Practical and efficient synthesis of N-halo compounds

N-Sulfenylation of β-Lactams: Radical Reaction of N-Bromo-azetidinones by TEMPO Catalysis

Azetidinones with a sulfenyl group on the β-lactam nitrogen atom show interesting biological activities as antimicrobial agents and enzyme inhibitors. We report in the present study a versatile synthesis of N-sulfenylated azetidinones starting from the corresponding N-bromo derivatives by means of the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) radical as the catalyst and disulfides. Preparation of N-halo-azetidinones was studied and optimized. The reactivity of N-bromo-azetidinone 2a as a model compound in the presence of TEMPO radical was investigated by NMR and electron paramagnetic resonance (EPR) spectroscopy studies. Optimization of the reaction conditions allowed the access of N-alkylthio- or N-arylthio-azetidinones from 55 to 92% yields, and the method exhibited a good substrate scope.

Synthesis and Antioxidative Properties of 1,2,3,4-Tetrahydropyridine Derivatives with Different Substituents in 4-Position

Natural products are an excellent source of inspiration for the development of new drugs. Among them, betalains have been extensively studied for their antioxidant properties and potential application as natural food dyes. Herein, we describe the seven-step synthesis of new betalamic acid analogs without carboxy groups in the 2- and 6-position with an overall yield of ~70%. The Folin–Ciocalteu assay was used to determine the antioxidant properties of protected intermediate 21. Additionally, the five-step synthesis of betalamic acid analog 35 with three ester moieties was performed. Using NMR techniques, the stability of the obtained compounds towards oxygen was analyzed.

The (±)-6-Aza[1.0]triblattane Skeleton: Contraction beyond the Wilder-Culberson Ring System

Synthesis of the 6-aza[1.0]triblattane skeleton and the unexpected construction of the 7-azatetracyclo[4.2.1.0^2,5.0^3,7]nonane framework are reported, as inspired by the Wilder-Culberson 1-aza[1.1]triblattane ring system. The key steps to assess the 6-aza[1.0]triblattane include accessing the 1,6-cycloaddition product from reaction of chlorosulfonyl isocyanate with cyclohept-1,3,5-triene followed by intramolecular electrocyclization and aminium radical cyclization.

Recent advances in the synthesis of organic chloramines and their insights into health care

Organic nitrogen–chlorine compounds and their derivatives are important heterocyclic motifs, exhibiting applications such as N-chlorinating agents, analytical reagents, disinfectants, antipathogens, and as synthetic intermediates for drugs, polymers, and natural products.

A general and atom-efficient continuous-flow approach to prepare amines, amides and imines via reactive N-chloramines

Chloramines are an important class of reagents, providing a convenient source of chlorine or electrophilic nitrogen. However, the instability of these compounds is a problem which makes their isolation and handling difficult. To overcome these hazards, a continuous-flow approach is reported which generates and immediately reacts N-chloramines directly, avoiding purification and isolation steps. 2-Chloramines were produced from the reaction of styrenes with N-alkyl-N-sulfonyl-N-chloramines, whilst N-alkyl or N,N'-dialkyl-N-chloramines reacted with anisaldehyde in the presence of t-BuO2H oxidant to afford amides. Primary and secondary imines were produced under continuous conditions from the reaction of N-chloramines with base, with one example subsequently reduced under asymmetric conditions to produce a chiral amine in 94% ee.

Chemoselective Acylation of Primary Amines and Amides with Potassium Acyltrifluoroborates under Acidic Conditions

Current methods for constructing amide bonds join amines and carboxylic acids by dehydrative couplings-processes that usually require organic solvents, expensive and often dangerous coupling reagents, and masking other functional groups. Here we describe an amide formation using primary amines and potassium acyltrifluoroborates promoted by simple chlorinating agents that proceeds rapidly in water. The reaction is fast at acidic pH and tolerates alcohols, carboxylic acids, and even secondary amines in the substrates. It is applicable to the functionalization of primary amides, sulfonamides, and other N-functional groups that typically resist classical acylations and can be applied to late-stage functionalizations.

Oxidative Rearrangement via in Situ Generated N-Chloroamine: Synthesis of Fused Tetrahydroisoquinolines

An oxidative rearrangement reaction of spiro tetrahydroisoquinolines has been developed for the synthesis of fused tetrahydroisoquinolines using in situ generated N-chloroamines. The reaction proceeds via initial chlorination of an amine, followed by a 1,2-carbon to nitrogen migration, and nucleophilic trapping of a ketiminium ion intermediate in a one-pot operation. The electrophilic nature of N-chloroamines allowed for the carbon-nitrogen bond formation in this reation.

