Reactions of a Carbamoylstannane with Acid Chlorides: Highly Efficient Synthesis of α-Oxo Amides

Silyl Tether-Assisted Photooxygenation of Electron-Deficient Enaminoesters: Direct Access to Oxamate Formation

Photooxygenation reactions of electron-deficient enaminoesters bearing an oxophilic silyl tether at the α-position of the nitrogen atom using methylene blue (MB) were explored to develop a mild and efficient photochemical strategy for oxidative C-C double bond cleavage reactions via singlet oxygen (¹O₂). Photochemically generated ¹O₂, through energy transfer from the triplet excited state of MB (³MB*) to molecular oxygen (³O₂), was added across a C-C double bond moiety of enaminoesters to form perepoxides, which rearranged to form dioxetane intermediates. The cycloreversion of the formed dioxetane via both C-C and O-O bond cleavage processes led to the formation of oxamates. Importantly, contrary to alkyl group tether-substituted electron-deficient enaminoesters that typically disfavor photooxygenation, the silyl tether-substituted analogues undergo this photochemical transformation efficiently with the assistance of a silyl tether, which facilitates formation of the perepoxide. The observations in this study provide useful information about photosensitized oxygenation reactions of unsaturated C-C bonds, and, moreover, this photochemical strategy can be utilized as a mild and feasible method for the preparation of diversely functionalized carbonyl compounds including oxamates.

A copper iodide-catalyzed coupling reaction of benzofuran-3(2H)-ones with amines: an approach to α-ketoamides

A CuI-catalyzed coupling reaction of benzofuran-3(2H)-ones with amines has been well established for the direct synthesis of α-ketoamides. This process involves C-O bond cleavage and C[double bond, length as m-dash]O/C-N bond formation. Mechanism studies indicated that this α-ketoamide formation reaction may involve a free radical process.

Pd/C-catalyzed synthesis of oxamates by oxidative cross double carbonylation of alcohols and tertiary amines through C–N bond cleavage

Palladium-catalyzed oxidative cross double carbonylation reaction between tertiary amines and alcohols using oxidant O₂ and KI as the additive affords oxamates. Oxamate are as a intermediate in biological active compound and glycol synthesis.

Visible-Light-Promoted Oxidative Amidation of Bromoalkynes with Anilines: An Approach to α-Ketoamides

A convenient and practical synthetic route to α-ketoamides from bromoalkynes and anilines through phototriggered organic transformations via a C-N cross-coupling and an oxidation of C≡C was developed. The reaction could be furnished without an external photocatalyst at ambient conditions, and a wide range of α-ketoamides were obtained in good yields.

Transition metal-free synthesis of α-ketoamides from arylmethyl ketones and alkylphosphoramides

Synthesis of α-ketoamides from arylmethyl ketones and hexalkylphosphoramides using TBAI as the catalyst and TBHP as the oxidant.

Room temperature copper-catalyzed oxidative amidation of terminal alkynes for the synthesis of α-ketoamides using O-benzoyl hydroxylamines as aminating reagent and oxidant

A novel and convenient copper-catalyzed oxidative amidation for the synthesis of α-ketoamides has been successfully developed, which uses easily available O-benzoyl hydroxylamines as aminating reagent and oxidant.

Metal free one-pot synthesis of α-ketoamides from terminal alkenes

A practical approach towards the synthesis of α-ketoamides from terminal alkenes has been developed using I₂/IBX under one-pot reaction conditions.

Metal-free in situ sp3, sp2, and sp C–H functionalization and oxidative cross coupling with benzamidines hydrochloride: a promising approach for the synthesis of α-ketoimides

A new metal-free tandem protocol for the synthesis of α-ketoimides via sp³, sp², and sp C–H functionalization followed by oxidative cross coupling with benzamidines hydrochloride using catalytic iodine with TBHP in DMSO has been developed.

