C–H activation route to dibenzo[a,e]pentalenes: annulation of arylacetylenes promoted by PdCl2–AgOTf–o-chloranil

Abstract

A novel catalytic C-H activation route to privileged dibenzo[a,e]pentalene (DBP) structures has been established. In the presence of PdCl 2 , AgOTf, and o-chloranil, a C-H/C-H annulation of arylacetylenes takes place to furnish the corresponding DBPs. A number of mechanistic experiments indicate that this new annulation occurs through alkyne-directed, ortho-selective, electrophilic aromatic C-H palladation. Not only symmetric diarylacetylenes but also unsymmetric arylacetylenes are applicable to this reaction. UV-vis absorption spectra and DFT studies on the resulting DBPs indicate a strong substituent effect on the energy levels of the HOMO and HOMOÀ1 of DBPs.

Collaborative Interaction of Carbon–Carbon Unsaturated Bond Groups with Transition-metal Catalysts for C–H Bond Functionalization

“…Diarylethynes undergo ortho-CH bond cleaving annulation to give dibenzo[a,e]pentalenes in the presence of PdCl 2 catalyst, o-chloranil as an oxidant, and AgOTf (Scheme 23). 30 Ethyl phenylpropiolate also undergoes the similar annulation reaction regioselectively to give diethyl dibenzo[a,e]pentalene-5,10-dicarboxylate. The observed substrate reactivity and mechanistic studies support a scenario of alkyne-directed, ortho-selective, electrophilic CH palladation, which triggers the transformation.…”

Pd-catalyzed cascade cyclization of o -alkynylarylbromides with dialkylalkynes via consecutive carbopalladation

“…1f,i Various types of Pd-catalyzed intra-and intermolecular cascade reactions of enynes and dienes including consecutive carbopalladation followed by termination with b-hydride elimination, cross-coupling, C-H bond functionalization, and nucleophilic addition have been achieved. [3][4][5][6][7][8][9][10][11] For example, Grigg et al reported an intra-and intermolecular four consecutive carbopalladation of ene triyne and yne triene with allene. 4 Recently, we have developed a new Pd-catalyzed crossover-annulation of o-alkynylarylhalides and diarylalkynes for the synthesis of the multisubstituted dibenzo[a,e]pentalenes (Scheme 1a).…”

Dehydrogenative Heck Annelations of Internal Alkynes

“…Heck-type addition of the latter leads to 17C, which evolves to the product by elimination of HPdX. Recently, the Itami and Segawa research team disclosed the palladium(II) chloride catalyzed synthesis of dibenzo[a,e]pentalenes from diarylacetylenes (Equation 46) or ethyl 3-phenylpropiolate (Equation 47) in the presence of stoichiometric amounts of both silver triflate and ochloranil 59. That these two additives are required in order to effectively perform these DHRs could explain why such coupling has not previously been reported.…”