We also show how the dearomative monocarboxylation can be achieved selectively by choice of the electrolyte, solvent, and protic additive; this strategy was then applied to the synthesis of an octahydroindole-2-carboxylic acid (Oic) derivative, which is a useful proline analogue.