A new approach to construction of isoindolo[1,2-a]isoquinoline alkaloids Nuevamine, Jamtine, and Hirsutine via IMDAF reaction

Sustainable tandem acylation/Diels-Alder reaction toward versatile tricyclic epoxyisoindole-7-carboxylic acids in renewable green solvents

Tandem Diels-Alder reactions are often used for the straightforward formation of complex natural compounds and the fused polycyclic systems contained in their precursors. In the second step of this reaction, regio- and stereochemically controlled intramolecular cyclization leads to the formation of versatile nitrogen-containing tricyclic systems. However, these useful organic transformations are usually carried out in highly toxic organic solvents such as benzene, toluene, chloroform, etc. Despite recent efforts by 'green chemists', synthetic chemists still use these traditional toxic organic solvents in many of their reactions, even though safer alternatives are available. However, in addition to the harmful effects of these petrochemical solvents on the environment, the prediction that their resources will run out in the near future has led 'green chemists' to explore solvents that can be derived from renewable resources and used effectively in various organic transformations. In this context, we have shown for the first time that the 100% atom-economical tandem Diels-Alder reaction between aminofuranes and maleic anhydride can be carried out successfully in vegetable oils and waxes. The reaction was successfully carried out in sunflower seed oil, olive oil, oleic acid and lauryl myristate under mild reaction conditions. A series of epoxyisoindole-7-carboxylic acid and bisepoxyisoindole-7-carboxylic acids were obtained in good yields after a practical isolation procedure. The results obtained in this study demonstrate the potential of vegetable oils and their renewable materials to provide a reaction medium that is more sustainable than conventional organic solvents in cascade Diels-Alder reactions and can be used repeatedly without significant degradation. These materials also allow the reaction to be completed in less time, with less energy consumption and higher yields.

Crystal structure and Hirshfeld surface analysis of dimethyl 4-hy-droxy-5,4'-dimethyl-2'-(toluene-4-sulfonyl-amino)-biphenyl-2,3-di-carboxyl-ate

In the title compound, C25H25NO7S, the mol-ecular conformation is stabilized by intra-molecular O-H⋯O and N-H⋯O hydrogen bonds, which form S(6) and S(8) ring motifs, respectively. The mol-ecules are bent at the S atom with a C-SO2-NH-C torsion angle of -70.86 (11)°. In the crystal, mol-ecules are linked by C-H⋯O and N-H⋯O hydrogen bonds, forming mol-ecular layers parallel to the (100) plane. C-H⋯π inter-actions are observed between these layers.

General and Efficient Copper-Catalyzed Oxazaborolidine Complex in Transfer Hydrogenation of Isoquinolines under Mild Conditions

A general and efficient method for copper-catalyzed transfer hydrogenation of isoquinolines with an oxazaborolidine-BH₃ complex, under mild reaction conditions, is successfully developed. A broad range of isoquinolines has been reduced to the corresponding products with 61-85% yields. The method is applied to the synthesis of biologically active tetrahydrosioquinoline alkaloid (±)-norlaudanosine in 62% yield, which is the key precursor for the preparation of (±)-laudanosine, (±)-N-methyl-laudanosine, and (±)-xylopinine in one or two steps.

Crystal strucutre of rac-methyl (11aR*,12S*,13R*,15aS*,15bS*)-11-oxo-11,11a,12,13-tetra-hydro-9H,15bH-13,15a-ep-oxy-isoindolo[1,2-c]pyrrolo[1,2-a][1,4]benzodiazepine-12-carboxyl-ate

The title compound, C₂₁H₁₈N₂O₄, obtained as a racemate, contains a novel heterocyclic system, viz. isoindolo[1,2-c]pyrrolo­[1,2-a][1,4]benzodiazepine. The central diazepane ring has a distorted boat conformation with two phenyl­ene-fused and one methine C atom deviating by 0.931 (1), 0.887 (1) and 0.561 (1) Å, respectively, from the mean plane of the rest of the ring. The γ-lactone ring has an envelope conformation, with the C atom opposite to amide bond deviating by 0.355 (1) Å from its plane. In the crystal, mol­ecules form centrosymmetric dimers through pairs of C—H⋯O hydrogen bonds.