Continuous formation of N-chloro-N,N-dialkylamine solutions in well-mixed meso-scale flow reactors

The continuous flow synthesis of a range of organic solutions of N,N-dialkyl-N-chloramines is described using either a bespoke meso-scale tubular reactor with static mixers or a continuous stirred tank reactor. Both reactors promote the efficient mixing of a biphasic solution of N,N-dialkylamine in organic solvent, and aqueous sodium hypochlorite to achieve near quantitative conversions, in 72–100% in situ yields, and useful productivities of around 0.05 mol/h with residence times from 3 to 20 minutes. Initial calorimetric studies have been carried out to inform on reaction exotherms, rates and safe operation. Amines which partition mainly in the organic phase require longer reaction times, provided by the CSTR, to compensate for low mass transfer rates in the biphasic system. The green metrics of the reaction have been assessed and compared to existing procedures and have shown the continuous process is improved over previous procedures. The organic solutions of N,N-dialkyl-N-chloramines produced continuously will enable their use in tandem flow reactions with a range of nucleophilic substrates.

Combining organometallic reagents, the sulfur dioxide surrogate DABSO, and amines: a one-pot preparation of sulfonamides, amenable to array synthesis

We describe a method for the synthesis of sulfonamides through the combination of an organometallic reagent, a sulfur dioxide equivalent, and an aqueous solution of an amine under oxidative conditions (bleach). This simple reaction protocol avoids the need to employ sulfonyl chloride substrates, thus removing the limitation imposed by the commercial availability of these reagents. The resultant method allows access to new chemical space, and is also tolerant of the polar functional groups needed to impart favorable physiochemical properties required for medicinal chemistry and agrochemistry. The developed chemistry is employed in the synthesis of a targeted 70 compound array, prepared using automated methods. The array achieved a 93% success rate for compounds prepared. Calculated molecular weights, lipophilicities, and polar surface areas are presented, demonstrating the utility of the method for delivering sulfonamides with drug-like properties.

Recent progress in copper-catalyzed electrophilic amination

This perspective encompasses the recent trends and developments in copper-catalyzed electrophilic amination for the construction of various amines and their derivatives.

Nitrogen-centered radical-mediated C–H imidation of arenes and heteroarenes via visible light induced photocatalysis

Visible light-induced photocatalytic aromatic C–H imidation with N-chlorophthalimide proceeds through a nitrogen-centered radical intermediate to furnish the corresponding N-aryl products.

Insertion of arynes into N-halo bonds: a direct approach to o-haloaminoarenes

A new approach to access o-haloaminoarenes has been achieved by insertion of arynes into a nitrogen-halide bond (N-X). This transition-metal-free transformation displays a broad substrate scope of arynes, good compatibility with functional groups, and high regioselectivity. Representative transformations of the o-haloaminoarenes are described to highlight their utility for rapid access to diversely functionalized aminoarene derivatives.

Umpolung reactivity in amide and peptide synthesis

The amide bond is one of nature's most common functional and structural elements, as the backbones of all natural peptides and proteins are composed of amide bonds. Amides are also present in many therapeutic small molecules. The construction of amide bonds using available methods relies principally on dehydrative approaches, although oxidative and radical-based methods are representative alternatives. In nearly every example, carbon and nitrogen bear electrophilic and nucleophilic character, respectively, during the carbon-nitrogen bond-forming step. Here we show that activation of amines and nitroalkanes with an electrophilic iodine source can lead directly to amide products. Preliminary observations support a mechanism in which the polarities of the two reactants are reversed (German, umpolung) during carbon-nitrogen bond formation relative to traditional approaches. The use of nitroalkanes as acyl anion equivalents provides a conceptually innovative approach to amide and peptide synthesis, and one that might ultimately provide for efficient peptide synthesis that is fully reliant on enantioselective methods.

Umpolung amination: nickel-catalyzed coupling reactions of N,N-dialkyl-N-chloroamines with diorganozinc reagents

N,N-dialkyl-N-chloroamines are an effective source of electrophilic nitrogen for nickel-catalyzed coupling with diarylzinc reagents. A variety of N-chloroamines as well as organozinc reagents react smoothly under the reaction conditions. A one-pot procedure that circumvents the need to isolate the N-chloroamines is described.

Catalytic asymmetric synthesis of an HIV integrase inhibitor

An efficient synthesis of HIV integrase inhibitor (S)-(-)-1 via a unique asymmetric hydrogenation of a mixture of imines/enamine 5a-5b/5c is described. Hydrogenation of the imines/enamine by a Rh(I)-Josiphos complex afforded 6 in 90% yield and 90% ee. Amide formation completed the synthesis of 1 in 58% overall yield from 2, which is readily available from 3,4-dihydro-2H-pyran in a seven-step sequence. A deuterium labeling study suggests the asymmetric hydrogenation proceeds predominantly via the enamine tautomer.