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1. Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage

   https://doi.org/10.1055/s-0040-1707101  

   Li, Guangchen; Szostak, Michal (January 2020, Synthesis)

   In the past several years, tremendous advances have been made in non-classical routes for amide bond formation that involve transamidation and amidation reactions of activated amides and esters. These new methods enable the formation of extremely valuable amide bonds via transition-metal- catalyzed, transition-metal-free or metal-free pathways by exploiting chemoselective acyl C–X (X = N, O) cleavage under mild conditions. In a broadest sense, these reactions overcome the formidable challenge of activating C–N/C–O bonds of amides or esters by rationally tackling nN→π*C=O delocalization in amides and nO→π*C=O donation in esters. In this account, we summarize the recent remarkable advances in the development of new methods for the synthesis of amides with a focus on (1) transition-metal/NHC- catalyzed C–N/C–O bond activation, (2) transition-metal-free highly selective cleavage of C–N/C–O bonds, (3) the development of new acyl-transfer reagents, and (4) other emerging methods. 

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2. Reaction of Carboxylic Acids and Dehydroalanine Allyl Esters via One‐Pot Sequential Decarboxylative Couplings

   https://doi.org/10.1002/cctc.202500696  

   Londhe, Shrikant_S; Waller, Colin_W; Tunge, Jon_A (June 2025, ChemCatChem)

   Abstract A protocol for the iterative decarboxylative cross‐coupling of carboxylic acids with dehydroalanine (Dha) allyl esters is described. A procedure for decarboxylative Giese addition to dehydroalanine allyl esters that avoids 5‐exo‐trig radical cyclization onto the allyl moiety was developed. This results in complex, substituted alanine allyl esters that are poised for a second decarboxylative coupling. Thus, following the photocatalytic decarboxylative alkylation of Dha, the resulting amino acid allyl esters were subjected to decarboxylative allylation under metallaphotoredox/palladium catalysis. The Giese addition and decarboxylative allylation can be performed in one pot simply by triggering the decarboxylative allylation by addition of a palladium catalyst. These one‐pot decarboxylative couplings leverage temporally controlled carboxylate formation to allow controlled, sequential photoredox activation of the carboxylates. The ability to perform sequential, one‐pot photoredox C─C bond formations obviates the need for isolation of intermediates. The final products of these coupling reactions are densely functionalized homoallylic amines and/or unsymmetric, differentiated 1,3‐diamines, both known for their high synthetic value. 

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3. Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes

   https://doi.org/10.1021/jacs.3c00181  

   Parsutkar, Mahesh M.; Bhunia, Subhajit; Majumder, Mayukh; Lalisse, Remy F.; Hadad, Christopher M.; RajanBabu, T.V. (April 2023, Journal of the American Chemical Society)

   ABSTRACT: Enantiopure homoallylic boronate esters are versatile intermediates because the C–B bond in these com-pounds can be stereospecifically transformed into C–C, C–O and C–N bonds. Regio- and enantioselective synthesis of these precursors from 1,3-dienes has few precedents in the literature. We have identified reaction conditions and ligands for the synthesis of nearly enantiopure (er >97:3 to >99:1) homoallylic boronate esters via a rarely seen cobalt-catalyzed [4,3]-hydroboration of 1,3-dienes. Monosubstituted or 2,4-disubstituted linear dienes undergo highly efficient, regio- and enanti-oselective hydroboration with HBPin catalyzed by [(L*)Co]+[BARF]–, where L* is typically a chiral bis-phosphine ligand with a narrow bite angle. Several such ligands (examples: i-PrDuPhos, QuinoxP*, Duanphos and, BenzP*) that give high enantioselectivities for the [4,3]-hydroboration product have been identified. In addition, the equally challenging problem of regioselectivity is uniquely solved with a dibenzooxaphosphole ligand, (R,R)-MeO-BIBOP. A cationic cobalt(I) complex of this ligand is a very efficient (TON >960) catalyst, while providing excellent regioselectivities (rr >98:2) and enantioselectiv-ities (er >98:2) for a broad range of substrates. A detailed computational investigation of the reactions using Co-complexes from two widely different ligands (BenzP* and MeO-BIBOP) employing B3LYP-D3 density functional theory provides key insights into the mechanism and the origins of selectivities. The computational results are in full agreement with the exper-iments. For the complexes we have examined thus far, the relative stabilities of the diastereomeric diene-bound complexes [(L*)Co(4-diene)]+ leads to the initial diastereofacial selectivity, which in turn is retained in the subsequent steps, providing exceptional enantioselectivity for the reactions. 

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4. Synthesis of Amides by Transamidation and Amidation of Activated Amides and Esters

   Li, Guangchen; Szostak, Michal (January 2020, Science of synthesis)

   This chapter provides a summary of the recent advances in direct transamidation and amidation reactions of activated amides and esters via transition- metal-catalyzed and transition-metal-free C(acyl)–N and C(acyl)–O bond cleavage as a new disconnection for the synthesis of amide bonds. 

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5. Functionalized vinyldiazo compounds: New players in asymmetric catalysis

   https://doi.org/10.1016/j.checat.2023.100770  

   Bao, M; De_Angeles, L; Rada, MS; Baird, M; Arman, H; Wherritt, D; Doyle, MP (October 2023, Chem Catalysis)

   The catalytic uses of metal carbenes for addition, insertion, and cycloaddition reactions are dependent on their carbene precursor. The limited methods available for the preparation of diazo esters, which are the most common carbene precursors, restricts their ability to impart structural diversity in metal carbene reactions. Here we report a new methodology for the preparation of diverse vinyldiazoacetate esters and their effective uses in highly enantiocontrolled cyclopropanation, N-H bond insertion, O-H bond insertion, and [3+2] cycloaddition reactions. 1,2,3-Triazine 1-oxides with a sp3-C-H bond at the 5-position undergo base catalyzed Dimroth-type rearrangement to form multiply substituted oximidovinyldiazoacetates in high yields at or below room temperature, and these diverse vinyldiazo compounds undergo catalytic metal carbene transformations to produce oximidovinylcyclopropanes, α-oximidovinyl-α-amino acids and α-hydroxy acids, as well as tricyclic indole derivatives in high yields and enantioselectivities. The new access to vinyldiazo compounds has applicability to a vast array of metal carbene transformations. 

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