Photoredox-Enabled Dearomative [2π + 2σ] Cycloaddition of Phenols.

Dearomative photocycloaddition of monocyclic arenes is an appealing strategy for comprehending the concept of "escape from flatland". This brings the replacement of readily available planar aromatic hydrocarbon units with a 3D fused bicyclic core with sp3-enriched carbon units. Herein, we outline an intermolecular approach for the dearomative photocycloaddition of phenols. In order to circumvent the ground-state aromaticity and to construct conformationally restrained building blocks, bicyclo[1.1.0]butanes were chosen as coupling partners. This dearomative approach renders straightforward access to a bicyclo[2.1.1]hexane unit fused to a cyclic enone moiety, which further contributed as a synthetic linchpin for postmodifications. Mechanistic experiment advocates for a plausible onset from both the reactants, depending on the redox potential.

ortho-Selective Dearomative [2π + 2σ] Photocycloadditions of Bicyclic Aza-Arenes.

Dearomative photocycloadditions are valuable chemical transformations, serving as an efficient platform to create three-dimensional molecular complexity. However, the photolability of the original addition product especially within the context of ortho cycloadditions often causes undesired consecutive rearrangements, rendering these ortho cycloadducts elusive. Herein, we report an ortho-selective intermolecular photocycloaddition of bicyclic aza-arenes including (iso)quinolines, quinazolines, and quinoxalines by utilizing a strain-release approach. With bicyclo[1.1.0]butanes as coupling partners, this dearomative [2π + 2σ] cycloaddition enables the straightforward construction of C(sp3)-rich bicyclo[2.1.1]hexanes directly connected to N-heteroarenes. Photophysical experiments and DFT calculations revealed the origin of the [2π + 2σ] selectivity and indicate that, in addition to the originally proposed energy transfer or direct excitation pathways, a chain reaction mechanism is operative depending on the reaction conditions.

Cobalt(III)-Catalyzed Enantioselective Intermolecular Carboamination by C-H Functionalization.

High-valent cyclopentadienyl cobalt catalysis is a versatile tool for sustainable C-H bond functionalizations. To harness the full potential of this strategy, control of the stereoselectivity of these processes is necessary. Herein, we report highly enantioselective intermolecular carboaminations of alkenes through C-H activation of N-phenoxyamides catalyzed by CoIII -complexes equipped with chiral cyclopentadienyl (Cpx ) ligands. The method converts widely available acrylates as well as bicyclic olefins into attractive enantioenriched isotyrosine derivatives as well as elaborated amino-substituted bicyclic scaffolds under very mild conditions. The outlined reactivity is unique to the Cpx CoIII complexes and is complementary to the reactivity of 4d- and 5d- precious-metal catalysts.

Sulfonyl Group Dance: A Tool for the Synthesis of 6-Azido-2-sulfonylpurine Derivatives.

9-Substituted 2-chloro-6-sulfonylpurines provide 6-azido-2-sulfonylpurine derivatives with 61-83% yields when treated with sodium azide. Under optimized reaction conditions, the title compounds are obtained in a one-pot process, which involves a sequential treatment of 2,6-dichloropurines with a selected sodium sulfinate and sodium azide. Such a sulfonyl group dance (functional group swap) results from a cascade of SNAr reactions, which are facilitated by azidoazomethine-tetrazole (azide-tetrazole) tautomeric equilibrium. The formation of Meisenheimer-type intermediates as tetrazolopurine tautomers was supported by various spectroscopic methods, including 15N NMR.

Chiral Cyclopentadienyl Cobalt(III) Complexes Enable Highly Enantioselective 3d-Metal-Catalyzed C-H Functionalizations.

The synthesis of a set of cobalt(III)-complexes equipped with trisubstituted chiral cyclopentadienyl ligands is reported, and their steric and electronic parameters are mapped. The application potential of these complexes for asymmetric C-H functionalizations with 3d-metals is shown by the synthesis of dihydroisoquinolones from N-chlorobenzamides with a broad range of alkenes. The transformation proceeds with excellent enantioselectivities of up to 99.5:0.5 er and high regioselectivities. The observed values outperform the best rhodium(III)-based methods for this reaction type. Moreover, challenging substrates such as alkyl alkenes also react with high regio- and enantioselectivities.