IntraMolecular Diels–Alder Reactions of Vinylarenes and Alkynyl Arenes (the IMDAV Reaction)

Crystal structure and Hirshfeld surface analysis of (Z)-4-oxo-4-{phen-yl[(thio-phen-2-yl)meth-yl]amino}-but-2-enoic acid

In the title compound, C15H13NO3S, the mol-ecular conformation is stable with the intra-molecular O-H⋯O hydrogen bond forming a S(7) ring motif. In the crystal, mol-ecules are connected by C-H⋯O hydrogen bonds, forming C(8) chains running along the a-axis direction. Cohesion of the packing is provided by weak van der Waals inter-actions between the chains. A Hirshfeld surface analysis was undertaken to investigate and qu-antify the inter-molecular inter-actions. The thio-phene ring is disordered in a 0.9466 (17):0.0534 (17) ratio over two positions rotated by 180°.

Room Temperature Diels-Alder Reactions of 4-Vinylimidazoles

In the course of studying Diels-Alder reactions of 4-vinylimidazoles with N-phenylmaleimide, it was discovered that they engage in cycloaddition at room temperature to give high yields of the initial cycloadduct as a single stereoisomer. In certain cases, the product precipitated out of the reaction mixture and could be isolated by simple filtration, thereby avoiding issues with aromatization observed during chromatographic purification. Given these results, intramolecular variants using doubly activated dienophiles were also investigated at room temperature. Amides underwent cycloaddition at room temperature in modest yields, but the initial adducts were not isolable with Nimid-benzyl-protected systems. Attempts to extend these results to the corresponding esters and hydroxamate were less successful with these substrates only undergoing cycloaddition at elevated temperatures in lower yields. Density functional theory calculations were performed to evaluate the putative transition states for both the inter- and intramolecular variants to rationalize experimental observations.

One-Pot Reaction Sequence: N-Acylation/Pictet-Spengler Reaction/Intramolecular [4 + 2] Cycloaddition/Aromatization in the Synthesis of β-Carboline Alkaloid Analogues

One-pot synthesis of tetrahydro-β-carbolines, fused with an isoindole core, was proposed starting from maleic anhydride and azomethines easily available from tryptamines and 3-(hetaryl)acroleins. This sequence includes four key steps: an acylation of the aldimine with maleic anhydride, a Pictet-Spengler cyclization, an intramolecular Diels-Alder reaction, and a concluding [1,3]-H shift. As a result, six- or seven-nuclear alkaloid-like heterocyclic systems, containing a benzo[1,2]indolizino[8,7-b]indole fragment annulated with furan, thiophene, or pyrrole, are formed in a diastereoselective manner.

Crystal structure and Hirshfeld surface analysis of 10-hy-droxy-2-(4-meth-oxy-phen-yl)-3-oxo-2,3,3a,4,10,10a-hexa-hydro-1H-9-thia-2-aza-cyclo-penta-[b]fluorene-4-carb-oxy-lic acid dimethyl sulfoxide-d6 monosolvate

In the title compound, C22H19NO5S·C2D6OS, the central six-membered ring has a slightly distorted boat conformation, while the fused pyrrolidine ring adopts an envelope conformation. These conformations are stabilized by O-H⋯O hydrogen bonds between the main compound and solvent mol-ecules. In addition, intra-molecular C-H⋯O hydrogen bonds in the main mol-ecule form two S(6) rings. Mol-ecules are connected by pairs of inter-molecular C-H⋯O hydrogen bonds, forming dimers with a R 2 2(8) motif. These dimers form a three-dimensional network through O-H⋯O, O-H⋯S and C-H⋯O hydrogen bonds with each other directly and through solvent mol-ecules. In addition, weak π-π stacking inter-actions [centroid-to-centroid distances = 3.9937 (10) and 3.9936 (10) Å, slippages of 2.034 and 1.681 Å] are observed. The inter-molecular contacts were qu-anti-fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H⋯H 41.7%, O⋯H/H⋯O 27.7%, C⋯H/H⋯C 17.0%, and S⋯H/H⋯S 7.5%.

