Base-mediated intramolecular C- and N-arylation of N,N-disubstituted 2-nitrobenzenesulfonamides: advanced intermediates for the synthesis of diverse nitrogenous heterocycles

Synthesis of Medium-Ring-Sized Benzolactams by Using Strong Electrophiles and Quantitative Evaluation of Ring-Size Dependency of the Cyclization Reaction Rate

Benzolactams with medium-sized rings were synthesized via the electrophilic aromatic substitution reaction of carbamoyl cations (R₁R₂N⁺═C═O) in good to high yields without dilution. These reactions were utilized to quantitatively examine the extent of retardation of medium-sized ring formation, compared to five- or six-membered ring formation. The order of reaction rates of formation of cyclic benzolactams is six- > five- > seven- > eight- > nine-membered ring at 25 °C. The present reaction provides a route to eight- and nine-membered benzolactams.

Arylation and alkenylation of activated alkyl halides using sulfonamides

A variety of quaternary aryl amino acid derivatives can be synthesised using tandem S_N2/Smiles rearrangement chemistry involving aryl sulfonamides and α-chloro carbonyl compounds.

Traceless Solid-Phase Organic Synthesis

Traceless solid-phase synthesis represents an ultimate sophisticated synthetic strategy on insoluble supports. Compounds synthesized on solid supports can be released without a trace of the linker that was used to tether the intermediates during the synthesis. Thus, the target products are composed only of the components (atoms, functional groups) inherent to the target core structure. A wide variety of synthetic strategies have been developed to prepare products in a traceless manner, and this review is dedicated to all aspects of traceless solid-phase organic synthesis. Importantly, the synthesis does not need to be carried out on a linker designed for traceless synthesis; most of the synthetic approaches described herein were developed using standard, commercially available linkers (originally devised for solid-phase peptide synthesis). The type of structure prepared in a traceless fashion is not restricted. The individual synthetic approaches are divided into eight sections, each devoted to a different methodology for traceless synthesis. Each section consists of a brief outline of the synthetic strategy followed by a description of individual reported syntheses.

Unified Approach to the Chemoselective α-Functionalization of Amides with Heteroatom Nucleophiles

Functionalization at the α-position of carbonyl compounds has classically relied on enolate chemistry. As a result, the generation of a new C–X bond, where X is more electronegative than carbon requires an oxidation event. Herein we show that, by rendering the α-position of amides electrophilic through a mild and chemoselective umpolung transformation, a broad range of widely available oxygen, nitrogen, sulfur, and halogen nucleophiles can be used to generate α-functionalized amides. More than 60 examples are presented to establish the generality of this process, and calculations of the mechanistic aspects underline a fragmentation pathway that accounts for the broadness of this methodology.

Traceless Solid-Phase Synthesis of 1' H-Spiro[Pyrrolidine-3,2'-quinazolin]-2-ones and 1' H-Spiro[Piperidine-3,2'-quinazolin]-2-ones via Lactamization of 1,2-Dihydroquinazoline-2-carboxylates

We present the solid-phase synthesis of 1,2-dihydroquinazoline-2-carboxylate derivatives with a quaternary carbon in position 2 and their subsequent cyclization in solution into compounds with unique 3D architectures and pharmacological relevance-spiroquinazolines, namely, 1' H-spiro[pyrrolidine-3,2'-quinazolin]-2-ones and 1' H-spiro[piperidine-3,2'-quinazolin]-2-ones. Acyclic precursors were prepared from commercially available building blocks: protected amino acids (2,4-diaminobutyric acid and ornithine), 2-nitrobenzensulfonyl chlorides and α-bromoacetophenones. The crucial step of the synthesis was a base-mediated tandem reaction including C-arylation followed by cyclization into indazole oxides, and the formation of a 5-membered heterocycle was accomplished by ring expansion into quinazolines. These derivatives were cyclized into spiro compounds in solution after cleavage from the resin.

Stereoselective Polymer-Supported Synthesis of Morpholine- and Thiomorpholine-3-carboxylic Acid Derivatives

Herein we report the polymer-supported synthesis of 3,4-dihydro-2H-1,4-oxazine-3-carboxylic acid derivatives using immobilized Fmoc-Ser(tBu)-OH and Fmoc-Thr(tBu)-OH as the starting materials. After the solid-phase-synthesis of N-alkyl-N-sulfonyl/acyl intermediates, the target dihydrooxazines were obtained using trifluoroacetic acid-mediated cleavage from the resin. This approach was also studied for the preparation of dihydrothiazines from immobilized Fmoc-Cys(Trt)-OH. Inclusion of triethylsilane in the cleavage cocktail resulted in the stereoselective formation of the corresponding morpholine/thiomorpholine-3-carboxylic acids. Stereochemical studies revealed the specific configuration of the newly formed stereocenter and also the formation of stable N-acylmorpholine rotamers.

N-Oxide as an Intramolecular Oxidant in the Baeyer-Villiger Oxidation: Synthesis of 2-Alkyl-2H-indazol-3-yl Benzoates and 2-Alkyl-1,2-dihydro-3H-indazol-3-ones

In this study, we describe the intramolecular Baeyer-Villiger oxidation of ketones to esters using N-oxide. 2-Nitro-N-alkyl-N-(2-oxo-2-phenylethyl)benzenesulfonamide compounds are known to undergo base-mediated C-arylation followed by N-N bond formation, producing unstable five-membered ring intermediates that spontaneously dehydrate to indazole oxides. We identified the reaction conditions under which the cyclic intermediate undergoes acid-mediated intramolecular Baeyer-Villiger oxidation of the ketone in which N-oxide serves as the intramolecular oxidizing agent. The solid-phase synthesis plays a critical role in the successful transformation, allowing rapid access to the unstable but Baeyer-Villiger oxidation-prone intermediate. This synthetic route provides practical access to 2-alkyl-2H-indazol-3-yl benzoates and 2-alkyl-1,2-dihydro-3H-indazol-3-ones, which are known privileged structures possessing remarkable diverse pharmacologically relevant activities.

Mining the Chemical Space: Application of 2/4-Nitrobenzenesulfonamides in Solid-Phase Synthesis

Polymer-supported benzenesulfonamides prepared from various immobilized primary amines and 2/4-nitrobenzenesulfonyl chloride have been used as key intermediates in different chemical transformations, including unusual rearrangements to yield a number of diverse privileged scaffolds. This review summarizes individual strategies in their application to date.

3-Alkyl-3-(alkylamino)indolin-2-ones via Base-Mediated C-Arylation of 2-Nitrobenzenesulfonamides

Resin-bound intermediates prepared from polymer-supported amino acid esters, 2-nitrobenezenesulfonyl chlorides, and alcohols were used to synthesize 3-alkyl-3-(alkylamino) indolin-2-ones. The key step of the reaction sequence was the formation of a quaternary carbon via the base-mediated C-arylation of 2-nitrobenzenesulfonamides. The cleavage of the acyclic precursors from the resin and subsequent reduction of the nitro group by Zn in acetic acid triggered the spontaneous cyclization of the arylated compounds to indolinones. The synthesis was carried out using simple commercially available building blocks under mild conditions and provided the 3,3-disubstituted indolinone derivatives with good overall yields however, the arylation reaction resulted in the epimerization of the quaternary carbon.

Aryne generation vs. Truce-Smiles and fries rearrangements during the Kobayashi fragmentation reaction: a new bi-aryl synthesis

Treatment of (ortho-trimethysilyl)aryl phenylsulfonates with fluoride anion initiates a Truce-Smiles rearrangement leading to the formation of bi-aryls.