General Access to Modified α‐Amino Acids by Bioinspired Stereoselective γ‐C−H Bond Lactonization

C-H Bonds as Functional Groups: Simultaneous Generation of Multiple Stereocenters by Enantioselective Hydroxylation at Unactivated Tertiary C-H Bonds

Enantioselective C-H oxidation is a standing chemical challenge foreseen as a powerful tool to transform readily available organic molecules into precious oxygenated building blocks. Here, we describe a catalytic enantioselective hydroxylation of tertiary C-H bonds in cyclohexane scaffolds with H2O2, an evolved manganese catalyst that provides structural complementary to the substrate similarly to the lock-and-key recognition operating in enzymatic active sites. Theoretical calculations unveil that enantioselectivity is governed by the precise fitting of the substrate scaffold into the catalytic site, through a network of complementary weak non-covalent interactions. Stereoretentive C(sp3)-H hydroxylation results in a single-step generation of multiple stereogenic centers (up to 4) that can be orthogonally manipulated by conventional methods providing rapid access, from a single precursor to a variety of chiral scaffolds.

Chemoselective Oxyfunctionalization of Functionalized Benzylic Compounds with a Manganese Catalyst

Whilst allowing for easy access to synthetically versatile motifs and for modification of bioactive molecules, the chemoselective benzylic oxidation reactions of functionalized alkyl arenes remain challenging. Reported in this study is a new non-heme Mn catalyst stabilized by a bipiperidine-based tetradentate ligand, which enables methylene oxidation of benzylic compounds by H2 O2 , showing high activity and excellent chemoselectivity under mild conditions. The protocol tolerates an unprecedentedly wide range of functional groups, including carboxylic acid and derivatives, ketone, cyano, azide, acetate, sulfonate, alkyne, amino acid, and amine units, thus providing a low-cost, more sustainable and robust pathway for the facile synthesis of ketones, increase of complexity of organic molecules, and late-stage modification of drugs.

Remote Amino Acid Recognition Enables Effective Hydrogen Peroxide Activation at a Manganese Oxidation Catalyst

Precise delivery of a proton plays a key role in O2 activation at iron oxygenases, enabling the crucial O-O cleavage step that generates the oxidizing high-valent metal-oxo species. Such a proton is delivered by acidic residues that may either directly bind the iron center or lie in its second coordination sphere. Herein, a supramolecular strategy for enzyme-like H2 O2 activation at a biologically inspired manganese catalyst, with a nearly stoichiometric amount (1-1.5 equiv) of a carboxylic acid is disclosed. Key for this strategy is the incorporation of an α,ω-amino acid in the second coordination sphere of a chiral catalyst via remote ammonium-crown ether recognition. The properly positioned carboxylic acid function enables effective activation of hydrogen peroxide, leading to catalytic asymmetric epoxidation. Modulation of both amino acid and catalyst structure can tune the efficiency and the enantioselectivity of the reaction, and a study on the oxidative degradation pathway of the system is presented.

Total Synthesis and Late-Stage C-H Oxidations of ent-Trachylobane Natural Products

Herein, we present our studies to construct seven ent-trachylobane diterpenoids by employing a bioinspired two-phase synthetic strategy. The first phase provided enantioselective and scalable access to five ent-trachylobanes, of which methyl ent-trachyloban-19-oate was produced on a 300 mg scale. During the second phase, chemical C-H oxidation methods were employed to enable selective conversion to two naturally occurring higher functionalized ent-trachylobanes. The formation of regioisomeric analogs, which are currently inaccessible via enzymatic methods, reveals the potential as well as limitations of established chemical C-H oxidation protocols for complex molecule synthesis.

Total Synthesis and Late-Stage C-H Oxidations of ent-Trachylobane Natural Products

Herein, we present our studies to construct seven ent-trachylobane diterpenoids by employing a bioinspired two-phase synthetic strategy. The first phase provided enantioselective and scalable access to five ent-trachylobanes, of which methyl ent-trachyloban-19-oate was produced on a 300 mg scale. During the second phase, chemical C-H oxidation methods were employed to enable selective conversion to two naturally occurring higher functionalized ent-trachylobanes. The formation of regioisomeric analogs, which are currently inaccessible via enzymatic methods, reveals the potential as well as limitations of established chemical C-H oxidation protocols for complex molecule synthesis.

Site and Enantioselective Aliphatic C-H Oxidation with Bioinspired Chiral Complexes

Selective oxidation of aliphatic C-H bonds stands as an unsolved problem in organic synthesis, with the potential to offer novel paths for preparing molecules of biological interest. The quest for reagents that can perform this class of reactions finds oxygenases and their mechanisms of action as inspiration motifs. Among the numerous families of synthetic catalysts that have been explored, complexes with linear tetraazadentate ligands combining two aliphatic amines and two aromatic amine heterocycles display a structural versatility proven instrumental in the design of C-H oxidation reactions showing site and enantioselectivities, not accessible by conventional oxidants. This manuscript makes a review of recent advances in the field.