Conversion of oxazolidinediones to isoindoloisoquinolinones via intramolecular Friedel–Crafts reaction

Treatment of oxazolidinediones with TiCl4 in CH2Cl2 resulted in conversion to isoindoloisoquinolinones via intramolecular Friedel–Crafts reaction with extrusion of CO2 in the transformation. The alkaloid nuevamine has been synthesized under these conditions in a regiospecific manner.

Structural optimization of berberine as a synergist to restore antifungal activity of fluconazole against drug-resistant Candida albicans

We have conducted systematic structural modification, deconstruction, and reconstruction of the berberine core with the aim of lowering its cytotoxicity, investigating its pharmacophore, and ultimately, seeking novel synergistic agents to restore the effectiveness of fluconazole against fluconazole-resistant Candida albicans. A structure-activity relationship study of 95 analogues led us to identify the novel scaffold of N-(2-(benzo[d][1,3]dioxol-5-yl)ethyl)-2-(substituted phenyl)acetamides 7 a-l, which exhibited remarkable levels of in vitro synergistic antifungal activity. Compound 7 d (N-(2-(benzo[d][1,3]dioxol-5-yl)ethyl)-2-(2-fluorophenyl)acetamide) significantly decreased the MIC₈₀ values of fluconazole from 128.0 μg mL⁻¹ to 0.5 μg mL⁻¹ against fluconazole-resistant C. albicans and exhibited much lower levels of cytotoxicity than berberine toward human umbilical vein endothelial cells.

rac-Methyl (3aR*,4S*,5R*,7aR*)-5,7a-bis-(acet-yloxy)-3-oxo-2-phenyl-octa-hydro-1H-iso-indole-4-carboxyl-ate

The title molecule, C20H23NO7, the product of nucleophilic cleavage of the 3a,6-ep-oxy bridge in 1-oxo-2-phenyl-octa-hydro-3a,6-ep-oxy-iso-indole-7-carboxyl-ate, comprises a cis-fused bicyclic system containing a 2-pyrrolidinone ring in an envelope conformation (with the C atom bearing the carboxyl-ate substituent as the flap) and a cyclo-hexane ring in a chair conformation. The carboxyl-ate substituent occupies the equatorial position, whereas the two acet-yloxy substituents are in axial positions. The N atom has a trigonal-planar geometry, the sum of the bond angles being 359.3 (3)°. The dihedral angle between the mean plane of the four planar atoms of the pyrrolidinone ring and the phenyl ring is 25.98 (6)°. In the crystal, mol-ecules are linked into zigzag chains along the c-axis direction by C-H⋯O hydrogen bonds.

Methyl (9aR*,10S*,11R*,13aS*,13bS*)-9-oxo-6,7,9,9a,10,11-hexa-hydro-5H,13bH-11,13a-ep-oxy-pyrrolo-[2',1':3,4][1,4]diazepino[2,1-a]isoindole-10-carboxyl-ate

The title compound, C(17)H(18)N(2)O(4), is the methyl ester of the adduct of intra-molecular Diels-Alder reaction between maleic anhydride and 1-(2-fur-yl)-2,3,4,5-tetra-hydro-1H-pyrrolo-[1,2-a][1,4]diazepine. The mol-ecule comprises a fused penta-cyclic system containing four five-membered rings (viz. pyrrole, 2-pyrrolidinone, tetra-hydro-furan and dihydro-furan) and one seven-membered ring (1,4-diazepane). The pyrrole ring is approximately planar (r.m.s. deviation = 0.003 Å) while the 2-pyrrolidinone, tetra-hydro-furan and dihydro-furan five-membered rings have the usual envelope conformations. The central seven-membered diazepane ring adopts a boat conformation. In the crystal, mol-ecules are bound by weak inter-molecular C-H⋯O hydrogen-bonding inter-actions into zigzag chains propagating in [010]. In the crystal packing, the chains are stacked along the a axis.

