Organocatalytic Enantioselective Formal [4 + 2] Cycloaddition of Enones with Cyclic N-Sulfonylimines and Methylene Chromene for Chiral Spirocyclic Compounds

Enantioselective Mannich Reaction between Cyclic N-Sulfonyl Ketimines and Isatin-Derived Ketimines

An enantioselective Mannich reaction with cyclic N-sulfonyl ketimines as the nucleophiles was developed. In the presence of 5 mol % chiral thiourea catalyst C11, the asymmetric Mannich reaction between cyclic N-sulfonyl ketimines and isatin-derived ketimines was achieved in high yields and good-to-excellent enantioselectivities (84-99% yields with 75-99.8% ee). This methodology provided an effective route to construct chiral 3-amino-2-oxindoles containing a cyclic N-sulfonyl ketimine scaffold. The initial biological evaluation of the products in cell-based assays demonstrated that some compounds have excellent antiproliferative activity against human osteosarcoma cells.

Derivatives of 4-methyl-1,2,3-benzoxathiazine 2,2-dioxide as selective inhibitors of human carbonic anhydrases IX and XII over the cytosolic isoforms I and II

A series of 4-methyl-1,2,3-benzoxathiazine-2,2-dioxides with various substituents in 5, 6 or 7 positions was obtained from corresponding 2'-hydroxyacetophenones in their reaction with sulphamoyl chloride. 6- and 7-aryl substituted 4-methyl-1,2,3-benzoxathiazine-2,2-dioxides were obtained from aryl substituted 2'-hydroxyacetophenonesprepared from 4- or 5-bromo-2'-hydroxyacetophenones via two-step protocol. 4-Methyl-1,2,3-benzoxathiazine-2,2-dioxides were investigated as inhibitors of four human (h) carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, off-target cytosolic hCA I and II, and target transmembrane, tumour-associated hCA IX and XII. Twenty derivatives of 4-methyl-1,2,3-benzoxathiazine 2,2-dioxide were obtained. With one exception (compound2a), they mostly act as nanomolar inhibitors of target hCA IX and XII. Basically, all screened compounds express none or low inhibitory properties towards off-target hCA I. hCA II is inhibited in micromolar range. Overwhelming majority of 4-methyl-1,2,3-benzoxathiazine 2,2-dioxides express excellent selectivity towards CA IX/XII over hCA I as well as very good selectivity towards CA IX/XII over hCA II.

Recent synthetic strategies toward the synthesis of spirocyclic compounds comprising six-membered carbocyclic/heterocyclic ring systems

Spirocyclic compounds fascinate the synthetic chemists due to their privileged ring system and efficacy in drug discovery. Many natural compounds comprise spirocyclic moiety in their skeleton and are effective in pharmaceutical industry. Over the years, many synthetic methodologies have been established for the construction of spirocyclic compounds. In this review, recent synthetic approaches to accessing various spirocompounds comprising six-membered carbocycles/heterocycles have been summarized.

Unmasking the reverse reactivity of cyclic N-sulfonyl ketimines: multifaceted applications in organic synthesis

The chemistry related to the exploration of cyclic N-sulfonyl ketimines and their derivatives has attracted significant attention in the last few decades because of their intriguing structures and properties. They serve broadly as reactive synthons in various reactions to create a diverse set of synthetically and biologically attractive molecules. Furthermore, these moieties, which possess multiple heteroatoms (N, O and S), display or can enhance many biological activities. In the case of synthetic reactions, chemists mainly focus on the chemical manipulation of the highly reactive prochiral CN bond of N-sulfonyl ketimines. Besides their traditional role as electrophiles, N-sulfonyl ketimines possess α-Csp³-H protons, and thus behave as potential carbonucleophiles, where they can undergo several C-X (X = C, N and O) bond-forming reactions with different types of electrophiles under various conditions to form a wide range of fascinating asymmetric and non-asymmetric versions of fused heterocycles, carbocycles, spiro-fused skeletons, pyridines, pyrroles, etc. Herein, we highlight the recent examples from our research work and others covering the scope of cyclic N-sulfonyl ketimines as useful carbonucleophiles. In addition, the detailed mechanistic studies of the above-mentioned reactions are also presented.

Contrasting Carboannulation Involving δ-Acetoxy Allenoate as a Four-Carbon Synthon Using DABCO and DMAP: Access to Spiro-carbocyclic and m-Teraryl Scaffolds

Spiro-annulation involving δ-acetoxy allenoate and alkyl benzoisothiazole dioxide (N-sulfonyl ketimine) triggered by DABCO/MeCO₂H combination leads to an essentially single diastereomer via chemo- and regiospecific [4 + 2]-carboannulation and a new hydroxyl group is introduced. In contrast, DMAP-catalyzed benzannulation using the same reactants affords unsymmetrical m-teraryls via Mannich coupling, sequential proton transfers, and C-N bond cleavage. Here, δ-acetoxy allenoate serves as a 4C-synthon and the carboannulation is completely base dependent and mutually exclusive.

