One-Step Synthesis of the Benzocyclo[penta- to octa-]isoindole Core

Regioselective Synthesis of the Tetrahydrocarbazole Core of Akuammiline Alkaloids via Palladium-Catalyzed Intramolecular Arylation Reaction

Tetrahydrocarbazole is the central core for several biologically active alkaloids, and regioselective synthesis of this core is a challenging task. Herein, we report an efficient strategy for the synthesis of this core involving palladium-catalyzed intramolecular arylation reaction with excellent regioselectivity (>99%) starting from N-phenyl-bromoalkene without having any relocation of double bonds via competitive palladium-catalyzed isomerization reaction. Broad functional group tolerance and exclusive regioselectivity have been observed for meta-substituted halide substrates. Furthermore, this reaction can be scalable on the gram scale.

Experimental and Computational Studies of Palladium-Catalyzed Spirocyclization via a Narasaka-Heck/C(sp3 or sp2)-H Activation Cascade Reaction

The first synthesis of highly strained spirocyclobutane-pyrrolines via a palladium-catalyzed tandem Narasaka-Heck/C(sp³ or sp²)-H activation reaction is reported here. The key step in this transformation is the activation of a δ-C-H bond via an in situ generated σ-alkyl-Pd(II) species to form a five-membered spiro-palladacycle intermediate. The concerted metalation-deprotonation (CMD) process, rate-determining step, and energy barrier of the entire reaction were explored by density functional theory (DFT) calculations. Moreover, a series of control experiments was conducted to probe the rate-determining step and reversibility of the C(sp³)-H activation step.

trans-Carbocarbonation of Internal Alkynes through a Formal anti-Carbopalladation/C-H Activation Cascade

An intramolecular Pd-catalyzed cascade reaction is presented that consists of a formal anti-carbopalladation of a C-C triple bond followed by C-H activation. As a result, oligocyclic ring systems with an embedded tetrasubstituted double bond are formed. The key to success in affording the trans geometry of the emerging double bond are alkyne units with residues that must not undergo β-hydride elimination (e.g., t-butyl or silyl groups). Silyl groups proved to be a perfect handle to further convert the tetrasubstituted alkenes. The evaluation of kinetic data with a deuterium-labeled compound and X-ray analyses of trapped intermediates provided additional insight into the catalytic cycle.

Direct Access to Fused Salicylaldehydes and Salicylketones from Tetraynes

A facile method for the synthesis of fused, multifunctionalized salicylaldehydes and salicylketones by a one-pot, three-step cascade hexadehydro-Diels-Alder (HDDA) reaction of tetraynes followed by an intermolecular aldehyde/ketone reaction and hydroxylation is reported. Target compounds were prepared by the condensation of malonates with 3-bromo-1-propyne, and the resulting 2,2-di(1-propyn-3-yl)malonates underwent cross-coupling with phenylethynyl bromides to afford 2,2-di(5-phenyl-2,4-pentadiynyl)malonates, which underwent intramolecular cyclization to produce bicyclic salicylaldehydes. The overall transformation involves the formation of four new C-C bonds and one new C_aryl -O bond through both intramolecular and intermolecular reactions. The reaction is easy to perform, proceeds under mild conditions, and exhibits excellent regioselectivity. Water, a simple and readily available reagent, was employed as the OH source. A plausible reaction mechanism is proposed for this new annulation based on isotopic substitution experiments.

Fused multifunctionalized isoindole-1,3-diones via the coupled oxidation of imidazoles and tetraynes

The facile synthesis of fused multifunctionalized isoindole-1,3-diones by a hexadehydro-Diels–Alder domino reaction of various substituted tetraynes and imidazole derivatives is reported.

Pd-catalyzed intramolecular C-N bond cleavage, 1,4-migration, sp3 C-H activation, and Heck reaction: four controllable diverse pathways depending on the judicious choice of the base and ligand

Diverse and controllable pathways induced by palladium-catalyzed intramolecular Heck reaction of N-vinylacetamides for the synthesis of nitrogen-containing products in reasonable to high yields via tuning the phosphine ligands and bases are reported. Domino reactions including unique β-N-Pd elimination, 1,4-Pd migration, or direct acyl C-H bond functionalization were found to be involved forming different products, respectively. Given the ability of using the same starting material to generate diverse products via completely different chemoselective processes, these current methodologies offer straightforward access to valuable nitrogen-containing products under mild reaction conditions as well as inspire the discovery of novel reactions.