OxymaPure/DIC: an efficient reagent for the synthesis of a novel series of 4-[2-(2-acetylaminophenyl)-2-oxo-acetylamino] benzoyl amino acid ester derivatives

OxymaPure (ethyl 2-cyano-2-(hydroxyimino)acetate) was tested as an additive for use in the carbodiimide (DIC) approach for the synthesis of a novel series of α-ketoamide derivatives (4-[2-(2-acetylaminophenyl)-2-oxo-acetylamino]benzoyl amino acid ester derivatives). OxymaPure showed clear superiority to HOBt/DIC or carbodiimide alone in terms of purity and yield. The title compounds were synthesized via the ring opening of N-acylisatin. First, N-acetylisatin was reacted with 4-aminobenzoic acid under conventional heating as well as microwave irradiation to afford 4-(2-(2-acetamidophenyl)-2-oxoacetamido)benzoic acid. This α-ketoamide was coupled to different amino acid esters using OxymaPure/DIC as a coupling reagent to afford 4-[2-(2-acetylaminophenyl)-2-oxo-acetylamino]benzoyl amino acid ester derivatives in excellent yield and purity. The synthesized compounds were characterized using FT-IR, NMR, and elemental analysis.

An Efficient and Mild Method for the Synthesis and Hydrazinolysis ofN-Glyoxylamino Acid Esters

N-Glyoxylamino acid ester derivatives were synthesized via the ring opening ofN-acetylisatin using moderate conditions. During the hydrazinolysis ofN-glyoxylamino acid ester derivatives with hydrazine hydrate (80%) in methanol, unexpected reduction of theα-keto group occurred to affordN-acylamino acid hydrazide derivatives in good yield (80–90%) (Wolff-Kishner type reaction). All the synthesized compounds were characterized by1H NMR,13C NMR, and elemental microanalysis.

Selenium dioxide-mediated synthesis of α-ketoamides from arylglyoxals and secondary amines

A facile and expeditious synthetic approach to α-ketoamides 3 is described. A series of α-ketoamides 3 was synthesized via reaction of selenium dioxide-mediated oxidative amidation between arylglyoxals 1 and secondary amines 2, and accelerated with microwave irradiation. Our findings indicate that constrained amines, such as piperazine and piperidine exhibit higher conversions for this transformation. This reaction was explored by synthesizing a series of α-ketoamides 3 from various arylglyoxals with cyclic and acyclic secondary amines.

Synthesis of alpha-keto-imides via oxidation of ynamides

A de novo preparation of alpha-keto-imides via ynamide oxidation is described. With a number of alkyne oxidation conditions screened, a highly efficient RuO2-NaIO4 mediated oxidation and a DMDO oxidation have been identified to tolerate a wide range of ynamide types. In addition to accessing a wide variety of alpha-keto-imides, the RuO2-NaIO4 protocol provides a novel entry to the vicinal tricarbonyl motif via oxidation of push-pull ynamides, and imido acylsilanes from silyl-substituted ynamides. Chemoselective oxidation of ynamides containing olefins can be achieved by using DMDO, while the RuO2-NaIO4 protocol is not effective. These studies provide further support for the synthetic utility of ynamides.

The potential of P1 site alterations in peptidomimetic protease inhibitors as suggested by virtual screening and explored by the use of C-C-coupling reagents

A synthetic concept is presented that allows the construction of peptide isostere libraries through polymer-supported C-acylation reactions. A phosphorane linker reagent is used as a carbanion equivalent; by employing MSNT as a coupling reagent, the C-acylation can be conducted without racemization. Diastereoselective reduction was effected with L-selectride. The reagent linker allows the preparation of a norstatine library with full variation of the isosteric positions including the P1 side chain that addresses the protease S1 pocket. Therefore, the concept was employed to investigate the P1 site specificity of peptide isostere inhibitors systematically. The S1 pocket of several aspartic proteases including plasmepsin II and cathepsin D was modeled and docked with approximately 500 amino acid side chains. Inspired by this virtual screen, a P1 site mutation library was designed, synthesized, and screened against three aspartic proteases (plasmepsin II, HIV protease, and cathepsin D). The potency of norstatine inhibitors was found to depend strongly on the P1 substituent. Large, hydrophobic residues such as biphenyl, 4-bromophenyl, and 4-nitrophenyl enhanced the inhibitory activity (IC50) by up to 70-fold against plasmepsin II. In addition, P1 variation introduced significant selectivity, as up to 9-fold greater activity was found against plasmepsin II relative to human cathepsin D. The active P1 site residues did not fit into the crystal structure; however, molecular dynamics simulation suggested a possible alternative binding mode.