Sequential Cross‐Coupling/Annulation of ortho‐Vinyl Bromobenzenes with Aromatic Bromides for the Synthesis of Polycyclic Aromatic Compounds

Abstract

A sequential cross‐coupling/annulation of ortho‐vinyl bromobenzenes with aromatic bromides was realized, providing a direct and modular approach to access polycyclic aromatic compounds. A vinyl‐coordinated palladacycle was proposed as the key intermediate for this sequential process. Excellent chemoselectivity and regioselectivity were observed in this transformation. The practicability of this method is highlighted by its broad substrate scope, excellent functional group tolerance, and rich transformations associated with the obtained products.

Regioselective Tandem C–H Alkylation/Coupling Reaction of ortho-Iodophenylethylenes via C,C-Pallada(II)cycles

“…1a In recent years, our group has developed aryl-alkenyl-palladacycle-based transformations for the synthesis of multisubstituted arylethylenes 11 and polycyclic aromatic compounds. 12 The substrate scope of these reactions is limited to α-substituted ortho-halo phenylethylenes, in which the αsubstituents were supposed to promote cyclopalladation through steric congestion (Figure 1B). 13 To the best of our knowledge, substrates without α-substitution have not been applied in this kind of reactions yet.…”

“…Zhang and co-workers developed a three-component alkylation/Heck reaction of 2-iodobiphenyls with a preliminary investigation of the very poor reaction regioselectivity of unsymmetrically substituted biaryl iodides. 16 In our previous study of the tandem cross-coupling/ annulation of ortho-bromophenylethylenes with aryl bromides, 12 aryl bromides were found to be selectively coupled to the alkenyl position of α-substituted ortho-bromophenylethylenes, while the origin of this selectivity remains unknown.…”

“…For example (Figure A), in the arylbicycloheptylpalladium complexes, the rigid norbornyl skeleton placing the arene ortho C–H bond right beside the palladium­(II) center enables convenient cyclopalladation to generate the aryl-norbornyl-palladacycle species, which is the key intermediate in Catellani-type reactions. , Facile cyclopalladation of the neopentyl type alkylpalladium species could be achieved as a result of the Thorpe–Ingold effect of the quaternary carbon, thus providing an efficient access to diverse complex spiro-fused polycyclic and chiral heterocyclic compounds bearing all-carbon quaternary stereocenters . In recent years, our group has developed aryl-alkenyl-palladacycle-based transformations for the synthesis of multisubstituted arylethylenes and polycyclic aromatic compounds . The substrate scope of these reactions is limited to α-substituted ortho -halo phenylethylenes, in which the α-substituents were supposed to promote cyclopalladation through steric congestion (Figure B) .…”

“…Zhang and co-workers developed a three-component alkylation/Heck reaction of 2-iodobiphenyls with a preliminary investigation of the very poor reaction regioselectivity of unsymmetrically substituted biaryl iodides . In our previous study of the tandem cross-coupling/annulation of ortho -bromophenylethylenes with aryl bromides, aryl bromides were found to be selectively coupled to the alkenyl position of α-substituted ortho -bromophenylethylenes, while the origin of this selectivity remains unknown. Although recently a number of tandem reactions have been developed potentially involving aryl-aryl-palladacycles or aryl-alkenyl-palladacycles, , these transformations are confined to domino annulation or disilylation reactions in which the regioselectivity issue was originally evaded.…”

Sequential Cross‐Coupling/Annulation of ortho‐Vinyl Bromobenzenes with Aromatic Bromides for the Synthesis of Polycyclic Aromatic Compounds

“…Zuschriften (3ap), quinoline (3aq, 3au, 3ay), benzo[d]thiazole (3ar), quinoxaline (3at), pyridine (3as, 3ax), thiophene (3aw)a nd benzofuran (3av), were well tolerated in this sequential process.E xcellent regioselectivities were also observed for 3at-3 ay, [13] which is ascribed to the prominent difference between two C À Hb onds for palladium promoted activation in these heteroaromatic system. [14] To illustrate the synthetic scope of this method, several experiments were carried out.…”