One-step synthesis of diazaspiro[4.5]decane scaffolds with exocyclic double bonds

Unactivated yne-en-ynes reacted with a range of substituted aryl halides in the presence of Pd(OAc)2-PPh3 to afford diazaspiro[4.5]decane with exocyclic double bonds. Three carbon-carbon bonds are formed in this domino reaction, which involves highly regioselective C-C coupling and spiro scaffold steps.

Convenient one-step construction of yne-functionalized aryl halides through domino cyclization from tetraynes

An efficient method for the construction of fused yne-substituted aryl halides by reaction of unactivated linear tetraynes with allyl halides via domino C-C coupling and formation of C-X bonds in the presence of Pd(OAc)2/PPh3 was developed.

2-Tosyl-2,3,3a,4,9,9a-hexa-hydro-1H-benzo[f]isoindol-1-one

The title compound, C19H19NO3S, was produced by the self-reaction of N-cinnamyl-N-tosyl-acryl-amide in the presence of palladium(II) acetate via an intra-molecular C-C coupling reaction and C-H activation. There are two chiral C atoms in the mol-ecule, but the crystal is a racemic system due to a lack of chiral separation. The five-membered ring is twisted about the methyl-ene-methane bond, and the cyclo-hexa-1,4-diene ring has a boat conformation. The dihedral angle between the benzene rings is 88.27 (14)°, indicating an almost orthogonal relationship and an approximate L-shape for the mol-ecule. In the crystal, the presence of C-H⋯π inter-actions leads to inversion dimers.

2-(4-Methyl-phen-yl)-3-oxo-4-phenyl-2,3,3a,4,9,9a-hexa-hydro-1H-benzo[f]iso-indole-6-carbo-nitrile

In the title compound, C₂₆H₂₂N₂O, one phenyl ring, one five-membered N-heterocyclic ring and one six-membered carbocyclic ring make up the hexa­hydro­benzo[f]iso­indole core. Another phenyl group is attached to the heterocyclic N atom as a substituent. The non-aromatic five- and six-membered rings both exhibit boat conformations. In the crystal, weak C—H⋯O and C—H⋯N inter­actions establish the observed three-dimensional structure. The crystal studied was refined as an inversion twin.

4-(4-Fluoro-benzo-yl)-3-phenyl-3,4-di-hydro-naphthalen-1(2H)-one

In the title compound, C₂₃H₁₇FO₂, the cyclo­hexenone ring has an envelope conformation, the flap atom being the C atom to which the phenyl ring is attached. The 4-fluoro­benzoyl ring and the phenyl ring are inclined to one another by 28.77 (7)°, and by 52.00 (7) and 44.77 (7) °, respectively, to the aromatic ring fused to the cyclo­hexenone ring. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming a two-dimensional network lying parallel to (100).

(E)-4-[(1-Benzyl-4-benzyl-idene-2,5-di-oxopyrrolidin-3-yl)meth-yl]benzalde-hyde 0.25-hydrate

The crystal structure of the title compound, C₂₆H₂₁NO₃·0.25H₂O, reveals one stereogenic centre in the mol­ecule. Nevertheless, due to the observed centrosymmetric space group, both enanti­omers are present in the crystal packing. The water molecule of crystallisation is located on a crystallographic inversion center. The mol­ecule contains one five-membered ring (A) and three six-membered rings (benzyl ring B, benzyl­idene ring C and formyl­benzyl ring D). All four rings are not coplanar: the dihedral angles between rings A and B, A and C, and A and D are 70.35 (9), 33.8 (1) and 60.30 (9)°, respectively. In the crystal, pairs of weak C—H⋯O inter­actions lead to the formation of centrosymmetric dimers. Additional C—H⋯O inter­actions link the dimers into chains along [011].

Ethyl 4-acetyl-5-oxo-3-phenyl-hexa-noate

The reaction of ethyl 3-bromo-3-phenyl­propano­ate with pentane-2,4-dione, in the presence of palladium(II) acetate and triphenyl­phosphine, in dimethyl­formamide, unexpectedly gave the title product, C₁₆H₂₀O₄. The mol­ecule contains one chiral C atom but the crystal is racemic. In the crystal, neighboring mol­ecules form a chain along [100] through three weak C—H⋯O inter­actions. Furthermore, a double-stranded structure is formed through weak C—H⋯O inter­actions between two parallel chains.