Domino Three-Component N-Acylation/[4 + 2] Cycloaddition/Alder-ene Synthesis of Polysubstituted Benzo[f]isoindole-4-carboxylic Acids

Diversely substituted, partially saturated benzo[f]isoindole-4-carboxylic acids were synthesized by a new three-component reaction (3CR) starting from cinnamic amines (3-arylallylamines), maleimides, and maleic anhydride. The process consists of N-acylation of the amines by maleic anhydride, intramolecular [4 + 2] cycloaddition in vinylarenes (the IMDAV reaction), and the concluding Alder-ene reaction between Diels-Alder intermediates and maleimides. All of the reaction steps proceed in a highly regio- and stereoselective manner, furnishing five adjacent chiral centers and leading to a single diastereoisomer of the title compound. The efficiency of the transformation is secured by thermal conditions or utilization of soft Lewis acids (Yb(OTf)3) as catalysts. The kinetics and mechanism of the 3CR were studied by using dynamic 19F NMR. Based on the NMR data and density functional theory (DFT) calculations, the IMDAV, not the Alder-ene, reaction is the rate-limiting step of the entire process.

Crystal structure and Hirshfeld surface analysis of 4-cyano-N-[(4-cyano-phen-yl)sulfon-yl]-N-[2-(5-methyl-furan-2-yl)phen-yl]benzene-sulfonamide

In the title compound, C25H17N3O5S2, intra-molecular π-π inter-actions [centroid-to-centroid distance = 3.5640 (9) Å] are observed between the furan and benzene rings of the 4-cyano-phenyl group. In the crystal, mol-ecules are connected via C-H⋯O and C-H⋯N hydrogen bonds, forming layers parallel to the (100) plane. These layers are inter-connected by C-H⋯π inter-actions and weak van der Waals inter-actions. Hirshfeld surface analysis indicates that H⋯H (30.2%), N⋯H/H⋯N (22.3%), C⋯H/H⋯C (17.9%) and O⋯H/H⋯O (15.4%) inter-actions make the most significant contributions to the crystal packing.

Asymmetric 2,4-Dienylation/[4 + 2] Annulation Cascade to Construct Fused Frameworks via Auto-Tandem Palladium Catalysis

A palladium catalyzed tandem reaction between ortho-functionalized aryl enones and 2,4-dienyl carbonates has been presented, proceeding through sequential 2,4-dienylation/Michael addition/π-σ-π isomerization/allylic alkylation. A broad array of enantioenriched architectures having fused and spirocyclic frameworks are constructed in moderate to excellent yields and stereoselectivity. Notably, the intrinsic intramolecular Diels-Alder reaction pattern of the dienylated intermediates is well reversed via Pd(0)-π-Lewis base catalysis.

Crystal structure and Hirshfeld surface analysis of N-[2-(5-methyl-furan-2-yl)phen-yl]-3-nitro-N-[(3-nitro-phen-yl)sulfon-yl]benzene-sulfonamide

In the title compound, C₂₃H₁₇N₃O₉S₂, C-H⋯O hydrogen bonds link adjacent mol-ecules in a three-dimensional network, while π-π stacking inter-actions, with centroid-centroid distances of 3.8745 (9) Å, between the furan and an arene ring of one of the two (3-nitro-phen-yl)sulfonyl groups, result in chains parallel to the a axis. The Hirshfeld surface analysis indicates that O⋯H/H⋯O (40.1%), H⋯H (27.5%) and C⋯H/H⋯C (12.4%) inter-actions are the most significant contributors to the crystal packing.

Intramolecular cyclization reactions of arylpropargyl amides of electron-deficient α,β-alkenyl carboxylates and related compounds

