Efficient Activation of Aromatic CH Bonds for Fused Polyaromatic Hydrocarbon Construction

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.

Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems

The release of the inherent ring strain of cyclobutane and cyclopropane derivatives allows a rapid build-up of molecular complexity. This review highlights the state-of-the-art of the ring expansions of three- and four-membered cycles and is organised by types of reactions with emphasis on the reaction mechanisms. Selected examples are discussed to illustrate the synthetic potential of this elegant synthetic tool.

Rapid construction of cyclopenta[b]naphthalene frameworks from propargylic alcohol tethered methylenecyclopropanes

We have developed a new synthetic methodology for the rapid construction of cyclopenta[b]naphthalene frameworks from the reaction of propargylic alcohol tethered methylenecyclopropanes with mesyl chloride in the presence of triethylamine through cascade cyclization. The reaction can be performed under mild conditions without the use of transition metals, affording the target products in moderate to good yields, and this cyclization reaction process can be scaled up to a gram-scale synthesis.

Lewis or Brønsted acid-catalysed reaction of propargylic alcohol-tethered alkylidenecyclopropanes with indoles and pyrroles for the preparation of polycyclic compounds tethered with indole or pyrrole motif

We developed a facile synthetic method to access the cyclopenta[b]naphthalene skeleton from Lewis or Brønsted acid-catalysed propargylic alcohol-tethered alkylidenecyclopropanes with indole and pyrrole derivatives.

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.

Palladium(0)-Catalyzed Intermolecular Carbocyclization of (1,n)-Diynes and Bromophenols: An Efficient Route to Tricyclic Scaffolds

A novel palladium(0)-catalyzed dearomative cyclization reaction of bromophenols with (1,n)-diynes has been developed for building two new types of tricyclic architectures containing a quaternary carbon center. This method employs inexpensive bromophenols, and easily accessible tethered diynes. It exhibits a broad substrate scope and tolerates various functional groups. Preliminary results with commercially available chiral ligands indicate that enantioselective variants are feasible for both cyclization processes.

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.