Fused Phenanthridines: Domino Cyclization of 1,6-Diynes with Bromo(iso)quinoline

Nickel-Catalyzed Tandem Cyclization of 1,6-Diynes with Indolines/Indoles through Dual C-H Bond Activation

A nickel-catalyzed site-selective tandem cyclization of 1,6-diynes with substituted indolines or indoles through consecutive dual C-H bond activation is described. In the reaction, substituted fused indole and carbazole derivatives were observed in good to excellent yields, in which three consecutive C-C bonds formed in one pot. Later, in the presence of DDQ, the aromatization of the indoline derivative was converted to the indole derivative. A possible reaction mechanism involving dual C-H bond activation as a key step was proposed to account for the present reaction.

Combined Experimental and Computational Study on Ruthenium(II)-Catalyzed Reactions of Diynes with Aldehydes and N,N-Dimethylformamide

Cycloaddition reactions of 1,6-diynes bearing methyl terminal groups with p-anisaldehyde were conducted using a cationic ruthenium catalyst with a η⁵-pentamethylcyclopentadienyl ligand in THF at room temperature to afford dienyl ketones via ring opening of the initially formed fused pyrans. (Z)-Stereoisomers of dienyl ketones were selectively obtained using the ruthenium catalyst, whereas previously reported rhodium catalysts produced (E)-isomers. These (E)- and (Z)-selectivities are kinetically controlled as the control experiments showed that the E/Z-isomerization of (E)-dienylketone occurs at 70 °C for 10 h to afford an E/Z-ratio of almost 1:1. The origin of this characteristic stereoselectivity for the ruthenium catalyst was attributed to the direct ring opening of the CpRu⁺-coordinated pyran complex intermediates on the basis of theoretical calculations [PCM (THF) M06L/SDD-6-311++G(d,p)//B3LYP/LanL2DZ-6-31G(d)] and control experiments. The (Z)-selectivity increased when the bulkiness of the diyne terminal substituents increased. Notably, the reaction of 1,6-diynes bearing tert-butyl terminal groups with various α,β-unsaturated aldehydes exclusively afforded (Z)-dienyl ketones even at 70 °C when a cationic ruthenium complex with a smaller η⁵-cyclopentadienyl (Cp) ligand was used as the catalyst. The same Cp complex was found to be also efficient for the hydrocarbamoylative cyclization of sterically demanding 1,6-diynes bearing tertiary or quaternary carbon tethers with N,N-dimethylformamide.

Palladium(II)-catalyzed sequential C-H arylation/aerobic oxidative C-H amination: one-pot synthesis of benzimidazole-fused phenanthridines from 2-arylbenzimidazoles and aryl halides

Starting from 2-arylbenzimidazoles and aryl halides, an efficient palladium-based catalytic method for the synthesis of benzimidazole-fused phenanthridines has been developed. This reaction sequence comprises intermolecular C-H arylation and intramolecular aerobic oxidative C-H amination, involving the rupture of two C-H bonds, one C-X bond, and one N-H bond in one pot. The Pd(II)-Pd(IV)-Pd(II) and Pd(II)-Pd(0)-Pd(II) catalytic cycles work together under the reported conditions to generate phenanthridines with diverse substituents.

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.

Iron-catalyzed formation of 2-aminopyridines from diynes and cyanamides

Diynes and cyanamides undergo an iron-catalyzed [2 + 2 + 2] cycloaddition to form highly substituted 2-aminopyridines in an atom-efficient manner that is both high yielding and regioselective. This system was also used to cyclize two terminal alkynes and a cyanamide to afford a 2,4,6-trisubstituted pyridine product regioselectively.

(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].