(6aS*,6bS*,11R*,11aR*)-6-(2-Furyl-methyl)-5,12-dioxo-5,6,6a,6b,7,11,11a,12-octa-hydro-furo[3',2':5,6]isoindolo[2,1-a]quinazoline-11-carb-oxy-lic acid

The title compound, C₂₃H₁₈N₂O₆, is the product of an intra­molecular thermal cyclo­addition within 1-malein-2-[(E)-2-(2-fur­yl)vin­yl]-4-oxo-3,4-dihydro­quinazoline. The mol­ecule comprises a previously unknown fused penta­cyclic system containing two five-membered rings (2-pyrrolidinone and furan) and three six-membered rings (benzene, 2,3-dihydro-4-pyrimidinone and dihydro­cyclo­hexa­ne). The central five-membered pyrrolidinone ring has the usual envelope conformation. The six-membered dihydro­pyrimidinone and dihydro­cyclo­hexane rings adopt a half-boat and a half-chair conformation, respectively. The dihedral angle between the planes of the terminal benzene and furan rings is 45.99 (7)°. In the crystal, O—H⋯O hydrogen bonds link the mol­ecules into centrosymmetric dimers. Weak C—H⋯O hydrogen bonds consolidate further the crystal packing, which exhibits π–π inter­actions, with a short distance of 3.556 (3) Å between the centroids of benzene rings of neighbouring mol­ecules.

Molecular complexity via C-H activation: a dehydrogenative Diels-Alder reaction

Traditionally, C-H oxidation reactions install oxidized functionality onto a preformed molecular skeleton, resulting in a local molecular change. The use of C-H activation chemistry to construct complex molecular scaffolds is a new area with tremendous potential in synthesis. We report a Pd(II)/bis-sulfoxide-catalyzed dehydrogenative Diels-Alder reaction that converts simple terminal olefins into complex cycloadducts in a single operation.

Dearomatization strategies in the synthesis of complex natural products

Evolution in the field of the total synthesis of natural products has led to exciting developments over the last decade. Numerous chemoselective and enantioselective methodologies have emerged from total syntheses, resulting in efficient access to many important natural product targets. This Review highlights recent developments concerning dearomatization, a powerful strategy for the total synthesis of architecturally complex natural products wherein planar, aromatic scaffolds are converted to three-dimensional molecular architectures.

8a-Methyl-5,6,8,8a,9,10-hexa-hydro-10,12a-epoxy-isoindolo[1,2-a]isoquinolinium iodide

The title compound, C(17)H(18)NO(+)·I(-), is an adduct resulting from an intra-molecular Diels-Alder reaction of methallyl chloride with 3,4-dihydro-1-furylisoquinoline. The cation comprises a fused penta-cyclic system containing three five-membered rings (dihydro-pyrrole, dihydro-furan and tetra-hydro-furan) and two six-membered rings (tetra-hydro-pyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered tetra-hydro-pyridine ring adopts the unsymmetrical half-boat conformation. In the crystal, cations and iodide anions are bound by weak inter-molecular hydrogen-bonding inter-actions into a three-dimensional framework.

Methyl 7,8-diacet-oxy-11-oxo-5-(2-oxo-pyrrolidin-1-yl)-7,9-epoxy-cyclo-penta-[4,5]pyrido[1,2-a]quinoline-10-carboxyl-ate sesquihydrate

The title compound, C(26)H(28)N(2)O(9)·1.5H(2)O, the product of an acid-catalysed Wagner-Meerwein skeletal rearrangement, crystallizes as a sesquihydrate with the O atom of one of the two independent water mol-ecules occupying a special position on a twofold axis. The organic mol-ecule comprises a fused penta-cyclic system containing two five-membered rings (cyclo-pentane and tetra-hydro-furan) and three six-membered rings (piperidinone, tetra-hydro-pyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered piperidinone and tetra-hydro-pyridine rings adopt boat and sofa conformations, respectively. In the crystal, there are three independent O-H⋯O hydrogen bonds, which link the organic mol-ecules and water mol-ecules into complex two-tier layers parallel to (001). The layers are further linked into a three-dimensional framework by attractive inter-molecular carbon-yl-carbonyl inter-actions.