The dual alkylation of the C(sp3)–H bond of cyclic α-methyl-N-sulfonyl imines via the sequential condensation/hydride transfer/cyclization process

The dual alkylation of the C(sp³)–H bond of the cyclic α-methyl-N-sulfonyl imine has been achieved through the piperidine-promoted cascade condensation/[1,5]-hydride transfer/cyclization from cyclic α-methyl-N-sulfonyl imine and o-aminobenzaldehyde in trifluoroethanol.

Selective construction of functionalized chromeno[3,4-b]pyrroles and benzo[c]chromenesviaa K3PO4promoted three-component reaction

A K₃PO₄promoted three-component reaction of pivaloylacetonitrile (benzoylacetonitrile), dialkyl but-2-ynedioates and 2-aryl-3-nitrochromenes afforded functionalized chromeno[3,4-b]pyrroles.

Primary amine catalyzed diastereo- and enantioselective Michael reaction of thiazolones and α,β-unsaturated ketones

The chiral primary amine catalyzed asymmetric Michael reaction of thiazolones and α,β-unsaturated ketones was reported. Two different optimal catalytic systems were obtained corresponding to cyclic and linear α,β-unsaturated ketones. By employing chiral primary amines as the catalysts and amino-acid derivatives as the additives, a variety of Michael adducts containing the scaffold of the thiazole ring were prepared in moderate to good yields and with excellent diastereo- and enantioselectivities (up to 95% yield, all up to >19/1 dr, up to 96% ee). The reaction was scaled up to obtain 1.73 grams of the Michael adduct with the maintenance of yield and stereoselectivity.

Asymmetric Organocatalyzed Reaction Sequence To Synthesize Chiral Bridged and Spiro-Bridged Benzofused Aminals via Divergent Pathways

A highly efficient asymmetric organocatalysis-triggered reaction sequence is developed. 2-Hydroxy cinnamaldehydes and cyclic N-sulfonyl ketimines were both used as multisite substrates (more than two reactive sites) to access structurally diverse chiral bridged and spiro-bridged benzofused aminal derivatives, where an inseparable equilibrating mixture of isomers can be regioselectively converted into bridged benzofused aminals with different ring connectivities via divergent pathways. Several stereoselective transformations of the resulted bridged aminals are presented.

Asymmetric synthesis of highly functionalized furanones via direct Michael reactions mediated by a bulky primary amine

A bulky chiral primary amine catalyzed Michael reaction of 3(2H)-furanones has been realized, leading to the construction of substituted furanone derivatives.

Asymmetric Dearomative Formal [4 + 2] Cycloadditions of N,4-Dialkylpyridinium Salts and Enones To Construct Azaspiro[5.5]undecane Frameworks

The asymmetric dearomative formal [4 + 2] cycloaddition reaction of activated N,4-dialkylpyridinium salts and acyclic α,β-unsaturated ketones was developed by the cascade iminium ion-enamine catalysis of a cinchona-derived amine. A spectrum of valuable azaspiro[5.5]undecane architectures was efficiently constructed with high to excellent diastereoselectivity and enantioselectivity.

New development in the enantioselective synthesis of spiro compounds

In this review we summarize the latest developments in the enantioselective synthesis of spirocompounds. The most important organometallic and organocatalytic methodologies are highlighted.

Asymmetric [4+2] annulations to construct norcamphor scaffolds with 2-cyclopentenone via double amine–thiol catalysis

A double catalytic system combining chiral amine and 2-mercaptobenzoic acid is applied for α′,β-regioselective [4+2] annulations of 2-cyclopentenone with diverse activated alkenes.

Molecular diversity of the domino annulation reaction of 2-aryl-3-nitrochromenes with pivaloylacetonitriles

In the presence of triethylamine, the domino annulation reaction of two molecules of pivaloylacetonitrile with one molecule of 2-aryl-3-nitrochromene in tetrahydrofuran resulted in the unprecedented imino-substituted dihydrofuro[2,3-c]chromene derivatives in high yields.

Diastereoselective synthesis of benzo[d]chromeno[3′,4′:3,4]pyrrolo[2,1-b]thiazoles via cycloaddition reaction of benzothiazolium salts with 3-nitrochromenes

Diastereospecific synthesis of benzo[d]chromeno[3′,4′:3,4]pyrrolo[2,1-b]thiazoles via cycloaddition reaction of benzothiazolium salts with 3-nitrochromenes.

Remote stereocontrolled asymmetric 1,6-addition/1,4-addition cascade reactions between cyclic dienones and 2-indolinethiones

Enantioselective 1,6-addition/1,4-addition cascade reactions between cyclic dienones and 2-indolnethiones have been realized, affording chiral spiro[thiopyranoindole-cyclohexanone] scaffolds facilely and efficiently.