Intramolecular cyclization reactions of arylpropargyl amides of electron-deficient α,β-alkenyl carboxylates such as fumarates and ethenetricarboxylates were investigated. The reaction of the fumaramides with a base, Et₃N or DBU in xylenes at 140 °C under air gave benz[f]isoindoline derivatives in 21-63% yields. The benz[f]isoindolines may be produced via the formation of an allenic intermediate, intramolecular Diels-Alder reaction, proton transfer, and dehydrogenation by oxygen. The suitable bases and the product yields depend on the substituents on the benzene ring. On the other hand, the reaction of the amides of fumarate and ethenetricarboxylate by heating in DMSO gave aroyl-substituted pyrrolidine derivatives as major products, probably via addition of water under metal-free conditions. Furthermore, cyclization reactions of H and Me substituted alkyne derivatives were investigated for comparison. The selective formation of various types of products, such as ethyl 2-(1-benzyl-4-formyl-2-oxopyrrolidin-3-yl)acetate and diethyl 2-(1-benzyl-2-oxo-4-vinylidenepyrrolidin-3-yl)malonate, was found, depending upon the alkyne substituents and the reaction conditions. The reaction mechanisms have been discussed using density functional theory (DFT) calculations.

Intramolecular Diels-Alder Reactions of α-Bromostyrene-Functionalized Unsaturated Carboxamides

Intramolecular cycloaddition reactions of α-bromostyrene-functionalized amides of monomethyl fumarate were investigated. The reaction of the amides with Et₃N in toluene at 110 °C gave 1,4-dihydronaphthalenes. The 1,4-dihydronaphthalenes may be produced via the intramolecular Diels-Alder reaction, proton transfer, and dehydrobromination by a base, along with C═C bond isomerization by proton transfer. The reaction of amide derivatives with halogen on a benzene ring and alkali metal carbonates in toluene at 110 °C gave naphthalene derivatives directly. Dehydrogenation of various 1,4-dihydronaphthalenes with cesium or rubidium carbonate in toluene at 110 °C gave naphthalene derivatives. The retardation by TEMPO, acceleration by air for some substrates, and density functional theory calculations suggest a radical mechanism caused by intervention of molecular oxygen.

Hyperbaric reactions in organic synthesis. Progress from 2006 to 2020

This comprehensive review summarizes the published literature data concerning above 1 kbar reactions for the purposes of preparative organic synthesis (more then 50 mg of the initial substance) from 2006...

Crystal structure and Hirshfeld surface analysis of (3aSR,6RS,6aSR,7RS,11bSR,11cRS)-2,2-dibenzyl-2,3,6a,11c-tetra-hydro-1H,6H,7H-3a,6:7,11b-di-epoxy-dibenzo[de,h]isoquinolin-2-ium tri-fluoro-methane-sulfonate

In the cation of the title salt, C30H28NO2 +·CF3O3S-, the four tetra-hydro-furan rings adopt envelope conformations. In the crystal, pairs of cations are linked by dimeric C-H⋯O hydrogen bonds, forming two R 2 2(6) ring motifs parallel to the (001) plane. The cations and anions are connected by further C-H⋯O hydrogen bonds, forming a three-dimensional network structure. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯H (47.6%), C⋯H/H⋯C (20.6%), O⋯H/H⋯O (18.0%) and F⋯H/H⋯F (9.9%) inter-actions.

Crystal structure and Hirshfeld surface analysis of 4,5-di-bromo-2-(4-meth-oxy-phen-yl)-2,3,4,4a,5,6,7,7a-octa-hydro-1H-4,6-ep-oxy-1H-cyclo-penta-[c]pyridin-1-one

The mol-ecule of the title compound, C15H15Br2NO3, comprises a fused tricyclic system consisting of two five-membered rings (cyclo-pentane and tetra-hydro-furan) and one six-membered ring (tetra-hydro-pyridinone). Both five-membered rings of the tricyclic system have envelope conformations, and the conformation of the six-membered cycle is inter-mediate between chair and half-chair. In the crystal, the mol-ecules are linked by C-H⋯O hydrogen bonds and C-H⋯π, C-Br⋯π and C⋯O inter-actions into double layers. The layers are connected into a three-dimensional network by van der Waals inter-actions.

An IMDAF approach to annellated 1,4:5,8-diepoxynaphthalenes and their metathesis reaction leading to novel scaffolds displaying an antiproliferative activity toward cancer cells

A 3,5a-epoxyfuro[2,3,4-de]isoquinoline scaffold, the product of ROCM of 1,4:5,8-diepoxynaphthalenes, is a promising antiproliferative agent toward breast and prostate human cancer cell lines.