Regioselective Metal-Free Aza-Heck Reactions of Terminal Alkenes Catalyzed by Phosphine Selenides

Asymmetric Migratory Tsuji-Wacker Oxidation Enables the Enantioselective Synthesis of Hetero- and Isosteric Diarylmethanes

Diarylmethanes play, in part, a pivotal role in the design of highly potent, chiral, nonracemic drugs whose bioactivity is typically affected by the substitution pattern of their arene units. In this context, certain arenes such as para-substituted benzenes or unsubstituted heteroarenes cause particular synthetic challenges, since such isosteric residues at the central methane carbon atom are typically indistinguishable for a chiral catalyst. Hence, the stereoselective incorporation of isosteric (hetero)arenes into chiral methane scaffolds requires the use of stoichiometrically differentiated building blocks, which is typically realized through preceding redox-modifying operations such as metalation or halogenation and thus associated with disadvantageous step- and redox-economic traits. As a counter-design, we report herein a generalized enantioselective synthesis of chiral diarylmethanes by means of an asymmetric migratory Tsuji-Wacker oxidation of simple stilbenes. The title protocol relies on the well-adjusted interplay of aerobic photoredox and selenium-π-acid catalysis to allow for the installation of a broad variety of arenes, including isosteric ones, into the methane core. Facial differentiation and regioselectivity are solely controlled by the selenium catalyst, which (a) renders the E/Z-configuration of the stilbene substrates inconsequential and (b) permits the stereodivergent synthesis of both product enantiomers from a single catalyst enantiomer, simply by employing constitutionally isomeric starting materials. Altogether, this multicatalytic platform offers the target structures with high levels of enantioselectivity in up to 97% ee, which has also been successfully exploited in expedited syntheses of antihistaminic (R)- and (S)-neobenodine.

Intermolecular Aza-Wacker Coupling of Alkenes with Azoles by Photo-Aerobic Selenium-π-Acid Multicatalysis

Herein, the intermolecular, photoaerobic aza-Wacker coupling of azoles with alkenes by means of dual and ternary selenium-π-acid multicatalysis is presented. The title method permits an expedited avenue toward a broad scope of N-allylated azoles and representative azinones under mild conditions with broad functional group tolerance, as is showcased in more than 60 examples including late-stage drug derivatizations. From a regiochemical perspective, the protocol is complementary to cognate photoredox catalytic olefin aminations, as they typically proceed through either allylic hydrogen atom abstraction or single electron oxidation of the alkene substrate. These methods predominantly result in C-N bond formations at the allylic periphery of the alkene or the less substituted position of the former π-bond (i.e., anti-Markovnikov selectivity). The current process, however, operates through a radical-polar crossover mechanism, which solely affects the selenium catalyst, thus allowing the alkene to be converted strictly through an ionic two-electron transfer regime under Markovnikov control. In addition, it is shown that the corresponding N-vinyl azoles can also be accessed by sequential or one-pot treatment of the allylic azoles with base, thus emphasizing the exquisite utility of this method.

Selective Hydrofunctionalization of N-Allenyl Derivatives with Heteronucleophiles Catalyzed by Brønsted Acids

In this study, we present a novel and environmentally sustainable protocol for the γ-hydrofunctionalization of N-allenyl compounds using various heteronucleophiles catalyzed solely by simple Brønsted acids. The method displays remarkable attributes, highlighting its sustainability, efficiency, regio- and stereoselectivity, as well as its versatile applicability to diverse heteroatom-containing enamides. Notably, our approach eliminates the need for metal catalysts and toxic solvents, representing a significant advancement in greener chemistry practices. We demonstrate the broad scope of our protocol by successfully scaling up reactions to gram-scale syntheses, underscoring its robustness for potential industrial implementation. The resulting γ-heterosubstituted enamides offer new possibilities for further synthetic transformations, yielding highly functionalized compounds with diverse applications. Mechanistic investigations reveal the pivotal role of CSA as a catalyst, enabling alcohol addition via a covalent activation mode.

Palladium-Catalyzed E-Selective Oxidative Amination of Aromatic Amine with 3-Butenoic Acid

A palladium-catalyzed oxidative amination of inactive olefins with an aromatic amine was developed using a copper acetate oxidant to yield corresponding secondary and tertiary enamines in moderate to good yields. This new procedure outlines an efficient approach for the construction of enamine skeletons.

Catalytic Metal-free Allylic C-H Amination of Terpenoids

The selective replacement of C-H bonds in complex molecules, especially natural products like terpenoids, is a highly efficient way to introduce new functionality and/or couple fragments. Here, we report the development of a new metal-free allylic amination of alkenes that allows the introduction of a wide range of nitrogen functionality at the allylic position of alkenes with unique regioselectivity and no allylic transposition. This reaction employs catalytic amounts of selenium in the form of phosphine selenides or selenoureas. Simple sulfonamides and sulfamates can be used directly in the reaction without the need to prepare isolated nitrenoid precursors. We demonstrate the utility of this transformation by aminating a large set of terpenoids in high yield and regioselectivity.

Selenophosphoramide-catalyzed diamination and oxyamination of alkenes

Scavenging fluoride from a selenophosphoramide-catalyzed alkene oxidation reaction suppresses the known syn-elimination pathway, enabling alkene diamination/oxyamination reactions via substitution.

A new selenophosphoramide-catalyzed diamination of terminal- and trans-1,2-disubstituted olefins is presented. Key to the success of this transformation was the introduction of a fluoride scavenger, trimethylsilyl trifluoromethanesulfonate (TMSOTf), to prevent a competitive syn-elimination pathway, as was the use of a phosphoramide ligand on selenium to promote the desired substitution reaction. A screen of catalysts revealed that more electron-rich phosphine ligands resulted in higher yields of the desired product, with selenophosphoramides giving the optimal results. A broad range of substrates and functional groups were tolerated and yields were generally good to excellent. For (E)-1,2-disubstituted olefins, diastereoselectivities were always high, giving exclusively anti products. The conditions were also applied to substrates bearing internal nucleophiles such as esters and carbonates, giving rise to 1,2-aminoesters and cyclic carbonates, respectively.