Cobalt(II) Porphyrin Catalyzed Cascade Reaction of Pyrrolyl Ketones for Construction of Polysubstituted Pyrrolizidines and Pyrrolizines

A Convergent, Modular Approach to Trifluoromethyl-Bearing 5-Membered Rings via Catalytic C(sp3 )-H Activation

Trifluoromethyl-bearing 5-membered rings are prevalent in bioactive molecules, but modular approaches to these compounds by functionalization of robust C(sp³ )-H bonds in a direct and selective manner are extremely challenging. Herein we report the rhodium-catalyzed α-CF₃ -α-alkyl carbene insertion into C(sp³ )-H bonds of a broad range of substrates to access 7 types of CF₃ -bearing saturated 5-membered carbo- and heterocycles. The reaction is particularly effective for benzylic C-H insertion exerting good site-, diastereo- and enantiocontrol, and applicable to the synthesis of chiral CF₃ analogues of bioactive molecules. Ruthenium α-CF₃ -α-alkyl carbene complexes underwent stoichiometric reactions to give C-H insertion products, lending evidence for the involvement of metal α-CF₃ -α-alkyl carbene species in the catalytic cycle. DFT calculations revealed that the π⋅⋅⋅π attraction and intra-carbene C-H⋅⋅⋅F hydrogen bond elucidate the origin of selectivity of the benzylic C-H insertion reactions.

Catalytic, Asymmetric Dearomative Synthesis of Complex Cyclohexanes via a Highly Regio- and Stereoselective Arene Cyclopropanation Using α-Cyanodiazoacetates

Arene cyclopropanation offers a direct route to higher-order, non-aromatic carbocycles; however, the inherent issue of dictating site selectivity has cumbered the development of novel intermolecular reactions that directly engage the arene pool. This paper describes a highly regio- and stereoselective, Rh₂[(S)-PTTL]₄-catalyzed arene cyclopropanation using α-cyanodiazoacetates to afford stable norcaradienes bearing three stereogenic centers, one of which is an all-carbon quaternary center. The enantioenriched norcaradienes served as tunable templates for further transformation into stereochemically dense, fused and bicyclic carbocycles containing transmutable functionality.

Stable group 8 metal porphyrin mono- and bis(dialkylcarbene) complexes: synthesis, characterization, and catalytic activity

Alkyl-substituted carbene (CHR or CR2, R = alkyl) complexes have been extensively studied for alkylcarbene (CHR) ligands coordinated with high-valent early transition metal ions (a.k.a. Schrock carbenes or alkylidenes), yet dialkylcarbene (CR2) complexes remain less developed with bis(dialkylcarbene) species being little (if at all) explored. Herein, several group 8 metal porphyrin dialkylcarbene complexes, including Fe- and Ru-mono(dialkylcarbene) complexes [M(Por)(Ad)] (1a,b, M = Fe, Por = porphyrinato dianion, Ad = 2-adamantylidene; 2a,b, M = Ru) and Os-bis(dialkylcarbene) complexes [Os(Por)(Ad)2] (3a-c), are synthesized and crystallographically characterized. Detailed investigations into their electronic structures reveal that these complexes are formally low-valent M(ii)-carbene in nature. These complexes display remarkable thermal stability and chemical inertness, which are rationalized by a synergistic effect of strong metal-carbene covalency, hyperconjugation, and a rigid diamondoid carbene skeleton. Various spectroscopic techniques and DFT calculations suggest that the dialkylcarbene Ad ligand is unique compared to other common carbene ligands as it acts as both a potent σ-donor and π-acceptor; its unique electronic and structural features, together with the steric effect of the porphyrin macrocycle, make its Fe porphyrin complex 1a an active and robust catalyst for intermolecular diarylcarbene transfer reactions including cyclopropanation (up to 90% yield) and X-H (X = S, N, O, C) insertion (up to 99% yield) reactions.

Iron- and cobalt-catalyzed C(sp3)–H bond functionalization reactions and their application in organic synthesis

This review highlights the developments in iron and cobalt catalyzed C(sp³)–H bond functionalization reactions with emphasis on their applications in organic synthesis, i.e. natural products and pharmaceuticals synthesis and/or modification.

An Efficient Synthesis of Aryl-Substituted Pyrroles by the Suzuki⁻Miyaura Coupling Reaction of SEM-Protected Pyrroles

An efficient arylation of SEM-protected pyrroles by the Suzuki-Miyaura coupling reaction has been developed. The reaction can be carried out under mild conditions to provide aryl-substituted pyrroles in moderate to excellent yields. The scope and limitations of the methodology were evaluated, and the reaction was tolerant of a wide range of functionalities. Compared to the reported methods, the protocol has some advantages, such as commercially available materials, no debrominated by-products being formed, and the amine-protecting group being stable under the reaction conditions. The synthetic utility of the product has also been demonstrated, with several common transformations of the aryl-substituted pyrrole product being conducted. This protocol will offer the opportunity to explore other metal-catalyzed cross-coupling reactions employing SEM-protected pyrroles.